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  • Articles  (1,611)
  • Blackwell Publishing Ltd
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (1,611)
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  • Articles  (1,611)
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  • 1
    Electronic Resource
    Electronic Resource
    Manufacturing SiC-Fiber-Reinforced SiC Matrix Composites by Improved CVI/Slurry Infiltration/Polymer Impregnation and Pyrolysis (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two- and three-dimensional SiCr/SiC composites have been prepared starting from Tyranno SA(tm) fiber preforms. Preform densification has been performed by a modified preceramic polymer impregnation and pyrolysis (PIP) process consisting of filling the preform large interbundle voids with SiC powder before the PIP process. This step was accomplished by low-pressure infiltration of a SiC powder dilute slurry through the preform thickness. Specimens were further processed with polymer impregnation and pyrolysis to determine the effects on structural, thermal, and mechanical properties of the obtained composites. High-temperature pyrolysis treatment, which promoted polymer derived SiC matrix crystallization, markedly increased thermal diffusivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20093.x
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  • 2
    Electronic Resource
    Electronic Resource
    Fourier-Transform Infrared Spectrometry Measurement of Emissions Concentration from Glass Manufacturing (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Carbon is commonly added to sulfate-fined silicate-glass batches to enhance the fining process. Reactions between carbon and Na2SO4 modify the SOx emissions from Na2SO4 decomposition. Fourier-transform infrared (FTIR) spectrometry is used to analyze the emission of air pollutants from the isothermal decomposition of Na2SO4 + C undertaken using thermogravimetric analysis (TGA). The FTIR spectrometer is calibrated using standard gas mixtures containing CO, CO2, SO2, NO, and NO2. The collected spectra are quantified using the classical least-squares (CLS) approximation. The TGA-FTIR system provides SOx, and COx, concentrations versus time data from the isothermal decomposition of Na2SO4, in the presence of a carbon black. Mass spectrometry (MS) complements FTIR by being able to detect SO(g).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20094.x
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  • 3
    Electronic Resource
    Electronic Resource
    Low-Temperature Sintering and Piezoelectric Properties of 0.6Pb(Zr0.47Ti0.53)O3·0.4Pb(Zn1/3Nb2/3)O3 Ceramics (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The sintering behavior and piezoelectric properties of the lead zirconate titanate (Pb(ZrTi)O3, PZT)–lead zinc niobate (Pb(Zn1/3Nb2/3)O3, PZN) system were investigated. The sintering temperature required for full densification of the PZT-PZN system was significantly lowered when the proportion of PZN was increased. The density of the specimen composed of 60% PZT and 40% PZN (0.6PZT-0.4PZN, Pb((Zr0.47Ti0.53)0.6–(Zn1/3Nb2/3)0.4)O3) sintered at 880°C for 4 h was 8.15 g/cm3, which was 〉97% of the theoretical value. This improved densification behavior was attributed to the combined effects of the high sinterability of PZN and the stability of the PZT pcrovskite structure. The piezoelectric and dielectric properties of the 0.6PZT-0.4PZN specimen sintered at 880°C were comparable with those of a specimen with the same composition sintered at 1200°C for 2 h. The piezoelectric coefficient (d33) and the electromechanical coupling factor (kp) of the 0.6PZT-0.4PZN specimen sintered at 880°C were 460 pC/N and 0.6, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20095.x
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  • 4
    Electronic Resource
    Electronic Resource
    Dielectric Properties of 0.8Pb[(Mg1/3Ta2/3),(B‘1/3B“2/3)]O3–0.2PbTiO3 Ceramics (B'B”= ZnTa, MgNb, and ZnNb) (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Octahedral cations of Mg and Ta in Pb[(Mg1/3Ta2/3)0.8Ti0.2]O3 were replaced independently as well as simultaneously by Zn and Nb, respectively, to investigate the effects of composition modification on phase formation and dielectric properties. When Mg was replaced by Zn, the perovskite formation yields decreased continuously to 0% with the Zn fraction. In contrast, nearly phase-pure perovskite powders could be prepared when Ta and the Mg-Ta complex were replaced by Nb and Zn-Nb, respectively. Dielectric relaxation with diffuse phase transition was observed at most of the compositions. Dielectric maximum temperatures increased steadily with the substituent fractions, whereas variations of the maximum dielectric constant were dependent heavily on the substituent species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20096.x
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  • 5
    Electronic Resource
    Electronic Resource
    Reexamination of the Role of SrMoO4 in the Enhancement of the Low-Field Magnetoresistance of Sr2FeMoO6 (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Different ratios of the precursor phases of SrFeO3–x (SFO) and SrMoO4 (SMO) were used to prepare Sr2FeMoO6 (SFMO) by a solid-state reaction. X-ray diffraction was used to identify the phases. A residual SMO was observed to exist in the sample with an SFO/SMO ratio of 0.9:1. The sample with a residual SMO phase had higher resistivity, lower magnetization, but higher low-field magnetoresistance (LFMR). High-resolution transmission electron microscopy was used to identify the compositions and phases. Nanometer-sized amorphous-like clusters of SMO phase were located inside the grains rather than at grain boundaries; however, some boundaries were rich in the strontium ion. The possible mechanisms for the conduction and the increase of LFMR of SFMO are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20098.x
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and Characterization of Hexapod-Shaped Tetragonal-Phase Barium Titanate Single Crystals (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hexapod-shaped tetragonal-phase BaTiO3 single crystals have been synthesized using a simple hydrothermal method. The effects of alkali concentration, precursors, and temperature on the morphology are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20099.x
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  • 7
    Electronic Resource
    Electronic Resource
    Fracture Toughness Measurement of Chromium Nitride Films on Brass (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two methods of measuring the fracture toughness of films are critically examined using well-characterized films of CrN and Cr2N ˜6 μm in thickness bonded to brass. The first method invokes a model developed by Beuth and Klingbeil in which the film fracture stress is related to the fracture energy through an expression that accounts for work hardening of the substrate. The second method is to directly measure the displacement field around the crack tip using electron-beam molrè and, subsequently, to estimate the crack-tip stress Intensity factor using full-field-displacement equations. The films are prepared by magnetron sputtering on brass substrates heat-treated at various temperatures, thereby altering the microstructure and, hence, the substrate yield stress. Unexpectedly, the same films deposited on various substrates lead to very different in-plane compressive residual stresses. The effect on crack-driving force is discussed, and a comparison between these two methods is made. Both techniques agree reasonably well and reveal that CrN exhibits a higher toughness than Cr2N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.tb20097.x
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  • 8
    Electronic Resource
    Electronic Resource
    Dielectric Properties of Ba(SnxTi1−x)O3 Thin Films Grown by a Sol–Gel Process (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ferroelectric Ba(SnxTi1−x)O3 (BTS) thin films were deposited using a sol–gel process on LaNiO3-coated silicon substrates. The films showed a (100) preferred orientation depending on composition. The grain size decreased and the microstructure became denser with increasing tin content. The decreasing grain size with increasing tin may be attributable to lower grain-growth rates from the more slowly diffusing Sn4+ ion, which has a larger ionic radius than Ti4+. The ferroelectric phase transition temperature of Ba(SnxTi1−x)O3 thin films with (a) x= 0, (b) x= 0.05, (c) x= 0.10, and (d) x= 0.15 occurs at about 150°, 45°, 28°, and 20°C, respectively. The highest K (figure of merit defined as K= tunability/tan δ={[ɛ(0) −ɛ(E)]/ɛ(E)}/tan δ) was found for BTS thin films with x= 0.10, even though tunability was highest with x= 0.05. An increase of dielectric loss as compared with films with x= 0.10 produced a decrease in K value. The J–E characteristics were highly nonlinear and the electric field resulting in nonlinearity moved to lower electric fields with decreasing tin content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07495.x
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  • 9
    Electronic Resource
    Electronic Resource
    Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Er3+-doped sodium lanthanum aluminosilicate glasses with compositions of (90−x)(0.7SiO2·0.3Al2O3)·xNa2O·8.2La2O3· 0.6Er2O3·0.2Yb2O3·1Sb2O3 (in mol%) (x= 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ωt (t= 2, 4, 6) decreases with increasing Na2O. Ω2 decreases rapidly with increasing Na2O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2O. Fluorescence spectra of the 4I13/2 to 4I15/2 transition have been measured and the change with Na2O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2O.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07496.x
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  • 10
    Electronic Resource
    Electronic Resource
    Elastic Properties of Nickel-Based Anodes for Solid Oxide Fuel Cells as a Function of the Fraction of Reduced NiO (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The changes in porosity and elastic moduli of YSZ-containing nickel-based anode materials for solid oxide fuel cells were studied as a function of the fraction of reduced NiO. Anode samples were reduced in a gas mixture of 4% hydrogen and 96% argon for different periods of time at 800°C and their Young's and shear moduli were determined afterward at room temperature using resonant ultrasound spectroscopy and impulse excitation. It was found that the magnitude of Young's and shear moduli decreased significantly with increasing fraction of reduced NiO and that the magnitude of the elastic moduli of a fully reduced Ni–YSZ anode was ∼45% lower than that of unreduced NiO–YSZ. Because the elastic moduli of NiO are close to those of Ni, the observed decrease in the magnitude of the elastic moduli was found to be caused mainly by the significant increase in the porosity of the sample as a result of NiO reduction. Expressions are presented for the amount of porosity and the magnitude of the elastic moduli as a function of the fraction of reduced NiO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07499.x
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  • 11
    Electronic Resource
    Electronic Resource
    Investigation of Lamella-Twinned Crystallites and Dislocations in Paraelectric Phases of Bi2O3-Doped BaTiO3 (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Defects in the paraelectric phases of BaTiO3 doped with Bi2O3 were analyzed by transmission electron microscopy under two-beam conditions. (111) twin structures were characterized by selected area diffraction and bright-field images. The orientation relationships of the (111) twins were determined using stereograms. Lamella-twinned crystallites included in the paraelectric phases were found in this system. Pure wedge fringes were analyzed in these grains using electron diffraction and imaging techniques. Double diffraction was observed in the overlapped regions of the matrix and the microtwin in the [113] direction, and high-density dislocation loops were seen in some grains. Weak-beam dark-field microscopy techniques were used to observe the dislocation loops, which predominately lay on {100} crystal planes with Burgers vectors a〈100〉, and were found to be pure edge dislocations. Some dislocations were transformed into crystallographic shear planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07500.x
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  • 12
    Electronic Resource
    Electronic Resource
    Experimental Determination and Thermodynamic Calculation of the Zirconia–Calcia–Magnesia System at 1600°, 1700°, and 1750°C (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Phase relations in the ternary system ZrO2–CaO–MgO were experimentally established at 1600°, 1700°, and 1750°C. The investigation was based on powder X-ray diffractometry, scanning electron microscopy–energy dispersive spectroscopy, and electron probe microanalysis, on 24 ternary compositions. The compositions were prepared using attrition milling of respective oxides and carbonates as raw materials. The results obtained allowed construction of the corresponding isothermal sections, which verified the existence of the cubic-ZrO2–CaZrO3 phase compatibility field at the three temperatures. Finally, experimental results also were compared with the thermodynamic assessment previously reported of the system ZrO2–CaO–MgO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07503.x
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  • 13
    Electronic Resource
    Electronic Resource
    Improved Hydration Resistance of Synthesized Magnesia–Calcia Clinker by Surface Modification (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydration resistance of synthesized MgO–CaO clinker was improved by surface modification using oleic acid, stearic acid, or complex acids as modifiers, with phosphoric acid as a reference. Unmodified and modified samples were evaluated using a powdering resistance test, weight change test, and flowability test. The remarkable effects of the modifiers on the hydration resistance and flowability of the clinker were manifested, and the complex modifier caused the most significant effect. The mechanism involved the formation of calcium-containing films on the surfaces of the clinker particles, which protected them from hydration. The flowability of the clinker also increased with improved hydration resistance because of the decreased bonded-moisture content. Comparison of infrared spectra between unmodified and modified samples confirmed the formation of surface films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07485.x
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  • 14
    Electronic Resource
    Electronic Resource
    In Situ Synthesis of TiN Particulate/Titanium Silicide Matrix Composite Powder by Mechanochemical Process (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: TiN particulate/Ti5Si3 matrix composite powder has been synthesized from Ti and Si3N4 powders employing high-energy ball milling. The milled powders have been characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. TiN/Ti5Si3 composite powder is formed by a displacement reaction between Ti and Si3N4 during milling, and the reaction progresses in a mechanically induced self-propagating reaction form. The milled powder consists of TiN crystallites of a few hundred nanometers embedded in Ti5Si3 matrixes. After 20 h of milling, the crystallite size of TiN becomes about 5 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06330.x
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  • 15
    Electronic Resource
    Electronic Resource
    Depth-Profiling of Crystal Structure, Texture, and Microhardness in a Functionally Graded Tooth Enamel (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The graded nature of crystal structure, texture, and microhardness of human enamel has been characterized by grazing-incidence synchrotron radiation diffraction and Vickers indentation. Results show that the composition of tooth enamel consists mainly of calcium apatite or hydroxyapatite (HAP). The HAP crystals formed near the occlusal surface are aligned approximately orthogonal to each other between the axial and occlusal sections. In addition, the tooth enamel has been shown to be a hierarchical graded biomaterial with a distinct gradation in crystallinity, texture, crystallite size, and hardness, which is somewhat akin to that of the fibrous microstructures found in natural plants. A “graded-interface” approach is proposed as a biomimetic model for designing new dental or restorative materials as well as for joining of dissimilar materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06369.x
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  • 16
    Electronic Resource
    Electronic Resource
    Insulating Properties of Lanthanum-Doped BaTiO3 Ceramics Prepared by Low-Temperature Synthesis (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Samples of composition Ba1−xLaxTi1−x/4O3, x= 0, 0.003, 0.03, and 0.10, were prepared by an alkoxide sol–gel route with final firing of ceramics at 1100°C, 2 h in air. All samples showed bulk insulating behavior with no evidence of semiconductivity caused by either direct donor doping or oxygen loss.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06370.x
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  • 17
    Electronic Resource
    Electronic Resource
    Mechanical and Biological Performance of Calcium Phosphate Coatings on Porous Bone Scaffold (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Composite coatings, consisting of calcium phosphate (CaP) ceramics and phosphate-based glass (P-glass), were obtained on a strong ZrO2 porous scaffold to improve biocompatibility by combining mechanical properties and biological activity. Powder mixtures of hydroxyapatite (HA) and P-glass in varying composition and content were dip-coated on a ZrO2 porous scaffold and heat-treated above 800°C for 2 h in air. During thermal treatment, substantial reaction and crystallization occurred, resulting in coating phases of HA, tricalcium phosphate (TCP), dicalcium phosphate (DCP), and surrounding glass. The CaP-glass coating layer was highly dense and uniform and adhered firmly to the ZrO2 scaffold. The adhesion strength of the coating layer as tested on a nonporous disk increased with increasing glass addition and decreasing CaO content in glass. The highest strength was about 40 MPa, an improvement of twice as high as that of pure HA coating. The osteoblastic cells grew and spread actively through the coated scaffolds. The differentiation of cells on the CaP coatings was much higher than that on ZrO2 substrate and comparable to or slightly higher than that on pure HA coating.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06371.x
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  • 18
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    Influence of Microstructure Evolution on the Electroconducting Behavior of Intragranular TiN/ZTM Nanocomposites (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Electroconductive zirconia-toughened mullite (TiN/ZTM) intragranular nanocomposite was fabricated by hot-pressing a powder mixture of nano-sized TiN, ZrO2(2Y), and mullite gel. The material showed a good sinterability and could be highly densified at a low temperature of 1300°3C. Sintering temperature strongly influenced the microstructure and electrical resistivity of the material. The electrical resistivity increased monotonously from 20 Ω-cm to 1.5 times 106°3Cm, as the sintering temperature was increased from 1300° to 1500°3C. TEM results indicated that such a phenomenon could be ascribed to the changes in the microstructure of the material, which led to a decrease in the connectivity of the TiN network in the sample as the sintering temperature was increased.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00162.x
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  • 19
    Electronic Resource
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    Effects of Fluids on the Simulated Clinical-Dental Machining of a Glass Ceramic (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Effects of fluids on material removal rate, chipping damage, and surface roughness in the simulated clinical-dental machining of a dental-type glass ceramic were investigated. Significant differences in removal rate were obtained among the fluids investigated, but only a 4 wt% boric acid solution gave a higher removal rate than conventionally used water. Chipping damage was substantially lower for the boric acid and an oil-emulsion coolant compared with other fluids tested. Surface roughness was independent of the fluids used. The results indicate that improvement can be achieved in both material removal rate and machining damage by the appropriate selection of coolant chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00173.x
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  • 20
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    Measuring Permeability of Rigid Materials by a Beam-Bending Method: V, Isotropic Rectangular Plates of Cement Paste (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Beam bending is an excellent method for measuring low permeabilities (≤10−18 m2) in homogeneous materials, because it is fast, requires no high pressure, and provides a concurrent measurement of the modulus of the material. The method was previously analyzed and substantiated for cylindrical or square beams. Recently, the analysis was extended to include isotropic and transversely isotropic rectangular beams. In this paper, the analysis is applied to measurements performed on cement paste, and it is shown that the solution for isotropic rectangular beams accounts for changes in the hydrodynamic behavior caused by changing the aspect ratio of the sample. The permeability and elastic modulus results are verified through comparison to previous measurements on cylindrical beams.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06342.x
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  • 21
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    Mechanical Strength and Microstructure of Zinc Oxide Varistor Ceramics (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: ZnO-based varistor ceramics were sintered under various conditions to optimize their mechanical strength. For highest strength, the optimum sintering temperature was 1070°C or below. At higher maximum temperature, the strength decreased because of grain coarsening and the increasingly inhomogeneous distribution of secondary phases thereby induced. Fracture typically started from holes associated with hollow or poorly compacted sprayed granules. All series contained the same type of critical flaws, but, depending on the sintering temperature, the fracture toughness changed, which led to different strengths. At sintering temperatures above 1050°C, the density started to decrease slightly because of swelling attributed to the pressure of gas entrapped in closed pores.
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  • 22
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    Microstructural Variation in Porcelain Stoneware as a Function of Flux System (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fired microstructures of standard porcelain stoneware tile and tile made from mixes containing waste glass as part of the flux system were studied by XRD, SEM, and TEM. The standard porcelain stoneware microstructure consists of 100–1000 μm long mullite needles, feldspar relics, and partially dissolved α-quartz embedded in a glassy matrix. The use of soda–lime–silica (SLS) glass in the flux system led to crystallization of plagioclase, wollastonite, and sodium silicates. CaO-rich areas adjacent to quartz particles, as a result of interactions between SLS glass and silica from the quartz, and eutectic morphologies, revealed that SLS glass accelerated liquid formation and thus sintering and densification. Formation of these additional phases led to lower levels of quartz, mullite, and Na-feldspar in the microstructure although lower firing temperatures could be used to achieve full density due to generation of more fluid liquid. Use of PbO-containing waste glasses had little effect on the microstructure compared with standard composition while use of mixed PbO-containing and SLS glasses led to microstructures containing plagioclase but to lower extent than in tile with higher levels of SLS.
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  • 23
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    Hydroxyapatite Coating on Titanium Substrate by the Sol-Gel Process (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydroxyapatite coatings on titanium were attempted by a sol-gel process combined with conventional heat treatment and with UV irradiation at ambient temperature after dipping/ withdrawing a substrate into/from the sol. X-ray diffraction data showed that a coating film prepared by heat treatment was amorphous and crystallized in Ca5(PO4)3(OH) at a temperature of 773–973 K. The infrared spectra for coating films that have been prepared by heat treatment at a temperature of 573–873 K were in fair agreement with those for a coating film prepared by UV irradiation. After ethylene oxide sterilization, the cytotoxicity of coating film decreased with increasing irradiation time in UV irradiation, whereas it decreased with increasing temperature in conventional heat treatment. In comparisons between ethylene oxide sterilization and autoclave sterilization, the coating film sterilized by autoclave had much lower cytotoxicity than that sterilized by ethylene oxide. Furthermore, an animal test in the transfemoral drill hole on a rat for 4 weeks was examined using an implant prepared by heat treatment and autoclave sterilization. The sol-gel-coated titanium had slightly higher bone apposition than uncoated titanium as a control material.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb19940.x
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  • 24
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    Advances in Manufacturing Boron Carbide-Aluminum Composites (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An infiltration method for preparing a boron carbide-aluminum (B4C-AI) composite was modified so as to reduce the processing temperature and time. Titanium metal and titanium-based compounds were added to B4C powders to enhance the wettability of the liquid aluminum on boron carbide skeletons. As expected, the time required for infiltration was significantly reduced on using the additives. Of these additives titanium metal was the most effective in facilitating aluminum infiltration. Another method, involving the heat treatment of boron carbide compacts at 1300°3C for 1 h before infiltration, was attempted, and a significant improvement was gained. These findings show that the treatment modified the surface condition of boron carbide powders via the removal of oxides. An additional attempt was made to increase the boron carbide content of the system by using a bimodal powder mixture. A maximum green density of 78% was achieved by mixing fine particle size and coarse particle size powders. The infiltrated boron carbide composites prepared using a bimodal powder with a preinfiltration heat treatment of the compacts exhibited promising mechanical properties, such as a Vickers hardness (HV) of 11 Gpa and an indentation toughness (KIC) in the range of 5–7.5 MPa·m1/2.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00047.x
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  • 25
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    Spectral Imaging Analysis of Interfacial Reactions and Microstructures in Brazing of Alumina by a Hf-Ag-Cu Alloy (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A 59Ag-40Cu·1Hf (at.%) alloy that was heated on 99.6% alumina for 30 min at 1000°3C in gettered Ar melted, spread, and adhered when cooled to room temperature. Conventional scanning electron microscopic analysis with energy dispersive X-ray spectroscopy (SEM/EDXS) did not detect any reaction products at the interface. Automated X-ray spectral image analysis of the interface region revealed small pockets of a phase containing Hf and O with a stoichiometry equivalent to HfO2. Samples for transmission electron microscopic (TEM) analysis were cut to include specific HfO2 particles using focused ion beam (FIB) milling. TEM images showed that the particles were 10 to 100 nm in diameter and embedded in the alumina grains at the interface with the alloy. Based on the measured stoichiometry, electron diffraction analysis in the transmission electron microscope, and a standard Gibbs energy of reaction of ΔG°= -203.3 kJ at 1300 K for the reaction 3Hf + 2Al2O3→ 3HfO2+ 4Al, the particles are judged to be HfO2 that formed from simple redox reaction between Hf and Al2O3.
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  • 26
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    Processing of Lithium Zirconate for Applications in Carbon Dioxide Separation: Structure and Properties of the Powders (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Lithium zirconate, Li2ZrO3, has been reported as a candidate material for high-temperature CO2 separation. The reaction of Li2ZrO3 with CO2 is extremely fast, and the material can store significant quantities of CO2 at high temperature. The reacted CO2 can be regenerated by thermal cycling. Alternatively, a membrane system might be developed based on the reversible reaction process. For absorption and membrane separation, the particle size, crystal structure, and state of agglomeration of the Li2ZrO3 powders are important. Therefore, we have synthesized Li2ZrO3 using sol-gel procedures and compared its properties with powders made via a powder-mixing route and a commercial-grade powder. The morphologic and structural characteristics of the powders and their CO2 absorption properties are discussed.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00068.x
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  • 27
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    Effect of Core Materials on the Formation of Hollow Alumina Microspheres by Mechanofusion Process (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Core/shell structures have been prepared via a mechanofusion system by employing several kinds of spherical polymers as a core material and Al2O3 powder or a mixture of Al2O3 and SiO2 powders as a shell material. The effect of the kind of core polymers on the quality of the resulting hollow alumina microspheres has been discussed on the basis of the thermal decomposition behavior of spherical polymers used as a core material. A large fraction of hollow alumina microspheres reflecting the shape and the particle size distribution of the core polymer could be fabricated after sintering at 1600°3C for 3 h, when highly cross-linked poly(methyl methacrylate) (PMMA) microspheres with a gel fraction of 99.03% were used as a core polymer, and abrupt firing at temperatures higher than 500°3C was adopted to remove the PMMA microspheres. The addition of 5 mass% SiO2 to the Al2O3 shell layer was found to be useful for maintaining the spherical shell structure during the firing process and for fabricating a large fraction of hollow alumina microspheres after the sintering.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00060.x
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  • 28
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    Synthesis of Silicon Nitride from Carbothermal Reduction of Rice Husks by the Constant-Rate-Thermal-Analysis (CRTA) Method (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Silicon nitride (Si3N4) has been obtained from the carbothermal reduction of rice husks by applying the constant-rate-thermal-analysis (CRTA) method. Under this method, the reaction rate of carbothermal reduction can be controlled and at the same time the CO concentration generated is maintained constant at a previously selected value by the user. By using this synthesis technique it has been possible to obtain ceramic powder from rice husks with a determined phase composition and a controlled microstructure. Therefore, rice husks have great potential as a raw material for producing Si3N4 by the CRTA method.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00075.x
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  • 29
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    Effect of a Boron Nitride Interphase That Debonds between the Interphase and the Matrix in SiC/SiC Composites (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Typically, the debonding and sliding interface enabling fiber pullout for SiC-fiber-reinforced SiC-matrix composites with BN-based interphases occurs between the fiber and the interphase. Recently, composites have been fabricated where interface debonding and sliding occur between the BN interphase and the matrix. This results in two major improvements in mechanical properties. First, significantly higher failure strains were attained due to the lower interfacial shear strength with no loss in ultimate strength properties of the composites. Second, significantly longer stress-rupture times at higher stresses were observed in air at 815°3C. In addition, no loss in mechanical properties was observed for composites that did not possess a thin carbon layer between the fiber and the interphase when subjected to burner-rig exposure. Two primary factors were hypothesized for the occurrence of debonding and sliding between the BN interphase and the SiC matrix: a weaker interface at the BN/matrix interface than the fiber/BN interface and a residual tensile/shear stress-state at the BN/matrix interface of melt-infiltrated composites. Also, the occurrence of outside debonding was believed to occur during composite fabrication, i.e., on cooldown after molten silicon infiltration.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00104.x
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  • 30
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    Effect of Acceptor and Donor Dopants on the Dielectric and Tunable Properties of Barium Strontium Titanate (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effects of different concentrations of Mn2+, Mg2+, Al3+, Fe3+, La3+, and Nb5+ on the dielectric and tunable properties of Ba0.6Sr0.4TiO3 ceramics were investigated. It was found that doping in small amounts with acceptor ions such as Mg2+, Fe3+, and Al3+ could meliorate the dielectric properties clearly. Decrease of dielectric loss was attributed to the formation of compensating defects originating from acceptor substitution. It was concluded that the tunability was linked to both the dielectric constant and the grain size. A higher figure of merit was obtained by doping the ceramics with smaller ions of Al and Fe, compared to Ti.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07494.x
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  • 31
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    Nickel–Alumina Functionally Graded Materials by Electrophoretic Deposition (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Electrophoretic deposition has been used to synthesize nickel–alumina, functionally graded materials from NiO and alumina suspensions in ethanol. Suspension stability and the kinetics of deposition were studied to determine optimum conditions. Deposition starts with an alumina suspension into which a stream of NiO suspension is injected at various flow rates to obtain the desired profiles. The latter were controlled by varying the deposition current density and component flow rate. The green bodies obtained were sintered in Ar/H2 atmosphere to reduce the NiO to nickel. Various gradation profiles were obtained illustrating the facility of EPD to synthesize continuously graded materials. NiO was used as the precursor for nickel to alleviate settling and rough columnar deposit problems.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06359.x
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  • 32
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    Synthesis of Ordered Zirconium Titanate (Zr,Ti)2O4 from the Oxides Using Fluxes (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The crystallization of ordered (Zr,Ti)2O4 from the oxides succeeded for the first time, at 800°–1200°C and 13–20 kbar, using either ammonium carbonate or copper oxide as flux. The composition of the ordered phase, coexisting with either zirconia or rutile, is pressure–temperature dependent, ranging from XTi= 0.60 to 0.68. Its reproducibility and reversibility suggest the ordered compound crystallized at/near thermodynamic equilibrium. The presence of flux permits the equilibration of phase assemblages well below 1200°C, a region previously inaccessible for equilibrium experiments in the ZrO2–TiO2 system due to sluggish kinetics. Thus we were able to determine the ZrO2–TiO2 phase diagram at 20 kbar at temperatures as low as 800°C. In contrast, room-pressure experiments did not result in the spontaneous nucleation of ordered (Zr,Ti)2O4 from the oxides, and seeds were required to initiate growth. The flux-aided synthesis of ordered (Zr,Ti)2O4 from the oxides, at constant temperature and in its stability field, has the following advantages over previous crystallization attempts, which consisted of slow cooling of the disordered polymorph through the ordering transition. The ordered compound forms at equilibrium, therefore permitting phase equilibrium studies and thermodynamic interpretation. Large grain sizes facilitate quantitative analysis of the composition with electron microscopy. Microcracks and ZrO2 exsolution, reported from samples cooled through the transition, can be avoided. The composition and the ordering state of the ordered compound can be controlled with pressure and temperature. Using the flux-based synthesis method, well-crystallized samples can now be obtained for future crystal structure refinements, calorimetric and dielectric measurements, or investigations into the phase transition.
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  • 33
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    Aluminum Phosphates Derived from Alumina and Alumina-Sol–Gel Systems (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Aluminum phosphate products formed by the reactions of alumina and alumina-gel systems with acidic phosphates were analyzed. Drying of alumina-gel to form microcrystalline boehmite and conversion to γ-alumina by thermal treatment was indicated by the appearance of octahedral, pentacoordinate, or tetrahedral sites, which were established using 27Al magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Crystalline aluminum phosphate products and amorphous material were identified using this technique. α-alumina and heat-treated alumina-gel that were reacted with phosphate in an Al:P ratio of 1:1 yielded dramatically different aluminum orthophosphate:aluminum metaphosphate product ratios of 8.2:1 and 1:1.1, respectively. When alumina-gel was heat-treated with phosphate, an abundance of aluminum orthophosphate, aluminum metaphosphate, and hydrated aluminum phosphate products were affected by varying conditions of temperature and time of heat treatment and by the amount of phosphate present. An α-alumina/alumina-gel composite sol–gel phase that was reacted with phosphoric acid (H3PO4) in a Al:P ratio of 1:1 exhibited an increased quantity of aluminum metaphosphate products compared with an α-alumina:H3PO4 ratio of 1:1 and a higher percentage of reaction (79%) compared with the reactions of an α-alumina:H3PO4 ratio of 1:1 or an alumina-gel:H3PO4 ratio of 1:1. The morphologies of aluminum triphosphate hydrate and aluminum metaphosphate product phases were observed using scanning electron microscopy.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06361.x
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  • 34
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    Synthesis of Ba(Mg1/3Ta2/3)O3 Microwave Ceramics through a Sol–Gel Route Using Acetate Salts (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A sol–gel process to unsophisticatedly synthesize Ba(Mg1/3Ta2/3)O3 (BMT) ceramics at low cost has been developed in the present work. This process involves the reaction of TaCl5 with acetates of Ba and Mg in the presence of citric acid. Pure BMT polycrystalline powders can be obtained by calcining the synthesized products at 1000°C. The BMT powders were found to have a primary particle size as small as 100 nm. BMT ceramics with favorable structural characteristics can be obtained from sintering of the sol–gel BMT at temperatures much lower than that for the conventional solid-state BMT. Sintering the sol–gel BMT in pellet form at 1300°C resulted in an ordering parameter of 0.72 for the pellet, and a relative density of 〉95% was achieved with sintering at 1500°C. The grain size of the sintered sol–gel BMT was large and uniform in comparison with the products from the solid-state method. Using the sol–gel route, sintering at temperatures as low as 1400°C gave ceramics with acceptable microwave dielectric properties (a dielectric constant of 16 and Qf factor of 14 400 GHz), while higher temperatures (〉1600°C) are needed for the solid-state route to give similar properties.
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  • 35
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    Mechanism for Developing the Boundary Barrier Layers of CaCu3Ti4O12 (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: CaCu3Ti4O12 (CCTO) was prepared by solid-state reaction and identified by X-ray diffractometry. The evolution of the microstructure was observed by scanning electron microscopy (SEM). It was found that discontinuous grain growth developed during sintering, and large abnormal grains played a very significant role in the dielectric behavior. Cu ions segregated to the boundaries and CuO located at the triple-point sites of the abnormal large grains were observed by electron energy loss and energy-dispersive X-ray spectroscopy, respectively. Moreover, two kinds of morphologies, i.e., terraces with ledges and bump domains, were discovered inside the grains under the thermal etching conditions at 960°C for 72 min, which solves the contradiction related to the interpretation of the giant dielectric response between ceramic and single-crystal CCTO. Complex impedance spectroscopy was used to analyze the conductivity of ceramic CCTO, which suggests that it consists of conducting domains with two kinds of insulating barrier layers of domain and grain boundaries. The insulating domain and grain boundaries were attributed to orderly arranged dislocations and segregation of Cu ions, respectively. The conduction of CCTO was found to be related to the porosity, the grain size, and the thickness of the insulating boundary layers. For a sample sintered at 1065°C for 3 h, the anomalously low resistivity and temperature-dependent dielectric constant were due to the fact that domain boundaries were not substantially formed. The possible reasons for the development of barrier layers and the variation of the dielectric constant with the sintering time are discussed. A barrier-layer model with dielectric response based on the Maxwell–Wagner type of relaxation for ceramic CCTO is proposed. Two kinds of dielectric responses occur, depending on the microstructure: they are dominated by the domain and domain boundary and by the grain and grain boundary for large grains and fine grains, respectively.
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  • 36
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    Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3–Pb(Zr/Ti)O3 Relaxors (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The structure and dielectric properties of (1−x)Pb(Sc2/3W1/3)O3–(x)Pb(Zr/Ti)O3 ceramics have been investigated over a full substitution range. All compositions with x 〈 0.5 adopt a cubic perovskite structure; however, for x≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc2/3W1/3)O3 (PSW) can be described by a random-site model with one cation site occupied by Sc3+ and the other by a random distribution of (Sc1/33+W2/36+). The ordering is destabilized in solid solutions of PSW with PbZrO3 (PSW–PZ), but stabilized by PbTiO3 in the (1−x)PSW–(x)PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum (Tɛ,max) increases linearly with x; however, for PSW–PT Tɛ,max decreases in the ordered region (up to x= 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, Tɛ,max increased by more than 60°C.
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    Cement Composition Effects on the Rheological Property Evolution in Concentrated Cement–Polyelectrolyte Suspensions (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied the rheological property evolution and hydration behavior of white and ordinary portland cement (type I) pastes and concentrated cement–polyelectrolyte suspensions. Cement composition had a marked effect on the elastic property evolution (G′(t)) and hydration behavior of these suspensions in the presence of poly(acrylic acid)/poly(ethylene oxide) copolymer (PAA/PEO), even though their affinity to adsorb such species was nearly identical. Both white and ordinary portland cement pastes exhibited G′0 values of ∼104 Pa and fully reversible G′(t) behavior until the onset of the acceleratory period (t= 2 h), where the pastes stiffened irreversibly. In contrast, cement–PAA/PEO suspensions exhibited G′0 values of ∼1 Pa and G′(t) behavior comprised of both reversible and irreversible features. Interestingly, ordinary portland cement–PAA/PEO suspensions experienced a gel-to-fluid transition on high shear mixing at short hydration times (〈1 h), and the particle network did not rebuild until ∼24 h of hydration. In sharp contrast, white portland cement–PAA/PEO suspensions remained weakly gelled throughout the initial stage of hydration even after high shear mixing. At longer hydration times (〉1 h), both cement–PAA/PEO suspensions exhibited G′i(t) ∼ exp(t/τc) with τc values of 5.6 and 1.3 h for ordinary and white portland cement, respectively. Our observations suggest that hydration phenomena impact interparticle forces during early stage hydration and, ultimately, lead to initial setting through the formation of solid bridges at the contact points between particles within the gelled network.
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  • 38
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    New Freeze-Casting Technique for Ceramics with Sublimable Vehicles (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new ceramic freeze-casting technique capable of manufacturing near room temperature with a sublimable vehicle was accomplished. Fluid-concentrated slurries of Al2O3 powder in molten camphene (C10H16) were prepared at 55°C. These slurries were quickly solidified (frozen) at room temperature to yield rigid solid green bodies, followed by frozen camphene removal by sublimation (freeze-drying) with negligible shrinkage. Sintering without any special binder burnout process yielded sintered bodies with over 98% theoretical density. The proposed advantages include (1) elimination of extremely cold temperatures, (2) elimination of troublesome binder burnout process, and (3) fast manufacturing cycle due to quick solidification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06331.x
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    Geometry and Electrical Properties of Grain Boundaries in Manganese Zinc Ferrite Ceramics (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: For large-grained manganese zinc (MnZn) ferrite ceramics, grain misorientation determined by electron backscatter diffractions and grain-boundary resistance measured using microcontact impedance spectroscopy have been correlated. The degree of oxidation of grain boundaries and, hence, the barrier height depends on the overall grain-boundary network as well as on the individual boundary structure; therefore, a statistical analysis has been performed based on several hundreds of local measurements. When the boundaries are divided into low- and high-resistance groups, statistically significant differences in rotation axis and angle distributions are found. The misorientation distribution of the low-resistance boundary group is suggested to reflect the low-energy configurations of boundary planes in MnZn ferrites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06337.x
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  • 40
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    Sol–Gel Preparation and Properties of Fluoride-Substituted Hydroxyapatite Powders (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) powders were synthesized by a sol–gel method for usage as bone filler and drug carrier. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol–water-based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of FHA powders. With heat treatment above 400°C, a characteristic apatite phase was observed for all the sol–gel powders. However, the crystallization temperature decreased with increasing fluoride addition. The tricalcium phosphate (TCP) phase formed in the pure HA powder above 800°C was attenuated in the FHA powders, confirming an enhanced phase stability of the FHA powders. Increasing the F− addition improved crystallinity and increased the crystallite size, as was determined from X-ray diffraction (XRD) analyses. The lattice parameters of the heat-treated powders varied corresponding to the fluoride addition, i.e., a gradual decrease in the a-axis, while little change in the c-axis was observed with increasing fluoride addition, indicating a nearly complete substitution of fluoride within the apatite lattice. However, little difference was observed with heat-treatment temperatures (400°–1000°C). The powders substituted with fluoride exhibited reduced dissolution rates in an in vitro solution as compared with the pure HA powder, suggesting the possibility of tailoring bioactivity with fluoride substitution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06344.x
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  • 41
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    Crystal Structure and Thermal Expansion of La1−xSrxFeO3−δ Materials (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Crystal structure and thermal properties of La1−xSrxFeO3−δ (x= 0, 0.1, 0.3, 0.4, 0.5, and 0.75) have been studied by high-temperature X-ray diffraction and thermal analysis in air and nitrogen (p(O2) ∼ 10−3 atm) atmosphere. The first-order phase transition from orthorhombic-to-rhombohedral La1−xSrxFeO3−δ (x= 0, 0.1) was strongly shifted to lower temperatures with increasing Sr content. The phase-transition temperature was observed significantly lower in polycrystalline ceramics compared with fine powders. The temperature depression of the phase transition in the ceramics was qualitatively explained by stresses induced both by the anisotropic thermal expansion of LaFeO3 and the observed volume contraction of the phase transition. Rhombohedral La1−xSrxFeO3−δ (x= 0.3, 0.4, 0.5) were observed to transform to the cubic perovskite structure during heating. The second-order phase-transition temperature decreased with increasing Sr content and decreasing partial pressure of oxygen. On the basis of the present findings, a pseudobinary phase diagram of the LaFeO3–SrFeO3−δ system is presented. Finally, a severely nonlinear thermal expansion was observed for the Sr-rich materials at high temperature. The high thermal expansion in this region is due to a chemical expansion resulting from a reduction of the valence state of Fe.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06346.x
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  • 42
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    Phase Relations and Thermal Expansion Studies in the Ceria–Yttria System (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1–xYxO2–x/2 (0.0 ≤x≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the αl (293–1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, αa (293–1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1–xYxO2–x/2 (0.0 ≤x≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1–xYxO2–x/2 (0.0 ≤x≤ 1.0), because CeO2 is widely used as a surrogate material for PuO2.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06349.x
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  • 43
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    Zirconia–Silica–Carbon Coatings on Ceramic Fibers (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Precursors for zircon–carbon mixtures were made to coat fibers for ceramic-matrix composites. Precursors were characterized using XRD, TGA, and DTA. Zircon formed from vanadium- or lithium-doped precursors after heat treatments at ≥900°C in air, but it did not form at 1200°–1400°C in argon when large amounts of carbon were added. Some precursors were used to coat Nextel™ 720 and Hi-Nicalon™ fibers. The coatings were characterized using SEM and TEM, and coated-fiber tensile strengths were measured. Although zircon formed in powders, only tetragonal-zirconia–silica mixed phases formed in fiber coatings at 1200°C in air. Loss of vanadium oxide flux to the fibers may have caused the lack of conversion to zircon. The strengths of the coated fibers were severely degraded after heat treatment at ≥1000°C in air, but not in argon. The coated fibers were compared with zirconia–carbon-coated fibers made using similar methods. Mechanisms for fiber strength degradation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06348.x
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  • 44
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    Structural Characterization of Lanthanum Chromite Perovskite Coating Deposited by Magnetron Sputtering on an Iron-Based Chromium-Containing Alloy as a Promising Interconnect Material for SOFCs (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Chromium-containing stainless steel (SS) is a prospective material for use as an interconnect in solid oxide fuel cells (SOFCs). However, during operations at high temperatures, the growth of oxide scales causes the performance of the interconnect and SOFC as a whole to deteriorate. The coating of SS 446 with a conducting perovskite is a potential method of slowing the growth of oxide scale and, therefore, improving overall SOFC performance. In the present research, the structural characterization of a pure LaCrO3 thin film on the SS 446 substrates has been performed as a model material that can be used as a barrier coating for the metallic interconnect. The deposition of an amorphous La-Cr-O thin film on SS 446 was performed using radio-frequency (rf) magnetron sputtering. The deposited amorphous film was annealed in air to form the desired perovskite phase. The film underwent an amorphous to LaCrO4 phase transition during annealing at 500°C with further transformation to LaCrO3 orthorhombic phase during annealing at 700°C. A self-organized dendritic structure was reported as a result of the perovskite-phase formation. Although formation of various oxides, such as Fe2O3 and Fe3O4, was observed during the annealing of uncoated SS 446 in air, the coating of SS 446 surface with LaCrO3 film prevented formation of various oxide phases at the interconnect surface. The structural characterization of the films and SS 446 surfaces was accomplished using scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffractometry, micro-Raman spectroscopy, and nanoindentation.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06350.x
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  • 45
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    Effect of Interparticle Potential on Forming Solid, Spherical Agglomerates during Drying (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of the interparticle potential on the shapes of the agglomerates obtained by drying slurry droplets has been investigated using aqueous alumina slurries formulated in the dispersed and weakly attractive (dispersed + added salt) states. For the dispersed slurry, the droplets dried to irregular shapes with hollow centers. When just the right amount of salt was added to produce an attractive, but nontouching, particle network, the droplets dried as solid spheres. These results are discussed by relating both the nature of the particle network (repulsive or weakly attractive), the slurry rheology, and the consolidation mechanics of the networks to the requirements for maintaining a spherical geometry and uniform density during droplet drying.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb19936.x
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  • 46
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    Direct Formation of Iron(III)-Doped Titanium Oxide (Anatase) by Thermal Hydrolysis and Its Structural Property (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Anatase-type TiO2 (titania) doped with iron up to 19.8 mol% was directly formed as nanometer-sized particles from acidic precursor solutions of TiOSO4 and Fe(NO3)3 by simultaneous hydrolysis, under mild hydrothermal conditions at 180°3C. Iron content in the anatase-type TiO2 was much less than that of the starting composition of the precursor solutions because of slower hydrolysis rate of Fe(NO3)3 than that of TiOSO4 at 180°3C. The XRD data, TEM selected-area diffraction patterns, and Mössbauer effect measurement showed that iron(III) formed a solid solution in the anatase-type TiO2 precipitates and that there was no iron oxide precipitated as secondary phase without making a solid solution with TiO2 present in the precipitates. Doping of Fe2O3 into TiO2 shifted the phase transformation from anatase-type to rutile-type structure to a low temperature. On the phase transformation from anatase to rutile, iron oxide was precipitated as Fe2TiO5 (pseudobrookite) phase. When the iron content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400–600 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Fe(III)-doped TiO2.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb19941.x
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  • 47
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    Producing Ceramic Foams with Hollow Spheres (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ceramic foams have a large potential for many applications and can be produced in several ways. In the past, many have attempted to manufacture ceramic foams that combined sufficient strength and controlled microstructure. This study proposes a new two-step processing route to fulfill these requirements. First, sacrificial cores are coated with ceramic powder slurry and packed in a die. Second, the cores are connected together using another ceramic slurry coating. After they are burned out and sintered, ceramic foam structures can be obtained that have a density 〈10% of theoretical density. By varying the size and shape of the initial cores, ceramic foams with tailor-made microstructures can be easily produced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb19965.x
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  • 48
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    Microstructural Studies on the Low-Temperature Crystallization Process of Strontium Bismuth Tantalate Thin Films (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The preparation of strontium bismuth tantalate (SBT) thin films at low temperatures for electronic applications is at present the subject of intense study. However, the microstructural evolution of these films has not been extensively reported, despite its importance in the determination of the final properties of the film. In this work, we study SBT thin films with various nominal compositions obtained by the crystallization at 650°3C of spin-coated solutions on a silicon-based substrate. Both the formation of the perovskite phase and the evolution of the grains are analyzed, with special attention to the formation of platelet-like grains. A process of coalescence of initially round grains is proposed to explain the grain growth in this system. We also show that the use of a preannealing step inhibits the grain growth and, therefore, should be avoided. The role that the film thickness plays in the development of large grains is discussed.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00138.x
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  • 49
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    Monolithic t-ZrO2 Nanopowder through a ZrO(OH)2·xH2O Polymer Precursor (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Monolithic t-ZrO2 (tetragonal structure) nanopowder is synthesized with an amorphous ZrO(OH)2·xH2O polymer precursor. The H2O molecules impart the structure and promote reconstructive thermal decomposition of the structure to t-ZrO2 nanoparticles on heating at temperatures as low as 200°C. A prevalent endothermic heat output in the dissociation process controls the local temperature in exothermic nucleation and growth of various groups of the reaction species so that it is self-controlled in high-energy nanoparticles. Crystallites are, on average, d= 8 nm diameter, and they have a high value of Gibbs free energy or lattice volume Vo= 0.06770 nm3. The excess volume decreases to Vo= 0.06705 nm3 if the reaction temperature is increased to 〉200°C, i.e., approximately the bulk value of 0.06681 nm3; there is a minor increase to d= 12 nm at 600°C. Many oxygen vacancies in the thin surface space-charge layers seem to support the stability of small particles in this particular polymorph. A pure m-ZrO2 (monoclinic structure) appears with d= 22 nm at temperature as low as 800°C. The results are analyzed using X-ray diffractometry, microstructure, infrared spectroscopy, and thermal studies of the polymer precursor and derivative t-ZrO2 nanoparticles.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07489.x
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  • 50
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    Optimization of Chemical Vapor Deposition Parameters for Fabrication of Oxidation-Resistant Mullite Coatings on Silicon Nitride (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fabrication of mullite (3Al2O3·2SiO2) coatings by chemical vapor deposition (CVD) using AlCl3–SiCl4–H2–CO2 gas mixtures was studied. The resultant CVD mullite coating microstructures were sensitive to gas-phase composition and deposition temperature. Chemical thermodynamic calculations performed on the AlCl3–SiCl4–H2–CO2 system were used to predict an equilibrium CVD phase diagram. Results from the thermodynamic analysis, process optimization, and effects of various process parameters on coating morphology are discussed. Dense, adherent crystalline CVD mullite coatings ∼2 μm thick were successfully grown on Si3N4 substrates at 1000°C and 10.7 kPa total pressure. The resultant coatings were 001 textured and contained well-faceted grains ∼0.3–0.5 μm in size.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07491.x
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  • 51
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    Chemical Processing of CaHPO4·2H2O: (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The aim of this paper is to develop a robust chemical process to synthesize Na- and K-doped brushite (DCPD: dicalcium phosphate dihydrate, CaHPO4·2H2O), a potential starting material for bone substitutes. The powders were synthesized by using sodium phosphate and potassium phosphate and aqueous solutions containing calcium chloride at room temperature, followed by drying at 37°C. DCPD powders thus formed were found to contain 460 ppm K and 945 ppm Na. On calcination in air, these powders readily transformed into monetite (DCPA: dicalcium phosphate anhydrous, CaHPO4) first, and then into Ca2P2O7 (calcium pyrophosphate). Na- and K-doped DCPD powders were shown to completely transform, in less than 1 week, into poorly crystalline carbonated apatite on immersion in an acellular simulated/synthetic body fluid (SBF) solution at 37°C. The Tris (i.e., tris(hydroxymethyl)aminomethane) buffered SBF solution used in this study had a carbonate ion concentration of 27 mM equal to that of human plasma. DCPD powders of this study displayed a notable apatite-inducing ability. This finding suggests the use of these DCPD powders as the starting materials for potential bone substitutes, which can be easily manufactured in aqueous solutions friendly to living tissues, at temperatures between room temperature and 37°C.
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    Fabrication of High-Strength Continuous Zirconia Fibers and Their Formation Mechanism Study (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Continuous zirconia fibers with a nanometer ceramic structure and a tensile strength up to 2.8 GPa were fabricated by pyrolyzing polyacetylacetonatozirconium precursor fibers through a special atmosphere heat treatment. DSC-TGA, GC-MS, IR, SEM, and TEM were used to study the fiber transformation mechanism during heating. Results showed that special atmosphere heat treatment could make the organics in the fibers come out directly without carbonization and remove them almost entirely under 400°C, and the obtained zirconia fibers had few defects, good continuity, and high strength.
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    Spark-Plasma Sintering of Silicon Carbide Whiskers (SiCw) Reinforced Nanocrystalline Alumina (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of γ-Al2O3 nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiCw/γ-Al2O3 nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (∼118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of γ-Al2O3 to α-Al2O3 of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiCw/HEBMγ-Al2O3 nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m1/2.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07510.x
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    Room-Temperature Freeze Casting for Ceramics with Nonaqueous Sublimable Vehicles in the Naphthalene–Camphor Eutectic System (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Freeze casting for Al2O3 was accomplished at room temperature with nonaqueous sublimable vehicles in the naphthalene–camphor eutectic system with a eutectic temperature of 31°C. A fully dense sintered body (〉99.5% of theoretical density (T.D.)) was obtained with a eutectic composition vehicle, whereas at most 90% T.D. was obtained with an off-eutectic (i.e., hypo- or hypereutectic) composition vehicle due to formation of large uniquely shaped voids. Microstructural observation suggested that growing pro-eutectic crystals rejected the suspended Al2O3 particles to form large voids during the solidification process. At the eutectic composition, formation of fine lamellar microstructure in a solidified vehicle is considered to inhibit particle rejection resulting in large voids.
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    Mechanochemical Synthesis of Magnesium Aluminate Spinel Powder at Room Temperature (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: MgAl2O4 spinel was successfully synthesized using a mechanochemical route that avoided the formation and calcination of its precursors at high temperatures. The method involved a single step in which γ-Al2O3–MgO, AlO(OH)–MgO, and α-Al2O3–MgO mixtures were milled at room temperature under air atmosphere. The formation of MgAl2O4 occurred faster with γ-Al2O3 than with AlO(OH) or α-Al2O3. After 140 h, the mechanochemical treatment of the γ-Al2O3–MgO mixture yielded 99% of MgAl2O4.
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    Electronic Structure and Bonding of All Crystalline Phases in the Silica–Yttria–Silicon Nitride Phase Equilibrium Diagram (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reviews the structures and properties of 10 binary, ternary, and quaternary crystals within the equilibrium phase diagram of the SiO2–Y2O3–Si3N4 system. They are binary compounds SiO2, Y2O3, Si3N4; ternary compounds Si2N2O, Y2Si2O7, and YSi2O5; and quaternary crystals Y2Si3N4O3 (M-melilite), Y4Si2O7N2, (N-YAM), YSiO2N (wallastonite), and Y10(SiO4)6N2 (N-apatite, N-APT). Although the binary compounds are well-known and extensively studied, the ternary and the quaternary crystals are not. Most of the ternary and the quaternary crystals simply have been referenced as secondary phases in the processing of nitrogen ceramics. Their crystal structures are complex and not precisely determined. In the quaternary crystals, there exists O/N disorder in that the exact atomic positions of the anions cannot be uniquely determined. It is envisioned that a variety of cation–anion bonding configurations exist in these complex crystals. The electronic structure and bonding in these crystals are, therefore, of great interest and are indispensable for a fundamental understanding of structural ceramics. We have used ab initio methods to study the structure and bonding properties of these 10 crystals. For crystals with unknown or incomplete structural information, we use an accurate total energy relaxation scheme to obtain the most likely atomic positions. Based on the theoretically modeled structures, the electronic structure and bonding in these crystals are investigated and related to various local cation–anion bonding configurations. These results are presented in the form of atom-resolved partial density of states, Mulliken effective charges, and bond order values. It is shown that Y–O and Y–N bonding are not negligible and should be a part of the discussion of the overall bonding schemes in these crystals. Spectroscopic properties in the form of complex, frequency-dependent dielectric functions, X-ray absorption near-edge structure (XANES), and the electron energy-loss near-edge structure (ELNES) spectra in these crystals also are calculated and compared. These results are discussed in the context of specific bonding configurations between cations (silicon and yttrium) and anions (oxygen and nitrogen) and their implications on intergranular thin films in polycrystalline Si3N4 containing rare-earth elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06352.x
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    Low-Temperature Hydrothermal Synthesis of Phase-Pure (Ba,Sr)TiO3 Perovskite using EDTA (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A thermodynamic model was developed to describe the stability of (Ba,Sr)TiO3 (BST) solid solutions in the Ba–Sr–Ti–K–(EDTA)–H2O (EDTA = ethylenediaminetetraacetic acid) system. Phase diagrams were computed to identify the range of conditions suitable for making phase-pure BST. Hydrothermal experiments were performed to validate the thermodynamic model. The model was found to be more useful when an ideal solid solution was used to estimate the energetics for the BST phase instead of experimental thermodynamic data. In addition, EDTA was found to promote stable conditions for BST formation. When attempting to prepare Ba0.50Sr0.50TiO3 without EDTA, BaTiO3-rich and SrTiO3-rich phases precipitated separately, at 70°–160°C. However, in the presence of EDTA, a phase-pure Ba 0.55Sr0.45TiO3 solid solution was obtained at 90°–120°C. EDTA is effective because it prevents phase heterogeneities from forming and equalizes the adsorption affinity of strontium and barium species.
    Type of Medium: Electronic Resource
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    Combustion Synthesis and Characterization of Nanocrystalline Tin and Tin Oxide (SnOx, x= 0–2) Particles (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Nanocrystalline SnOx particles (x= 0–2) were synthesized using tetramethyltin (Sn(CH3)4) vapor as the particle precursor reactant in hydrogen/oxygen/argon (H2/O2/Ar) flames. The particle composition and morphology were characterized using X-ray diffractometry, transmission electron microscopy, and nitrogen (N2) surface adsorption. By controlling the concentration of oxygen in the reactant gases and the flame temperatures, metallic tin (Sn), tin monoxide (romarchite SnO), and/or tin dioxide (cassiterite SnO2) were generated. The crystalline powders consisted of both discrete primary particles and agglomerates, with average primary particle sizes of 23–24 nm for SnO2 and 69 nm for Sn (based on specific surface area measurements of bulk powders collected in the exhaust region of the flame). The compositional results were interpreted using equilibrium and detailed chemical kinetics models.
    Type of Medium: Electronic Resource
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    Simultaneous Synthesis and Sintering of α-Ti1–xAlx(N) (0 ≤x≤ 0.08) by a Self-Propagating High-Temperature Combustion Method (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Simultaneous synthesis and sintering of hexagonal α-Ti1−x-Alx(N) (0 ≤x≤ 0.08) solid solutions, which contain a small amount of nitrogen, have been performed by a self-propagating high-temperature combustion method under a nitrogen pressure of 4 MPa. Dense materials (∼99% of theoretical) prepared directly from a mixture of elemental (Ti and Al) powders reveal homogeneous microstructure composed of fine grains (12–16 μm). α-Ti1−xAlx(N) (x= 0.02; Ti0.98Al0.02N0.26) exhibits a three-point bending strength σb of 390 MPa, a Vickers hardness Hv of 9.24 GPa, and a fracture toughness KIC of 4.89 MPa·m1/2; their mechanical properties are much improved by doping Al into α-Ti(N), in comparison with those (σb= 245 MPa, Hv= 9.02 GPa, and KIC= 3.77 MPa·m1/2) of α-Ti(N) fabricated under the same conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06357.x
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  • 60
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    Mechanical Properties of Textured Alumina Made by High-Temperature Deformation (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanical properties of a textured alumina made by high-temperature deformation of normal-purity sintered alumina have been investigated. The textured alumina shows very high bending strength and extremely high fracture toughness. Fracture toughness of more than 10 MPa·m1/2 was measured by the single-edge precracked beam method, and even using the single-edge V-notched beam method, toughness of over 8 MPa·m1/2 was obtained. This high fracture toughness was attributed to a large number of aligned small platelike grains of the textured structure enhancing the grain bridging effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06374.x
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    Porous Electrodes for Low-Temperature Solid Oxide Fuel Cells Fabricated by a Combustion Spray Process (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new combustion spray process has been developed for depositing films and coatings from particles (or particulate materials) suspended in a flammable liquid. The suspension is pumped to an atomizer to produce a mist of the droplets, which is then ignited to create a combustion flame. The solid particles are thermally activated for formation of films and coatings on a substrate inserted into or near the flame. Solid oxide fuel cells (SOFCs) with porous electrodes fabricated by combustion spray show better performance than those prepared by other fabrication processes (such as conventional dry-pressing and firing) especially at low operating temperatures.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06372.x
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    Microstructures and Microwave Dielectric Characteristics of CaRAlO4 (R = Nd, Sm, Y) Ceramics with Tetragonal K2NiF4 Structure (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: CaRAlO4 (R = Nd, Sm, Y) ceramics with a K2NiF4 structure were prepared by a solid-state reaction approach, and their microwave dielectric characteristics were evaluated, along with their microstructures. Dense CaNdAlO4, CaSmAlO4, and CaYAlO4 ceramics were obtained by sintering at 1425°–1500°C in air for 3 h, and good microwave dielectric characteristics were achieved: (1) ɛ= 18.2, Qf= 17 980 GHz, τf=−52 ppm/°C for CaNdAlO4; (2) ɛ= 18.2, Qf= 51 060 GHz, τf=−3 ppm/°C for CaSmAlO4; and (3) ɛ= 18.9, Qf= 39 960 GHz, τf= 6 ppm/°C for CaYAlO4.
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    CORRECTION (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06375.x
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    Determination of the Thermal Resistance of the Polymer–Ceramic Interface of Alumina-Filled Polymer Composites (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: To model the thermal conductivity of polymer composites that are filled with ceramic powders, the conductivity of each component as well as the interfacial resistance at each ceramic–polymer boundary must be known. An indirect method to determine this interfacial boundary resistance is proposed by preparing large-scale “macromodel” simulations of the polymer–ceramic interface. Macromodels, prepared by spin-coating a polymer layer onto sapphire wafers, were formed in a sapphire–polymer–sapphire sandwich type structure. The interfacial boundary thermal resistance was calculated from thermal resistance measurements made on the macromodels.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06326.x
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    Oxygen Diffusion in Yttria-Stabilized Zirconia: A New Simulation Model (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We present a multiscale modeling approach to study oxygen diffusion in cubic yttria-stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long-time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation-dopant-induced correlation effects in support of the above explanation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06325.x
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    Critical Factors Affecting the Wettability of α-Alumina by Molten Aluminum (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The wetting behaviors of α-Al2O3 single crystals with three different faces—R(0112), A(01120), and C(0001)—and polycrystals (PC) by molten aluminum were studied over a wide temperature range using both a conventional and an improved sessile-drop method. The critical factors affecting the wettability, such as temperature, atmosphere, substrate surface roughness, and crystallographic orientation, and the influence from the experimental technique, were thoroughly investigated. The results show that the aluminum surface oxidation and the thickness of the oxide film have a pronounced effect on the wettability, especially at low temperatures. To eliminate this effect, the experimental temperature must be over a critical value. Vacuum favors lowering this value compared with atmosphere, and the improved sessile-drop method, particularly using an impingement-dropping mode (I-mode), helps to weaken this effect by mechanical disruption and removal of the oxide film. However, the dropping distance and the dropping force must be controlled to prevent an overspreading of the drop. The effects of the substrate surface roughness and temperature are not significant in the case of a clean aluminum surface and a fine-prepared alumina surface. On the other hand, the effect of the alumina surface crystallographic orientation is noticeable and the wettability is in the order of R 〉 A 〉 PC 〉 C. The intrinsic contact angles of the Al/α-Al2O3 system in the temperature range of 1000°–1500°C were estimated to be 76°–85° for the R and A faces, 88°–100° for the C face, and 77°–90° for the polycrystal, depending on the temperature.
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    Acicular Mullite Crystals in Vitrified Kaolin (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The microstructure of vitrified kaolin ceramic tapes has been studied via scanning and transmission electron microscopy (SEM and TEM). The sintered samples contained crystalline phase of predominantly stoichiometric mullite (3Al2O3·2SiO2), which consisted of high aspect ratio, acicular crystals that are often referred to as secondary mullite. These crystals were interlocked and embedded in an aluminosilicate glass matrix of inhomogeneous composition. The glass matrix contained an average of ∼3.63 wt% K as determined by energy-dispersive X-ray analysis (EDS), whose composition could be approximated to 5Al2O3·16SiO2·0.1MgO·0.3K2O·0.15TiO2·0.12Fe2O3. The acicular crystals have approximately the stoichiometric composition of Al2O3:SiO2= 3:2. They have grown along a specific crystallographic orientation along the [001] axis. The crystal growth front exhibited facetting on the {110) planes with microfacetting on both the {100) and {010) planes.
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    Oxygen-Deficient Anatase Precipitated from High-Temperature Plasma (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Feeding atomized aqueous solutions containing TiCl4 into an argon high-temperature inductively coupled plasma (ICP) resulted in the formation of mixtures of white and blue particles. The mixtures consisted of anatase and an extra phase of rutile. Adding oxygen to the ICP led to the production of a single phase of white anatase. The blue particles could be characterized as oxygen-deficient anatase. Electrophoretic mobility measurements indicated that Na+ participated in determining the surface potential of the mixtures. The oxygen defects may provide the adsorption sites to Na+.
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    Density, Surface Tension, and Viscosity of PbO-B2O3-SiO2 Glass Melts (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The density, surface tension, and viscosity of the melts from the PbO-B2O3-SiO2 system have been measured at temperatures in the range 1073–1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ∼60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30–60 mol%, and mainly by the PbO content in the range of the PbO content 〉60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction.
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    Rapid Prototyping of Piezoelectric Ceramics via Selective Laser Sintering and Gelcasting (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This article presents a new lost mold rapid prototyping method which combines selective laser sintering (SLS) and gelcasting techniques for fabricating piezoelectric ceramics. SLS was used to fabricate sacrificial molds of the desired structure of the ceramic part. Then aqueous PZT (lead zirconate titanate) suspension was cast in the mold and solidified in situ through formation of a three-dimensional network gel. Because the polymer mold can be easily removed at the initial stage of sintering and the gelcast PZT body has a high green strength, the desired geometry of the PZT part can be completely retained after sintering of the ceramics. Complex-shaped PZT parts were successfully fabricated after using concentrated PZT suspension with low viscosity. Densities and electrical properties, such as the d33, the relative permittivity ε, the dielectric loss tgδ and the electromechanical coupling factor Kp of the gelcast PZT parts were also compared with those of the die-pressed PZT samples. The results indicated that the gel-forming process did not deteriorate the electrical properties of the samples, if proper dispersant was selected in developing concentrated ceramic slurry.
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    Synthesis and Sintering of Cerium(II) Monosulfide (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cerium monosulfide (CeS) powder was synthesized by the reduction of Ce2S3 powder with metallic Ce, which was obtained from ceria (CeO2) powder using carbon disulfide (CS2) gas. To obtain the maximum amount of CeS from a mixture of Ce2S3 and Ce, an excess amount of metallic Ce, a stoichiometric composition, was necessary in the synthesis at 1273 K for 10.8 ks. The preliminary sintering experiments also were performed using a synthetic CeS powder containing a small amount of Ce, Ce2O2S, and β-Ce2S3 as impurities. It was found that the oxygen content in the sintered compact decreases gradually as the sintering temperature increases, because of the removal of the impurities due to the evaporation of the volatile CeO. Single-phase CeS was formed by sintering at 2173 K. To evaluate the activation energy for densification of single-phase CeS, a CeS powder was prepared by milling an initial sintered compact and was used as an ingredient for hot-press experiments. Densification data during hot-press sintering were analyzed using a kinetic equation, showing that boundary diffusion is a rate-limiting process. The results suggest that this boundary diffusion model can explain well the densification data, with an apparent activation energy of 479 kJ·mol-1.
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    Coarsening Process of Penetration-Twinned Grains in PMN-35 mol% PT Ceramics (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In a Pb(Mg1/3Nb2/3)O3-35 mol% PbTiO3 (PMN-35PT) specimen with 5 mol% excess PbO, the pores trapped inside grains by heat treatment in a double cycle at 1150°3C have revealed the coarsening pattern of the grains. Using this technique, the coarsening process of abnormal large grains with typical characteristics of penetration twins could be determined. The results suggest that two-dimensional nucleation and lateral growth enhanced at the reentrant edges are the cause of zigzag-shaped σ3 incoherent twin boundaries.
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    Small-Angle Neutron Scattering and Rheological Characterization of Aluminosilicate Hydrogels (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Structure and formation of aluminosilicate hydrogels were investigated as a function of chemical composition. Oscillatory rheometry was used to measure the dynamic moduli, G‘ and G“, of the gels during setting. The formation of aluminosilicate hydrogels was monitored over time as a function of the storage modulus for gels of low solids volumes, φ 〈 0.030. Overall gel strength correlated well to the fractal dimension, D, observed by neutron scattering. Scattering data were interpreted using the power law, and the Guinier relationship was used to determine the size of the constructing colloidal/gel particles. Aluminosilicate hydrogels were observed to consist of large fractal aggregates of indeterminable size constructed from smaller subunits of ∼45 Å in dimension. Structure and formation of the gels were highly dependent on [Al2O3] and [Na2O] content.
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    Dense Mullite from Attrition-Milled Kyanite and Aluminum Metal (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dense mullite was produced through the reaction and sintering of an attrition-milled mixture of kyanite (Al2O3·SiO2) and aluminum metal. Kyanite and aluminum were attrition-milled then slowly heated at 1°3C/min to 1100°3C in air, and rapidly heated to 1600°3C and held for 1 h. During heating, the aluminum metal is oxidized first in the solid state and then as a liquid. The attrition-milled kyanite decomposes yielding mullite and rejecting silica, which then reacts with the alumina formed from oxidation of the aluminum. Expansion from the aluminum oxidation and kyanite decomposition partially compensates for the normal sintering shrinkage. A dense, fine-grain-size mullite results.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00144.x
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    Large Photoinduced Densification in Organically Modified Germanosilicate Glasses (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Organically modified germanosilicate (ORMOGSIL) glasses prepared by a sol-gel method showed a large refractive index change on ultraviolet exposure. The large photoinduced refractive index change in the ORMOGSIL glasses is mainly due to the structural densification caused by ultraviolet irradiation. The shifts in frequency of the Raman bands measured at room temperature reveal structural densification by reduction of the average intertetrahedral bonding angle θ in the ORMOGSIL glasses. Surface relief patterns by photoinduced densification were directly inscribed on the ORMOGSIL glasses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00155.x
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    Differential Sintering by Improper Selection of Sintering Parameters during Pulse Electric Current Sintering (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Recently, we reported on the retention of fine-grained micro-structure in Al2O3/3 vol% 3Y-ZrO2 composites using the pulse electric current sintering (PECS) technique. It was demonstrated that a high heating rate is beneficial for the retention of fine grains and homogeneous microstructure. As there are few reports on microstructural inhomogeneity and excessive grain growth in compacts densified by the PECS technique, we carried out a series of experiments on monolithic alumina by varying the sintering parameters and discussed the characteristic results. All specimens that were densified under selective sintering conditions attained high density (∼99% of the theoretical density) at 1250°3C in 〉 5 min. The average fracture strength of monolithic alumina was observed to be 741 ± 25 MPa and the fracture toughness was 2.2 MPa.m 〈1/2, and these were reasoned out to small grains. However, compacts sintered under very low compaction pressure attained ∼92%-93% of the theoretical density, and these specimens had undesirable microstructural inhomogeneity owing to differential sintering. Hence, in the present study, we address the problem of differential sintering.
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    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00159.x
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  • 77
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    CORRECTION (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 82 (1999), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.1999.tb20092.x
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  • 78
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    Edge Stresses in Alumina/Zirconia Laminates (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Using the technique of fluorescence piezospectroscopy, we determine the distribution of thermal residual stresses across the edges of three laminated alumina/zirconia composites. We develop a methodology for separating the measured stress state into microstresses that result from grain-to-grain thermal mismatch and macrostresses that result from lamination-induced thermal mismatch between individual plies. Comparison between the measured edge-stress distributions and those calculated based on a simple force-superposition model shows good agreement, indicating that the laminate system is well approximated as linear elastic. Given the experimental confirmation of significant edge stresses in multi-ply laminates, the possibility of failure initiating at composite edges must be considered in the design of surface-compressed laminate structures with the aim of mediating the detrimental effect of surface flaws.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03031.x
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  • 79
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    Effect of Shear Stress on the Atomistic Structure of a Grain Boundary in Strontium Titanate (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied the atomistic structure of a σ3 (111) grain boundary in strontium titanate by high-resolution transmission electron microscopy (HRTEM). Quantitative evaluation of HRTEM images reveals that shear stresses, which may originate from processing or external loading, have an important effect on the translation state of the two adjacent grains and on the ion positions at the grain boundary. While under low shear stress the boundary exhibits mirror symmetry with respect to the boundary plane and a comparatively large free volume, high shear stress transforms the structure to a “lock-in” configuration, which has no mirror symmetry and a smaller excess volume. These results suggest that internal or external stresses may significantly alter the charge transport properties of SrTiO3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03032.x
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  • 80
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    Dislocation Cores and Hardness Polarity of 4H-SiC (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The hardness of opposite basal faces of 4H-SiC single crystals has been measured in the temperature range 25°-1200°3C. A strong hardness anisotropy between the silicon-terminated (0001) and carbon-terminated (0001) faces of this polar crystal has been found. Transmission electron microscopy investigation of the dislocations in the plastic zone of the 1200°3C indentations shows that they lie predominantly on the basal planes parallel to the indented face, and the extra-half planes of the nonscrew dislocations originate from the indented face. It is also found that, when the (0001) Si-terminated face is indented, the dislocations are either widely dissociated, with the width of the stacking fault ribbon much larger than the equilibrium value, or else they are single leading partials, with the corresponding trailing partials absent. In this case, all the leading partials are found to have a silicon core. On the other hand, the dislocations in the plastic zone of the carbon-terminated face are in the form of dissociated dislocations, with the width of the associated stacking fault ribbons appreciably less than the equilibrium value. Moreover, the leading partials of éhese dissociated dislocations have a carbon core. The results indicate that the hardness of the polar basal faces of 4H-SiC at elevated temperatures is partly determined by the nature of the dislocation cores nucleated by the indentation process. It is argued that this is due to the influence of the core on the generation and glide of the leading partial dislocations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03033.x
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  • 81
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    Computer Simulations of Diffraction Effects due to Stacking Faults in β-SiC: I, Simulation Results (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: X-ray diffraction (XRD) patterns from nominally β-SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β-SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1-D Ising model with a Boltzmann-type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03034.x
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  • 82
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    Nanostructuring of Laser-Deposited Ti Films by Self-Limited Oxidation (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Local laser-induced oxidation of thin titanium films on glass is shown to be self-limiting due to a decrease in the absorptivity during the reaction. Taking advantage of this confinement, stable writing of transparent oxide line structures narrower than the diffraction-limited focused spot of a continuous wave Ar ion laser (500 nm) has been accomplished. The greatest optical contrast (1:10) with the highest resolution down to 165 nm was observed if the film thickness is of the order of the light absorption length in the metal.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03035.x
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  • 83
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    Mechanisms of High-Temperature Creep of Fully Stabilized Zirconia Single Crystals as a Function of the Yttria Content (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: High-temperature creep behavior of yttria fully stabilized zirconia single crystals with various yttria contents in the interval 9.4 ≤x≤ 21 mol% has been studied. The mechanical data have been collected as a function of both the temperature and the yttria concentration. The creep behavior has been explained in terms of a transition between a dislocation viscous glide and a dislocation climb controlled mechanism, making use of a generalized version of a classical model for alloys proposed by Burton. The yttria concentration dependence of the creep rate has been connected with results on cationic diffusivity, with a possible influence of impurities.
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  • 84
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    Debonding in Multilayered Composites of Zirconia and LaPO4 (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Multilayered composites consisting of LaPO4 (La-monazite) layers alternating with various ZrO2-based materials were fabricated to investigate whether LaPO4 provides a weakly bonded interface suitable for promoting toughening, as previously observed in the system LaPO4/Al2O3. The following ZrO2-based materials were assessed: Y-ZrO2, Y-ZrO2/Al2O3, Ce-ZrO2, and Ce-ZrO2/Al2O3. Debonding was observed in all cases. The composites containing Y-ZrO2 and Y-ZrO2/Al2O3 were stable, with no reactions, at temperatures up to at least 1600°3C. However, in the composites containing Ce-ZrO2, interdiffusion of Ce and La occurred, resulting in formation of a pyrochlore-like phase and, in the case of the Ce-ZrO2/Al2O3 composite, a (Ce,La)Al11O18 magnetoplumbite phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03038.x
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  • 85
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    Structure and Mechanical Properties of Copper/Niobium Multilayers (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Copper/niobium multilayers prepared by sputtering onto Si substrates with layer thicknesses ranging from 11 to 5000 Å have been characterized by transmission electron microscopy and nanoindentation. The films are strongly textured with {110} close-packed planes of the bcc Nb parallel to the {111} close-packed planes of the fcc Cu and close-packed directions tending to be parallel as well. For the 11 Å layers, the Cu is found to grow pseudomorphically on Nb in the bcc structure. It is thought that, for thicker layers, the bcc Cu loses coherency and transforms martensitically to the fcc phase, thus resulting in the observed Kurdjumov—Sachs orientation relationship. As the layer thickness, d, decreases from 5000 to 500 Å, the hardness increases as d-1/2; i.e., it follows a Hall—Petch relationship so that hardening is due to grain boundaries and interfaces. The slope is the same as in pure Cu, but there is a large intercept which is ascribed to internal stresses and a large dislocation density. As the layer thickness decreases from 100 to 11 Å, the hardness increases as (1/d) ln (0.69d), which is a line tension formulation such as would be expected for Orowan dislocation bowing between the layers. Again there is a large intercept which is ascribed to cutting through the Cu/Nb interfaces. The interfacial energy is calculated to be 0.46 J/m2.
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  • 86
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    Microstructure Evolution of ZrO2-(Fe2O3, Al2O3) Materials Synthesized with Solution Precursors (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Aqueous Zr-nitrate solutions containing appropriate amounts of Fe(NO3)3·6H2O and Al(NO3)3·6H2O were used to synthesize ZrO2-Fe2O3 compositions (up to 40 mol% Fe2O3) and one ZrO2-Al2O3-Fe2O3 composition. An amorphous phase was produced after pyrolysis, which subsequently crystallized to a single-phase Zr(Fe)O2 solid solution (or Zr(Fe,Al)O2 ss) that appeared cubic by X-ray diffraction, but tetragonal (c/a→ 1) by electron diffraction. The crystallization temperature increased with Fe2O3 content. At higher temperatures, the single phase partitioned to two phases, tetragonal-ZrO2+γ-Fe2O3. The γ- to α-Fe2O3 transformation occurred at still higher temperatures to produce a two-phase microstructure composed of two interpenetrating phases (ZrO2+α-Fe2O3), each with equiaxed grains. This microstructure was relatively stable to grain coarsening, even to temperatures just below the apparent eutectic temperature. With the exception of the lower transition temperatures and the equiaxed grains observed for both phases, these observations are similar to that previously reported for the ZrO2-Al2O3 system. The microstructure development reported here is another example for the synthesis via solution processing that involves diffusion-limited crystallization. Namely, a two-phase material can be produced where the grain size of each can be very small, and can be prevented from growing rapidly at high temperatures due to the constraint of each phase on one another.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03039.x
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  • 87
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    Ferroelasticity of t‘-Zirconia: I, High-Voltage Electron Microscopy Studies of the Microstructure in Polydomain Tetragonal Zirconia (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The microstructure of polydomain tetragonal zirconia (t-ZrO2), i.e., a ZrO2 modification exhibiting ferroelastic behavior, is studied by high-voltage electron microscopy. This material consists of three domain variants of the tetragonal phase with their c-axes nearly orthogonal to each other. Always two variants of these platelike domains are alternately arranged, forming elongated regular colonies. Hence, in both variants the common habit plane of the domains is a {110} twin plane. The colonies are of columnar shape with a longitudinal axis. They are bound by {110} planes, too, which are twin planes for the domains in the contiguous colonies. Owing to their particular structure and the helical arrangement of the adjoining colonies, the material remains coherent and pseudocubic over large macroscopic regions, although it is formed by different tetragonal domains.
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  • 88
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    A Natural Ceramic/Polymer Layered Composite (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The examination of natural materials at the microscopic and microchemical level from a materials science perspective can occasionally suggest advances in modern materials engineering. The present paper reports on such a case: an analytical study of the detailed structure and composition of sea urchin teeth.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03042.x
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  • 89
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    Ferroelasticity of t‘-Zirconia: II, In situ Straining in a High-Voltage Electron Microscope (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The ferroelastic deformation of t-ZrO2, the microstructure of which was described in detail in Part I, was investigated by in situ deformation experiments in the high-voltage electron microscope at 1150°3C. During the experiments those two domain variants with their c-axes perpendicular to the [010] tensile direction were transformed into the third one with its c-axis parallel to the tensile direction. The subsequent ‘switching’ of the domains inside the colonies proceeds much faster than the penetration of the transformation front into a neighboring colony. Therefore, the transformed region, exhibiting a unique tetragonal structure and containing residual defects, preferentially expands into the longitudinal directions of the colonies. The transformation of single domains proceeds instantaneously within the time resolution of the video tape recording.
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  • 90
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    Compression Test and Plastic Strain of α-Al2O3 Single Crystals (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Compression tests of single crystals are analyzed with respect to shear due to the friction at the loaded ends. This simple approach permits an explanation of the features associated with prism plane slip in sapphire (α-Al2O3), i.e., the shape changes of the specimens and the curvature of the glide planes.
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  • 91
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    Agglomeration during the Drying of Fine Silica Powders, Part II: The Role of Particle Solubility (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of particle solubility and the dissolution rate on agglomeration was studied by drying silica and titania particles from aqueous slurries with pH values in the range of 2–12. The agglomerate strength and strength distribution were measured by a calibrated ultrasonic force, and the strength increased as the solubility and dissolution rate increased. Two silica powders of different particle size (60 nm and 500 nm) were studied, and smaller-sized particles formed stronger agglomerates. The drying rate of the powders was varied by using spray drying and tray drying, and slower drying was shown to lead to higher agglomerate strength. The agglomerate strength of titania powder (insoluble in water) was independent of pH, whereas the agglomerate strength of silica was dependent on pH. It was concluded that the solubility and dissolution rate are important parameters that govern the strength of agglomerates.
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  • 92
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    Formation Kinetics of MoSi2 and Mo5Si3 by the Reactive Diffusive Siliciding of Molybdenum (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The formation kinetics of products formed by the reaction between dense molybdenum and vapor-supplied silicon at an activity approximating that of solid silicon under open flowing gas conditions was studied at 1200°3C. An outer MoSi2 layer overlaid the much thinner Mo5Si3 that formed on the molybdenum. Both phases obeyed parabolic growth laws over a 22 h period, having parabolic rate constants of 6.8 times 10-10 cm2/s for the MoSi2 and 1.3 times 10-13 cm2/s for the Mo5Si3 phases. These results were ∼2 orders of magnitude less than prior results, mostly obtained by another processing route. Possible explanations include enhanced growth rates from chemical contamination. Gross distortion and abnormal layer thicknesses at specimen edges and the 159% volume increase during siliciding suggest that the kinetics also are strain dependent.
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  • 93
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    Origin of the Positive Temperature Coefficient of Resistivity Anomaly in the ZnO-NiO System (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An anomalous positive temperature coefficient of resistivity (PTCR) was investigated in the ZnO-NiO system. It was found that the ZnOSS (Zn0.97Ni0.03O) and NiOSS (Ni0.6Zn0.4O) constituent phases of that system exhibit negative temperature coefficient of resistivity (NTCR) character, while their combination shows a PTCR effect with a maximum at 400°3C, which coincides with a large difference in the coefficient of linear thermal expansion between the ZnOSS and NiOSS phases at that temperature. On the basis of the brick wall model microstructure, the PTCR anomaly of this system can be explained. The magnitude of the PTCR effect is governed by the difference in resistivity of the two constituent phases at the temperature where the maximum of the PTCR anomaly occurs. The predicted temperature dependence of the resistance, R(T), of a model microstructure consisting of constituent phases with different grain sizes agrees well with the experimental R(T) of the prepared composite ceramics.
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  • 94
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    Effect of Ordering-Induced Domain Boundaries on Low-Loss Ba(Zn1/3Ta2/3)O3-BaZrO3 Perovskite Microwave Dielectrics (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Small substitutions of BaZrO3 into Ba[(Zn,Ni)1/3Ta2/3]O3 are utilized in the commercial preparation of low-loss perovskite microwave dielectrics. The structures of a series of these phases with substitution levels ranging from 1% to 5% BaZrO3 were examined using high-resolution TEM. For ≤ 2.15% BaZrO3 the solid solutions retain the ordered “1:2” structure of the Ba[(Zn,Ni)1/3Ta2/3]O3 end-member but are comprised of small ordered domains whose size decreases as the Zr content is raised. The decrease in the size of the domains parallels a decrease in the processing time required to access a low-loss state. Although for pure Ba[(Zn,Ni)1/3Ta2/3]O3 reductions in the degree of cation order produce a large increase in the dielectric loss, the Zr-substituted ceramics retain a very low loss. We believe the low losses of the 1:2 ceramics are derived from the stabilization of the ordering-induced domain boundaries via the partial segregation of the Zr cations. For substitutions between 3% and 5% BaZrO3 the size of the ordered domains continues to decrease but the system undergoes an abrupt transformation to a cubic “1:1” ordered structure with a doubled perovskite repeat. The structures of these phases have been interpreted using a “random layer” model in which one site is occupied by Ta and the other by a random distribution of Zn, Zr, and the remaining Ta cations, i.e., Ba{[Zn(2-y)/3Ta(1–2y)/3Zry]1/2[Ta1/2]}O3. Although the ordering is confined to nano-sized domains, these ceramics also exhibit low losses, again reflecting the relative stability of the domain boundaries. In this case we believe the low losses reflect the effectiveness of the random layer in stabilizing the anti-phase boundaries.
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  • 95
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    Oxidation of Single Crystals of Hafnium Carbide in a Temperature Range of 600° to 900°3C (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The isothermal oxidation of HfC single crystals with (100) orientation was carried out using an electromicrobalance at temperatures of 600° to 900°3C at an oxygen pressure of 2 to 8 kPa. Nonisothermal oxidation was performed by a simultaneous thermogravimetry—differential thermal analysis—mass spectrometry analysis. A polished cross section of the oxidized crystal was observed by backscattered electron imaging in a scanning electron microscope. Quantitative chemical analysis for Hf, O, and C and their elemental profiles in the HfC and oxide scale was carried out by wavelength dispersive X-ray microanalysis. It was found that the oxide scale consists of two regions, zones 1 and 2, both of which showed the existence of carbon. The carbon content at the middle point of zone 1 was about twice that in zone 2, which contained 7 to 14 at.% carbon. Zone 1 showed an almost compact and pore-free phase; its thickness remained constant (1 to 2 μm) after a prolonged time. The thickness of zone 2 increased linearly with time. The oxidation mechanism including interfacial reaction responsible for the deposition of carbon is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03048.x
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  • 96
    Electronic Resource
    Electronic Resource
    Feasibility of Using Cordierite Glass-Ceramics as Tile Glazes (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Basic principles of fabricating tile glazes based on cordieritic glass-ceramics are explained. Glass compositions from the MgO-Al2O3-SiO2 three-component phase diagram have been melted with and without the nucleating agent TiO2. Additionally, a sodium borosilicate glass that is commonly used in the tile glaze industry has been wet milled, together with the previous compositions, to produce a coating slip. Studies are focused on the role of the nucleating agent and glassy formulation in the crystallization of the glass-ceramic system using differential thermal analysis, X-ray diffractometry, and scanning electron microscopy. When added to a borosilicate glass, only one composition is capable of crystallizing cordierite under a fast-firing cycle used for “monoporosa” production. The porosity of the glaze layer is sufficiently low and the crystal size is small to ensure good mechanical and chemical properties. The presence of cordierite crystals in the glaze should enhance abrasion and acid resistance, in comparison to a traditional matte glaze that contains mostly enstatite or diopside crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03049.x
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  • 97
    Electronic Resource
    Electronic Resource
    Synthesis of Ba2NaNb5O15 Powders and Thin Films Using Metal Alkoxides (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Transparent and highly oriented Ba2NaNb5O15 (BNN) thin films have been prepared by using metal alkoxides. A homogeneous precursor solution was prepared by the controlled reaction of NaOC2H5, Nb(OC2H5)5, and barium metal. The BNN precursor included a molecular-level mixture of NaNb(OC2H5)6 and Ba[Nb(OC2H5)6]2 in ethanol. The alkoxy-derived powder crystallized to a low-temperature phase, and then transformed to orthorhombic BNN (tungsten bronze) at 600°3C. BNN precursor films on substrates crystallized to orthorhombic BNN at 800°3C via the low-temperature phase. Highly (002) oriented BNN films of tungsten bronze structure were successfully prepared on MgO (100) substrates at 700°3C by using BNN underlayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03050.x
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  • 98
    Electronic Resource
    Electronic Resource
    Computer Simulation of Grain Growth and Ostwald Ripening in Alumina—Zirconia Two-Phase Composites (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of grain growth and Ostwald ripening in Al2O3-ZrO2 two-phase composites was systematically investigated using two-dimensional (2-D) computer simulations, based on a diffuse-interface field model. Using average values for the experimentally measured ratios of the grain boundary energies to the interphase boundary energy as the input, the predicted 2-D microstructural features and their evolution are in excellent qualitative agreement with experimental observations on 2-D cross sections of 3-D Al2O3-ZrO2 two-phase composite microstructures. It was found that the coupled grain growth in Al2O3-ZrO2 composites is controlled by long-range diffusion and the average size (Rt) as a function of time (t) follows the power-growth law, Rmt - Rm0=kt with m= 3, which is independent of the initial microstructures and volume fractions of the two phases. The predicted variation of the kinetic coefficient (k) on the volume fraction follows a trend similar to that experimentally measured through the entire range of volume fractions. The scaling of grain size distributions is observed at a given volume fraction, i.e., they are time-invariant in the steady state. However, the characteristics of size distributions vary with the initial microstructures and the volume fractions. The relationship between matrix grain size and second-phase grain size is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03051.x
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  • 99
    Electronic Resource
    Electronic Resource
    Aqueous Processing of Sintered Reaction-Bonded Silicon Nitride: I, Dispersion Properties of Silicon Powder (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An aqueous-based system (Si-Al2O3-Y2O3-Fe2O3) for processing sintered reaction-bonded silicon nitride (SRBSN) was investigated with an emphasis on chemical control of suspension component interactions. Chemical stability and dispersion properties of a commercial silicon powder were characterized using electroacoustic, adsorption isotherm, and rheological measurements. The interactions of silicon with nitriding agent, sintering aids, dispersants, and binder were considered. The effects of pH, electrolyte, aging, particle size, and solids loading were examined. The suspension properties of the silicon powder were influenced by the native oxide film and powder treatment history. The silicon—oxide composite particles exhibit dispersion behavior similar to silica, characterized by a negative surface potential above pH 2. A method to improve the dispersion and homogeneity of suspension components based on the use of quaternary amine dispersants is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03052.x
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  • 100
    Electronic Resource
    Electronic Resource
    Minimizing Infiltration Times during Isothermal Chemical Vapor Infiltration with Methyltrichlorosilane (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Minimum infiltration times during isothermal chemical vapor infiltration were calculated for the formation of a silicon carbide matrix composite from methyltrichlorosilane (MTS). Several different reaction models were used to describe the SiC deposition kinetics. The results show that the nature of the reaction model has a significant effect on process optimization considerations. It is clear that a simple first-order deposition reaction does not accurately describe the infiltration process, while rate expressions that treat the effect of chlorine-containing byproduct gases provide much more accurate predictions. In theory, much shorter infiltration times can be obtained with precursor chemistries that do not produce Cl-containing gases. The results also provide guidelines for minimizing infiltration times with MTS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03055.x
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