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  • Articles  (104,996)
  • American Chemical Society  (65,688)
  • Wiley  (35,400)
  • American Ceramics Society  (3,908)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (104,996)
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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 study describes the isothermal cyclic loading dilatometry (ICLD) technique to measure the viscosity of glass-based materials. We demonstrate its merit relative to constant-load techniques in minimizing the stress history effects (changes in shrinkage anisotropy and sample microstructure) that arise due to the application of an external load. A constant-load test overestimates the viscosity by an order of magnitude compared with a cyclic load test. To obtain accurate viscosity data, maximum loading rates and longer unloading periods are desirable as they reduce effects of shrinkage anisotropy on viscosity values. Representative data for a low-temperature cofired ceramic (LTCC) material are reported. Nonparametric statistical tests revealed insignificant differences between the viscosity data sets at 5% significance level and thus indicate good reproducibility of the testing methodology.
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  • 2
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Synthesis of zirconia nanoparticles by flame spray pyrolysis (FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80–95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals.
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  • 3
    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 method based on the use of four piezoelectric resonances for three sample geometries is presented that allows one to obtain all the dielectric permittivities, compliances, and piezoelectric coefficients of a piezoelectric ceramic in complex form and, therefore, all related losses. Piezoelectric losses are responsible for heat generation and hysteresis in actuators. The method is applied to a Navy type II PZT-based piezoelectric ceramic (PZT = lead zirconate titanate), for which the full set of linear electric, mechanical, and electromechanical coefficients is given in complex form. Full sets of coefficients for the available piezoceramics are required for exploiting all the possibilities of finite element analysis, both in fundamental research (mechanisms of degradation) and in development (element design). This numerical technique is necessary to explore arbitrary shapes provided by solid free-form-fabrication technologies.
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  • 4
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Low-frequency dielectric response of air- and oxygen-sintered ceramics with the composition 0.9BaTiO3–0.1La(Mg1/2Ti1/2) O3 (0.9BT–0.1LMT) has been studied in the temperature range of 12–550 K. In comparison with pure BT, in 0.9BT–0.1LMT the dielectric permittivity maximum is shifted by almost 300 K toward lower temperatures. Both real and imaginary parts of dielectric permittivity of the solid solution, in the range 12–150 K, show a strong frequency-dependent behavior, which is typical of relaxors. On the basis of the model of exponential cluster size distribution and the Cole–Cole equation, the degree of interaction between the polar clusters was estimated. It was shown that the oxygen vacancies arising during sintering at high temperatures did not affect noticeably the relaxor properties of the material. The role of heterovalent La3+/Ba2+ and Mg2+/Ti4+ substitutions in the relaxor behavior formation is discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Integrated lead zirconate titanate thin films deposited on Pt/Ti/SiO2/Si substrates using a novel triol-based route were characterized using X-ray diffraction and transmission electron microscopy. Crack-free single-layer PZT films of up to 200 nm thick were prepared by triol-based sol–gel processing onto Pt/Ti/SiO2/Si substrates. Films ∼75 nm thick exhibited a microstructure free of pores and second phase. As film thickness increased, film texture changed from {100} to {111} perovskite. Essentially, single-phase multilayer films could be prepared by the deposition and pyrolysis of several 75 nm layers, followed by a single crystallization step. The influence of heat-treatment schedule on the microstructure and orientation of the multilayer films is discussed. Comparison has been made between multilayer films prepared using the triol-based sol and an inverted mixing order/acetic acid-based sol.
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  • 6
    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: It has been shown that polydimethylsiloxane (PDMS)–CaO–SiO2–TiO2 and poly(tetramethylene oxide) (PTMO)–CaO–TiO2 hybrids form apatite on their surfaces in a simulated body fluid (SBF) and show mechanical properties similar to those of human cancellous bones. In the present study, changes, caused by soaking in SBF, were measured in the mechanical properties of PDMS–CaO–SiO2–TiO2 hybrids with different CaO and TiO2 contents and PTMO–CaO–TiO2 hybrids with different CaO contents. Significant decreases in the strength and strain at failure of the hybrids were observed for the PDMS–CaO–SiO2–TiO2 hybrids with high CaO or TiO2 contents and PTMO–CaO–TiO2 hybrids with a high CaO content after soaking in SBF for 4 w. This indicates that incorporation of a large amount of CaO component into the hybrids should result in the deterioration of the hybrids in the body environment.
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  • 7
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 stresses of laminate structures obtained by joining single layers of pure alumina (A), pure yttria-stabilized tetragonal zirconia, 3Y-TZP (Z), and an intimate mixture of alumina and zirconia (AZ) have been determined by fluorescence (in alumina) and Raman (in zirconia) piezospectroscopy. Three symmetrical stacking sequences were examined, namely, A/Z/A, A/AZ/A, and AZ/Z/AZ, with the aim of designing structures where the higher coefficient of thermal expansion (CTE) of zirconia could be used to induce compressive stress in the external layers (and ensuing tensile stress in the central layer). Two experimental sessions, 6 years apart, were conducted on the same samples, also taking care to record the spectra from the same locations; during the time elapsed between the two sessions, the samples were kept at room temperature and humidity. The stress values in alumina obtained during the more recent session were markedly different from those observed in the first session. Monoclinic zirconia (m-zirconia) was absent in all samples in the first session, whereas up to 25 vol% zirconia could be observed during the second session. m-Zirconia could only be observed in AZ layers and not in Z layers, irrespective of the position in the stacking sequence. It was concluded that 3Y-TZP underwent spontaneous tetragonal-to-monoclinic (t–m) transformation, that is, “aging,” when mixed with alumina at the grain-size level. Aging occurred only where pristine t-zirconia was subject to tensile stresses larger than ∼400 MPa.
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  • 8
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Various glass-ceramics were prepared based on the BaO–Al2O3–B2O3–SiO2 system with the addition of La2O3, ZrO2, or NiO in an attempt to develop a suitable sealant for planar solid-oxide fuel cells operating at 800°C. To estimate the applicability of these glasses as suitable sealants, their thermal and chemical stabilities as well as the crystallization behavior and bonding characteristics of their parent glasses were investigated. The thermal properties and crystallization behavior of the parent glasses were dependent on the type of additive used, and the bonding characteristics were strongly influenced by the B2O3/SiO2 value in the glass composition. Observation of microstructural change and chemical reaction at the glass-ceramic/electrolyte interface confirmed that the prepared glass-ceramics possessed long-term stability during heat treatment at the operation temperature for up to 1000 h.
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  • 9
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 increasingly wider application of lime-based materials for the conservation and restoration of historical buildings has led to a revival of interest in lime putty. One of the most well-known and highly regarded properties of lime putty is its plasticity/workability.This paper describes the results of a rheological investigation conducted on putties having identical water content but aged for different times, with the aim of providing an objective and quantitative evaluation of plasticity. Rheological measurements have demonstrated that, all other conditions being equal, shear stress increases with aging. We propose here to consider some parameters derived from Tattersall and Bingham models that can be used as a quantitative measure of plasticity directly correlated with aging.
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  • 10
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: When a BaTiO3 powder compact was sintered in air, the abnormal grain growth (AGG) was observed to occur at the surface of the specimen. The BaO evaporation from the surface and consequent formation of eutectic liquid is suggested to be the cause of AGG. When the evaporation of BaO during sintering was prevented by embedding the specimen in the same powder, no AGG was observed to occur.
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  • 11
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 zinc titanate (ZnTiO3) was synthesized at low temperatures through the combination of a sol–gel processing and a polymer binder method. ZnTiO3 powders of ∼5 nm in size were obtained by heating pastes, which were composed of a Zn-Ti methanolic solution containing acetylacetone and an organic polymer binder, at 500°C in air. Thermal decomposition behavior of the pastes was analyzed by thermogravimetry-differential thermal analysis. Crystallinity of ZnTiO3 was examined by transmission electron microscopy. The BET measurement revealed that the powders had a relatively high specific surface area of 106 m2/g.
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  • 12
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 indirect solid freeform fabrication process is used to fabricate low-loss complex geometry periodic dielectrics for use in the microwave range. Relevant processing details, such as mold fabrication, slurry rheology, curing, and binder burnout, are discussed. Woodpile electromagnetic bandgap structures exhibiting a −40 dB well were shown to be operational at frequencies 〉110 GHz. Novel designs of planar periodic dielectric resonators with Q= 965 at 33 GHz (Q= ratio of the power stored to power lost in the resonator) were realized in alumina. Metallo-dielectric filters with low-insertion loss were also created via ISFF; modeling of these structures using resistor-inductor-capacitor-equivalent circuit analysis was performed to calculate a Q of 645.
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  • 13
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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
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  • 14
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 W2C-nanoparticle-reinforced Si3N4-matrix composite was fabricated by sintering porous Si3N4 that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W2C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W2C particles resided in the grain-boundary junctions of the Si3N4, had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W2C particles in the composite, the sinterability of the Si3N4 was improved, and a W2C–Si3N4 composite with almost full density was obtained. The flexural strength of the W2C–Si3N4 composite was 1212 MPa, ∼34% higher than that of standard sintered Si3N4.
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  • 15
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 powder-blasting characteristics of a thick film prepared using a tape-casting process have been investigated. The powder-blasting process is commonly used in the manufacturing of barrier ribs of plasma display panels. The effects of binder content and baking temperature on the powder-blasting rate of the thick film have been studied. The rates observed are discussed based on the volume fraction of the pores and the degradation of binder during the baking treatment. In addition, the effect of powder-blasting resistance of thick film on the morphology of barrier ribs formed is examined.
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  • 16
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 novel and general route to synthesize various metal nitrides (AlN, CrN, and ζ-Fe2N) from metal–urea complexes is presented. These complexes, especially metal–urea chloride, have proved to be useful precursors to metal nitrides, because urea molecules construct a coordination sphere around the metal atom and form a stable structure, compared with the air-sensitive halide. Different anions in the second coordination sphere determine the reaction mechanism. The transformation from metal–urea chloride to nitride is thought to follow a nucleation–growth mechanism, while that from metal–urea nitrate is thought to follow a nitridation mechanism. We anticipate that this metal–urea complex will find applications in the fabrication of other, more complex, nitrides.
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  • 17
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 powder-blasting angle on the powder-blasting rate of a thick film prepared using a tape-casting technique were investigated. The results revealed that the etching rate was sensitive to the angle of powder blasting. The mechanism of this dependency was discussed based on brittle fracture and erosion caused by the powders blasted on the surface of the film. In addition, a new processing route for barrier ribs for plasma display panels was attempted, using the sensitive dependency of the etching characteristics on the powder-blasting angle. It was demonstrated that the ribs could be processed successfully using layers having different etching rates.
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  • 18
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 ultrafine, undoped ZrO2 powders with median primary particle sizes of 9 and 25 nm were used to prepare ceramic suspensions for thermoplastic extrusion. The organic vehicle consisted of an industrial-grade poly(ethylene-co-vinyl acetate) (EVA) or polyethylene (PE-HD) and decanoic acid as a dispersing agent. The powder volume loadings achieved were 44% and 52% by volume for the two powders, respectively. The amount of dispersant needed was calculated from a new model based on available chemisorption sites on the powder surface. Mixing and extrusion were conducted using a conventional modular plastic processing unit. Green bodies were dewaxed up to 450°C in an inert atmosphere and sintered to full density in air at 1060° and 1100°C, respectively. Analysis of the ceramic phase content and the microstructure of the bodies is presented.
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  • 19
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Pure and mixed ZnO–SiO2 particles were made by flame-spray pyrolysis of zinc acetate and hexamethyldisiloxane or SiO2 sol dispersed in methanol or water-in-oil emulsion, respectively. The product particles were characterized by nitrogen adsorption, infrared absorption, and X-ray diffraction. The evolution of solid or hollow particle formation along the flame axis was unraveled by transmission electron microscopy after collection by thermophoretic sampling. The effects of silicon precursor and solvent on product particle characteristics were evaluated. The characteristics of the product particles were controlled by the Si precursor and solvent.
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  • 20
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    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: (Bi1/2Na1/2)TiO3 (BNT) is a prominent candidate for a lead-free piezoelectric material. In this study, BNT was synthesized using the solution/sol–gel method, in which a solution of Bi2O3 and Na2CO3 was dissolved in HNO3 as starting materials. The solution then was mixed with ethylene glycol and titanium tetraisopropoxide. The obtained BNT powder was analyzed using FT-IR, DTA-TG, Raman spectroscopy, and high-temperature XRD. Results showed that BNT crystallization occurred above 600°C. TEM investigation showed that 100–200 nm BNT particles were formed by heat-treating the sol–gel-derived BNT sol at 700°C for 6 h.
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  • 21
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: B4C powder compacts were sintered using a graphite dilatometer in flowing He under constant heating rates. Densification started at 1800°C. The rate of densification increased rapidly in the range 1870°–2010°C, which was attributed to direct B4C–B4C contact between particles permitted via volatilization of B2O3 particle coatings. Limited particle coarsening, attributed to the presence or evolution of the oxide coatings, occurred in the range 1870°–1950°C. In the temperature range 2010°–2140°C, densification continued at a slower rate while particles simultaneously coarsened by evaporation–condensation of B4C. Above 2140°C, rapid densification ensued, which was interpreted to be the result of the formation of a eutectic grain boundary liquid, or activated sintering facilitated by nonstoichiometric volatilization of B4C, leaving carbon behind. Rapid heating through temperature ranges in which coarsening occurred fostered increased densities. Carbon doping (3 wt%) in the form of phenolic resin resulted in more dense sintered compacts. Carbon reacted with B2O3 to form B4C and CO gas, thereby extracting the B2O3 coatings, permitting sintering to start at ∼1350°C.
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  • 22
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    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Deagglomeration of ceramic powders is usually accomplished by immersion of powders in a surfactant-containing liquid vehicle, followed by milling. We seek alternative mechanisms to the classical milling approach by generating a chemical pressure to break up the agglomerate. This study explores the enhanced redispersion of TiO2 ceramic compacts that contain a nonionic water-soluble polymer, poly(ethylene glycol) (PEG). PEG forms a polymer solution within the agglomerated structure during redispersion. The resulting osmotic pressure gradient forces water into the porous structure and creates a tensile stress on the particle network with magnitudes as high as 0.6 MPa. Thus, the principle to achieving redispersion is to develop osmotic pressures that exceed the cohesive strength of the agglomerated structure. A critical PEG concentration of 2.0 vol% PEG 400 with respect to titania has been determined, below which redispersion is minimal.
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  • 23
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    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 wet-chemical routes have been used to synthesize Sc2O3 nanopowders from nitrate solutions employing ammonia water (AW) and ammonium hydrogen carbonate (AHC) as the precipitants. The precursors and the resultant oxides are characterized by elemental analysis, X-ray diffractometry, differential thermal analysis/thermogravimetry, high-resolution scanning electron microscopy, and Brunauer-Emmett-Teller analysis. Crystalline γ-ScOOH·nH2O (n≈ 0.5) is the only phase obtained by the AW method. This phase dehydrates to Sc2O3 at ∼400°C, yielding hard aggregated nanocrystalline Sc2O3 powders. Three types of precursors have been synthesized by the AHC method, depending on the AHC/Sc3+ molar ratio (R): amorphous basic carbonate [Sc(OH)CO3·H2O] at R≤ 3, crystalline double carbonate [(NH4)Sc(CO3)2·H2O] at R≥ 4, and a mixture of the two phases at 3 〈 R 〈 4. Among these precursors, only the basic carbonate shows spherical particle morphology, ultrafine particle size (∼50 nm), and weak agglomeration. Sc2O3 nanopowders (∼28 nm) with high surface area (∼49 m2/g) have been prepared by calcining the basic carbonate at 700°C for 2 h.
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  • 24
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    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P2O5–SiO2 glasses. Porous glasses were prepared through hydrolysis of PO(OCH3)3, Zr(OC4H9)4, and Si(OC2H5)4. Chemical bonding of the P5+ ions was characterized using 31P-NMR spectra. The phosphorous ions, occurring as PO(OH)3 in the ZrO2-free glass, were polymerized with one or two bridging oxygen ions per PO4 unit with increased ZrO2 content. The chemical stability of these glasses was increased significantly on the addition of ZrO2, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P2O5·7ZrO2·83SiO2 glass. A fuel cell was constructed using 10P2O5·5ZrO2·85SiO2 glass as the electrolyte; a power of ∼4.5 mW/cm2 was attained.
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  • 25
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    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Three hydroxyapatite powders with different surface properties were produced by wet-chemical synthesis and characterized. The electrokinetic properties of powders dispersed in water were investigated by electroacoustic spectroscopy measurements. The different surface reactivity (pHiep and ζ potential versus pH curves) was related to the interplay of dissolution and adsorption of Ca2+ ions. With a view toward the preparation of porous bodies by sponge impregnation, the behavior of powder suspensions was studied. Four deflocculants were tested, and the optimum dispersing conditions for each powder were found. Anionic polyelectrolytes resulted in the best effective dispersing agent, with different optimum amounts added to the suspensions.
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  • 26
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    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 conversion of bottom ash from fluidized-bed combustion of municipal solid waste (MSW) to zeolite, by means of alkaline hydrothermal treatment (HT), in 1M NaOH solution, is presented in this work. The transformation of the bottom ash was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, surface area (BET-N2), and scanning electron microscopy (SEM) analyses. As a result of the HT at 100°C, Na6[AlSiO4]6·4H2O, of the structural family of zeolites, together with Ca3AlFe(SiO4)(OH)8, of the structural family of hydrogarnets, began to appear; the surface area of the bottom ash increased 11 times. At 150°C, the amount of Na6[AlSiO4]6·4H2O increased and andradite, hydroxylian (Ca3Fe2(SiO4)3−x(OH)4−x), of the structural family of garnet, was formed. After 200°C of HT, Na6[AlSiO4]6·4H2O was massively formed together with aluminum tobermorite (Ca5Si5Al(OH)O17·5H2O); Ca3AlFe(SiO4)(OH)8 decreased. The surface area of the bottom ash increased 13 times. The conversion of bottom ash in zeolite is considered of great significance, opening new opportunities for stabilization and applications of this type of waste. Zeolite and also the other compounds—aluminum tobermorite, andradite, and Ca3AlFe(SiO4)(OH)8—can substitute a variety of ionic species, which allows the bottom ash to be useful for immobilizing toxic and radioactive wastes. An equivalent study was conducted in water instead of NaOH as a reference.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 equilibria in the CeO2−CoO system at temperatures above 1500°C were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 ± 5°C. The eutectic point was calculated to be at 82 ± 1.5 mol% CoO. The eutectic phases were the CeO2-rich phase (containing 〈5 mol% CoO) and the CoO-rich phase (containing ∼0.5 mol% CeO2). At 1580°C, the solubility of CoO in CeO2 was ∼3 mol%.
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  • 28
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 oxidation behavior of SiCN–ZrO2 fibers and SiCN at 1350°C are compared. The as-measured parabolic rate constants for the two materials are nearly the same (15–20 × 10−18 m2/s). However, after implementing a correction for the difference in the compositions, the rate constant is 13.2 × 10−18 m2/s for the fiber, and 29.4 × 10−18 m2/s for SiCN. The lower oxidation rate of the fiber is ascribed to the lower carbon content in the fiber material.
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  • 29
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°–1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%–30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%–50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization.
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Many elements have been used to dope titanium dioxide (TiO2) so that it absorbs light in the visible region of the solar spectrum. We have synthesized, for the first time, (S,N)-codoped rutile-TiO2 photocatalyst using a hydrothermal method and subsequent nitridation under NH3 flow. The (S,N)-codoping causes the absorption edge of TiO2 to be shifted to the longer-wavelength region and two optical absorption bandgaps in the visible-light region. (S,N)-codoping has a better photocatalytic activity than S-doping and N-doping for degradation of methylene blue solution under visible light.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Yttrium silicate (Y2SiO5) powders of high purity have been synthesized using the sol–gel method. Alkoxide precursors were used with commercial tetraethyl orthosilicate as the silica source and yttrium propoxide synthesized from YCl3. Powders calcined from the xerogel showed submicrometer crystal sizes. These powders were sintered at temperatures 〈1300°C and are suitable for coating applications such as a thermal barrier system for SiC/SiC composites.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid-phase film during sintering. The solution-reprecipitation (S-R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid-phase film of critical thickness δo, which wets the MZF grains, is formed. The solid-state sintering that takes place before the formation of the continuous liquid-phase film is essential for the final microstructure of MZF.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Nano-sized TiO2 powders were prepared by controlled hydrolysis of TiCl4 and Ti(O-i-C3H7)4 solutions and nitrided in flowing NH3 gas at 700°–1000°C to form TiN. Nano-sized TiN was densified by spark plasma sintering at 1300°–1600°C to produce TiN ceramics with a relative density of 98% at 1600°C. The microstructure of the etched ceramic surface was observed by SEM, which revealed the formation of uniformly sized 1–2 μm grains in the TiCl4-derived product and 10–20 μm in the Ti(O-i-C3H7)4-derived TiN. The electric resisitivity and Vickers micro-hardness of the TiN ceramics was also measured.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Undoped and cobalt-doped basal inversion boundaries were fabricated in ZnO bicrystals to investigate their current–voltage characteristics. High-resolution transmission electron microscopy observations and energy-dispersive X-ray spectroscopy analyses for a cobalt-doped bicrystal revealed that the boundary was highly coherent and free from intergranular phases and precipitates, but a certain amount of cobalt was present near the boundary. The cobalt-doped bicrystals exhibited nonlinear characteristics that depended on cooling rates from annealing temperature, in contrast to linear characteristics of the undoped bicrystals. It is suggested that the presence of cobalt impurities enhances the formation of acceptor-like native defects near the boundaries to generate electrostatic potential barriers.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Nano- and mesopores of bulk silica xerogels were studied by means of positron annihilation lifetime measurement as well as nitrogen physisorption. Effects of an alkaline catalyst concentration in the sol–gel process on the pore sizes and specific surface area were investigated. The pore size was estimated from the ortho-positronium lifetime. Remarkable structural changes were found around a relative alkaline concentration of 10−4 (a molar ratio of sodium hydroxide to tetramethyl ortho-silicate). Above this particular catalyst concentration, the nanopore radius decreased from 0.45 to 0.35 nm, whereas the mesopore radius increased from 1 to 8 nm. The positron annihilation lifetime technique was effective in the evaluation of the nano- and mesoscopic structural changes of silica xerogel.
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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
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sol–gel derived silica (SiO2) films doped with nickel oxide (NiO) nanocrystals were fabricated. A bifunctional ligand was used, bearing amine groups capable of coordinating the nickel ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix. Nickel oxide nanocrystals precipitated at 500°C while the film was still porous. The nanocomposite films showed a reversible change in the optical transmittance in the VIS-NIR range when exposed to carbon monoxide gas. The effects of residual porosity, testing temperature, and carbon monoxide gas concentration on optical transmittance were studied.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 oxidation of SiC at 1200°C in a slowly flowing gas mixture of either air or air + 15 vol% H2O at 10 atm (1 MPa) was studied for extended times to examine the effects of elevated water-vapor pressure on oxidation rates and microstructural development. At a water-vapor pressure of 1.5 atm (150 kPa), distinct SiO2 scale structures were observed on the SiC; thick, porous, nonprotective cristobalite scales formed above a thin, nearly dense vitreous SiO2 layer, which remained constant in thickness with time as the crystalline SiO2 continued to grow. The pore morphology of the cristobalite layer differed depending on the type of SiC on which it was grown. The crystallization and growth rates of the cristobalite layer were significantly accelerated in the presence of the high water-vapor pressure and resulted in rapid rates of SiC surface recession that were on the order of what is observed when SiO2 volatility is rate controlling at high gas-flow velocities (30 m/s). The recession process can be described by a paralinear kinetic model controlled by the conversion of dense vitreous SiO2 to porous, nonprotective SiO2.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two commercially available additive-containing silicon nitride materials were exposed in four environments which ranged in severity from dry oxygen at 1 atm pressure, and low gas velocity, to an actual turbine engine. Oxidation and volatilization kinetics were monitored at temperatures ranging from 1066° to 1400°C. The main purpose of this paper is to examine the surface oxide morphology resulting from the exposures. It was found that the material surface was enriched in rare-earth silicate phases in combustion environments when compared with the oxides formed on materials exposed in dry oxygen. However, the in situ formation of rare-earth disilicate phases offered little additional protection from the volatilization of silica observed in combustion environments. It was concluded that externally applied environmental barrier coatings are needed to protect additive-containing silicon nitride materials from volatilization reactions in combustion environments.
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  • 41
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Fatigue behavior of four ceramic-matrix composites (CMCs) was documented at 1000°C, and a fifth composite was documented at 1200°C. Additional fatigue specimens were cycled for set blocks of cycles, removed from the fatigue machine, and exposed in a cyclic corrosion tester for 24 h with a fog of deionized water and a fog of deionized water containing 0.05 wt% NaCl. BN-fiber-coated Nicalon™/SiNC and Nicalon/Al2O3 experienced a pronounced decrease in fatigue life (∼86%) with salt fog exposure. Nicalon/C experienced rapid loss of the SiC exterior seal coat and a 30% decrease in life with salt fog exposure. Nextel610/AS and Nextel720/Al2O3 demonstrated no loss in fatigue performance or retained strength with water or salt fog exposure. Changes to the constituents of Nicalon/SiNC were evaluated to determine if they influenced moisture sensitivity. BN fiber coatings, BN or BN/SiC, alternate matrix prepreg, and matrix filler type had no influence on improving moisture resistance. Direct exposure to moisture fog produced accelerated rates of degradation in the BN fiber coating and greatly decreased fatigue durability.
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    Journal of the American Ceramic Society 86 (2003), S. 0 
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    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 performed classical molecular dynamics simulations of amorphous Si–C–N materials. The dependence of the local order and of the microstructure on the chemical composition was investigated. Our simulations show that for a stoichiometric nitrogen/silicon ratio equal to or higher than 4/3, the amorphous ceramic separates into different amorphous domains, namely C-rich, SiN-rich, and SiC-rich phases. Below this ratio, the material is composed of mixed structures, homogeneously spread within the material. For a very particular composition range, we found that carbon atoms crystallize into monoatomic graphitic layers surrounding the SiN-rich domains.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Alumina specimens with various amounts of CaO and SiO2 (1:2 ratio) were prepared, and their abnormal grain growth (AGG) kinetics were investigated. A plot of the area fraction covered by abnormal grains versus log (sintering time) had a sigmoidal shape with an apparent incubation period before the onset of AGG. The overall kinetics of AGG was similar to that of a phase transformation controlled by nucleation and growth. The incubation time and the end point of AGG were strongly dependent on the amount of liquid-forming additives. Correspondingly, the final microstructure was affected by the liquid content: a large grain size and a high aspect ratio at low liquid content and a small grain size and a low aspect ratio at high liquid content.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The electronic structure and bonding of the complex ceramic crystal Y10[SiO4]6N2 is studied by a first-principles method. It is shown that this crystal is an insulator with a direct band gap of 1.3 eV. It has some unique properties related to the one-dimensional chain structure in the c-direction and the planar N-Y bonding in the x-yplane.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A sinter-forging technique was successfully applied to fabricate a silicon nitride with a lutetia (Lu2O3) additive. The sinter-forged specimen had a strongly anisotropic microstructure where rodlike silicon nitride grains preferentially aligned perpendicular to the forging direction. The specimen exhibited superior strength of ∼700 MPa at 1500°C. This strength was highest when compared with previous silicon nitrides at temperatures 〉1400°C. Such superior high-temperature strength was attributed to grain alignment as well as to the refractory grain-boundary glassy phase and the existence of glass-free grain boundaries.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A functionally graded hybridization approach has been used in the formation of polymer-ceramic composites of polymethylmethacrylate (PMMA) and hydroxyapatite (HAp). HAp was successfully reinforced by sedimentary HAp distributions on a PMMA matrix using a centrifuge to avoid stress convergence on the interface. The stress-strain curves of the functionally graded PMMA-HAp composite showed sufficient mechanical strength with reduced brittleness. Scanning electron micrographs also showed evidence of exposed HAp on the surface of the composites.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The fracture toughness of plasma-sprayed Al2O3 coatings in terms of the critical strain energy release rate GIc was measured using a tapered double cantilever beam (TDCB) approach. The fracture surfaces were examined using a scanning electron microscope (SEM). The measurement yielded the mean GIc values from 13 to 27 J/m2 for the sprayed Al2O3 coatings at different spray distances. These values agree well with those obtained by the conventional double cantilever beam approach. The dependence of the observed GIc on spray distance is consistent with that for the lamellar bonding ratio. These results suggest that the TDCB test is a reliable approach for measuring the GIc of thermal-spray coatings without the crack-length measurement.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An indirect fused deposition process was used to fabricate controlled-porosity alumina bone grafts using a computer-aided-design file created from computed tomography (CT) scans of a horse's short pastern bone. Structures with both uniform and gradient porosity were fabricated to show the effectiveness of this process for the fabrication of custom orthopedic implants. Cytotoxicity and cell proliferation studies were conducted with different cell lines to show that these bone grafts are biocompatible. Uniaxial compression tests were also conducted to understand the influence of porosity on the mechanical properties of these structures.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Si3N4/carbon fiber composites were fabricated using several types of fiber. All the composites had higher fracture toughness compared with monolithic Si3N4 ceramics. Tribological properties were investigated by a ball-on-disk method under unlubricated conditions. The composite containing fibers with a high orientation of graphite layers and high graphite content indicated a low friction coefficient. It was identified, by Raman spectroscopy, that graphite was transferred from the composite to the Si3N4 ball of the counterbody during the wear test. This transferred layer was effective for producing the low friction behavior of the composite.
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    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 loading dilatometer was successfully developed and applied for hot forging experiments, assisted by two high-resolution laser beams and providing accurate determination of radial and axial strains. The application of various uniaxial loads linearly increased both radial and axial strain rates of cylindrical specimens if compared at constant density. Microstructural evolution during hot forging was followed with high-resolution scanning electron microscopy and quantitative analysis of pore size and orientation. Uniaxial loads led to elongated pores oriented in the direction of the applied load. This anisotropic microstructure exhibited an increased densification rate perpendicular to the loading axis, if free sintering was characterized after load removal. The imprinted anisotropy faded out during free sintering.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) was evaluated as a dispersant for nanosized 3-mol%-Y2O3-stabilized tetragonal-ZrO2 polycrystal (3Y-TZP) suspensions. The adsorption of PBTCA was characterized using the decolorization method of ferric 5-nitrosalicylate complexes. Maximum adsorption of the dispersant on the 3Y-TZP powder was found to occur at pH 3.0. At pH 〉3.0, the adsorbed amount decreased with increased pH. Semiquantitative analysis using auger electron spectroscopy showed that PBTCA adsorbed irreversibly on the powder. The surface charge of the powder was evaluated by measuring the zeta-potential in dilute powder suspensions. The suspension was most effectively stabilized at high pH by the high charge induced by the adsorption of PBTCA. Rheological properties of the suspension were evaluated as a function of dispersant amount and solids loading. The optimum amount of dispersant increased with increased solids loading for solids loading 〉20 vol%. A stable suspension of 35 nm 3Y-TZP particles with a solids loading as high as 32 vol% was obtained using PBTCA as dispersant, in contrast to 28 vol% when using ammonium polyacrylate (NH4PAA). Theoretical calculations of the interaction between 3Y-TZP particles showed that the stabilization of the suspensions was attributed to a combination of the electrostatic repulsion and a steric barrier caused by the adsorbed PBTCA. Induced coupling plasma analysis showed that PBTCA could be completely burned out during sintering, which confirmed its suitability as a dispersant for 3Y-TZP.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Phase-pure brookite of high crystallinity, which was classically obtained via hydrothermal treatment, has been synthesized under ambient pressure at 70°C via reacting a mixed solution of urea and titanium (III) chloride (instead of the widely used titanium (IV) compounds). The resultant particles are monodispersed spheres (∼154 nm) composed of brookite nanocrystals (∼25 nm), which are stable in terms of phase purity and morphology up to ∼500°C, above which a direct transition to rutile occurred. The as-made powder has a high specific surface area of ∼41.2 m2/g, which rapidly decreased to ∼9.7 m2/g after transforming to rutile at 700°C. The brookite powder shows good catalytic property for the decomposition of acetaldehyde under UV radiation.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A single-phase material (HfMg)(WO4)3 with an orthorhombic structure, A2 (WO4)3-type tungstate, has been successfully prepared for the first time by the calcination of HfO2, MgO, and WO3, substituting Hf4+ and Mg2+ for A3+ cations in A2(WO4)3. The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2(WO4)3.
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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-doped α-SiAlON (MxSi12−(m+n)Alm+nOnN16–n) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of α-Si3N4, AlN, and either (i) CeO2, (ii) CeO2+ Y-α-SiAlON seed, (iii) CeO2+ Y2O3, or (iv) CeO2+ CaO. Cerium-containing CeAl(Si6–zAlz)(N10–zOz) (JEM) phase, rather than Ce-α-SiAlON phase, forms in the sample with only CeO2, whereas a single-phase α-SiAlON generates in samples with dual doping (CeO2+ Y2O3 and CeO2+ CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; α-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and α-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5d band, because the coordination of Ce3+ in JEM and α-SiAlON is nitrogen enriched.
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    Journal of the American Ceramic Society 87 (2004), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Nano-crystalline PbSnO3 was synthesized by a sol–gel route. It was an anion-deficient pyrochlore (a=b=c= 1.0677 nm) with space group Fd3m. TEM images confirmed the nano-size of particles as ∼10 nm, aggregated into larger clusters up to 1 μm. DSC-TGA investigation revealed that the PbSnO3 was unstable 〉800°C with 2.95% weight loss. The products of the reactions, Pb2SnO4 and SnO2, were identified by in situ high-temperature XRD. The complex decomposition reactions were deduced as (2 +x)PbSnO3= Pb2SnO4+ (1 +x)SnO2+xPbO (x= 0.104). The lattice parameters of PbSnO3 were determined by high-temperature XRD. The cell volume of PbSnO3 increased with increasing temperatures. The average volumetric thermal expansion of PbSnO3 was calculated as (β= 3.35 × 10−5/°C).
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: R-curve behavior of Si3N4–BN composites and monolithic Si3N4 for comparison was investigated. Si3N4–BN composites showed a slowly rising R-curve behavior in contrast with a steep R-curve of monolithic Si3N4. BN platelets in the composites seem to decrease the crack bridging effects of rod-shaped Si3N4 grains for small cracks, but enhanced the toughness for long cracks as they increased the crack bridging scale. Therefore, fracture toughness of the composites was relatively low for the small cracks, but it increased significantly to ∼8 MPa·m1/2 when the crack grew longer than 700 μm, becoming even higher than that of the monolithic Si3N4.
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    Notes: The hydrolysis of pure and sodium-substituted calcium aluminates and cement clinker phases was investigated in situ in the temperature range 25°–170°C, using the angle dispersive powder synchrotron powder X-ray diffraction technique. The final hydrolysis product in all cases was Ca3Al2(OH)12. The intermediate phase Ca4Al2O7·19H2O was formed from the pure calcium aluminates, and the intermediate phases Ca4Al2O7·xH2O, x= 11, 13, or 19, were formed from the cement clinker phases.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An evaluation of measurements of crack opening displacements (CODs) on a commercial sintered reaction-bonded silicon nitride (SRBSN) was performed. To determine the intrinsic fracture toughness of this material, a new evaluation method is presented, which takes into account not only the near tip CODs, but the CODs of the complete crack profile. The method is applied on through-thickness cracks in bend bars and contrasted to CODs of Vickers radial cracks. A crack-tip toughness of ∼1.7 MPa·m1/2 is obtained.
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    Journal of the American Ceramic Society 87 (2004), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This work presents a detailed description of urea decomposition during direct coagulation processing of alumina suspensions. We report on the chemical equilibria involved in the decomposition of urea in an aqueous environment with and without alumina particles. The model uses the logarithm of the concentrations as variables to ensure fast convergence and nonnegativity of the solutions, and is able to give a semiquantitative description of the experimentally observed development of pH and ionic strength (specific conductivity) during the decomposition of urea in a 30 vol% solid loading alumina suspension. Assuming local equilibrium, and a homogeneous distribution of the catalyst urease and the evolving educts, the results show an increasing solubility of CO2 with increasing pH. As a consequence the production of gaseous CO2 during the urea decomposition (direct coagulation casting (DCC) process), shifting the pH from 4 to 9 occurs only when a strong buffer is present at low and medium pH. This is advantageous for the preparation of defect-poor ceramic green bodies using this internal gellation reaction in the DCC process.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Stress-rupture tests were conducted in air, under vacuum, and in steam-containing environments to identify the failure modes and degradation mechanisms of a carbon-fiber-reinforced silicon carbide (C/SiC) composite at two temperatures, 600° and 1200°C. Stress-rupture lives in air and steam-containing environments (50–80% steam with argon) are similar for a stress of 69 MPa at 1200°C. Lives of specimens tested in a 20% steam/argon environment were about twice as long. For tests conducted at 600°C, composite life in 20% steam/argon was 30 times longer than life in air. Thermogravimetric analysis of the carbon fibers was conducted under conditions similar to the stress-rupture tests. The oxidation rate of the fibers in the various environments correlated with the composite stress-rupture lives. Examination of the failed specimens indicated that oxidation of the carbon fibers was the primary damage mode for specimens tested in air and steam environments at both temperatures.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The relative partial molar enthalpies, ΔH̄SiO2, of SiO2 in SiO2–M2O (M = Li, Na, K and Cs) binary and SiO2–CaO–Al2O3ternary melts were directly measured by drop-solution calorimetry at 1465 K and 1663 K. ΔH̄SiO2 changes from exothermic to endothermic as silica content increases, confirming the tendency toward immisciblity seen from activity measurements. It is concluded that ΔH̄SiO2 is negative due to acid-base reactions and charge-coupled substitutions when the melt is composed of fewer Q4 and more Q3 and Q2 species, but positive due to structural strain when the melt is composed of mostly Q4 species. The ΔH̄SiO2 obtained by calorimetry is a useful measure of basicity, when comparing different alkali and alkaline earth oxides.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The YO1.5–ZrO2 system consists of five solid solutions, one liquid solution, and one intermediate compound. A thermodynamic description of this system is developed, which allows calculation of the phase diagram and thermodynamic properties. Two different solution models are used—a neutral species model with YO1.5 and ZrO2 as the components and a charged species model with Y3+, Zr4+, O2−, and vacancies as components. For each model, regular and subregular solution parameters are derived from selected phase equilibrium and thermodynamic data. The neutral species and charged species modeling results are compared.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Anatase (TiO2)/silica (SiO2: 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO4) and sodium metasilicate (Na2SiO3) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO4 and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as-prepared TiO2/SiO2 composite nanoparticles showed far more improved photocatalytic activity than the pure anatase-type TiO2. The composite nanoparticles formed from (i) TiOSO4 and Na2SiO3 as well as those from (ii) TiOSO4 and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The machinability of a thermoplastic compound that consisted of 52 vol% ceramic particles and 48 vol% thermoplastic binders was investigated. To investigate the machining mechanisms, various blends of a ductile polymer (ethylene ethyl acrylate (EEA)) and a brittle polymer (isobutyl methacrylate (IBMA)) were used as thermoplastic binders. The fraction of IBMA to EEA in the blend was increased from 0 to 50 vol%. As the IBMA content was increased, the thermoplastic compound exhibited a stiffer stress versus strain response under compression because of the brittle nature of the IBMA polymer. The machinability of the thermoplastic compound was remarkably improved with increased IBMA content because of the mitigation of the extensive deformation of the thermoplastic compound.
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    Notes: A transparent and stable monodispersed suspension of nanocrystalline barium titanate was prepared by dispersing a piece of BaTiO3 gel into a mixed solvent of 2-methoxyethanol and acethylacetone. The results of high-resolution transmission electron microscopy (HR-TEM) and size analyzer confirmed that the BaTiO3 nanoparticles in the suspension had an average size of ∼10 nm with a narrow size distribution. Crystal structure characterization via TEM and X-ray diffraction indicated BaTiO3 nanocrystallites to be a perovskite cubic phase. BaTiO3 thin films of controlled thickness from 100 nm to several micrometers were electrophoretic deposited compactly on Pt/Ti/SiO2/Si substrates. The deposited thin film had uniform nanostructure with a very smooth surface.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A novel in situ hydrothermal method involving the slow dissolution of silicate glasses as a source material was used to successfully prepare b-axis-oriented high-silica zeolite ZSM-5 (MFI) thin films.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Highly (001)-oriented (Pb0.76Ca0.24)TiO3 (PCT) thin films were grown on Pt/Ti/SiO2/Si substrates using a sol–gel process. The PCT film with a highly (001) orientation showed well-saturated hysteresis loops at an applied field of 800 kV/cm, with remanent polarization (Pr) and coercive electric field (Ec) values of 23.6 μC/cm2 and 225 kV/cm, respectively. At 100 kHz, the dielectric constant and dielectric loss values of these films were 117 and 0.010, respectively. The leakage-current density of the PCT film was 6.15 × 10−8A/cm2 at 5 V. The pyroelectric coefficient (p) of the PCT film was measured using a dynamic technique. At room temperature, the p values and figures-of-merit (FD) of the PCT film were 185 μC/m2K and 1.79 × 10−5 Pa−0.5, respectively.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Amorphous carbon nitride with high nitrogen content (N/C = 1.14) was first successfully synthesized via a novel gas-solid reaction between carbon tetrachloride (CCl4) vapor and melamine (C3N6H6) at 600°C under atmospheric pressure. The product has been characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and simultaneous thermogravimetry-differential scanning calorimetry. It was revealed that the carbon nitride is sp3-dominated and the reaction-driven sp2 to sp3 transformation in the material was proposed. The electrical properties of the material were also investigated, showing high p-type conductivity.
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    Notes: BaTiO3-based ferroelectric glass-ceramics with the composition 0.65(Ba1−X SrX)TiO3·0.27SiO2·0.08Al2O3 (X= 0.2–0.6) were fabricated, and their tunable dielectric properties were measured at microwave frequency. Major crystalline phases that precipitated during thermal treatment up to 1000°C were (Ba,Sr)TiO3, Ba2TiSi2O8, and BaAl2Si2O8. The Curie temperatures of the heated bulk samples were successfully tuned near room temperature at the composition between X= 0.2 and 0.3. A thick-film sample with X= 0.3 showed 27% tunability at 5 GHz under 10 kV/cm bias voltage.
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    Notes: The deformation behavior of nanocrystalline monoclinic ZrO2 polycrystals (nanocrystalline MZP) was studied at 1273–1373 K in compression tests. The deformation of nanocrystalline MZP was characterized by stress exponent (n= 2.5), grain-size exponent (p= 2.5), and apparent activation energy (Q= 350 kJ/mol). The values of n and p were similar to the superplasticity of high-purity Zn-22% aluminum alloy. The strain rate of nanocrystalline MZP was faster than that of Y2O3-stabilized tetragonal ZrO2 (Y-TZP) at temperatures lower than the monoclinic-tetragonal transition temperature. The strain rate of MZP gradually approached to that of Y-TZP as the temperature increased to the transition temperature. The comparison of present data with published data suggested that trace amount of impurities affected the deformation behavior of MZP.
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    Notes: The microstructural evolution of nanocrystalline ceria produced by sol–gel has been analyzed as a function of the calcination temperature employing a novel nondestructive method based on the modeling of the whole X-ray diffraction pattern. The results have been thoroughly verified by transmission electron microscopy. A variation both in the average size and in the distribution of the crystalline domains is evidenced. In addition, information concerning lattice defects can be inferred on a larger scale than that normally accessible by microscopy techniques.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanical and setting properties of calcium phosphate cements are considerably determined by the pretreatment of the constituents. In this report we show for the first time that prolonged high-energy ball milling of α-tricalcium phosphate (α-TCP) led to mechanically induced phase transformation from the crystalline to the amorphous state. The amorphous material demonstrated a high reactivity such that the time for substantially complete conversion of α-TCP to calcium-deficient hydroxyapatite in 2.5% Na2HPO4 solution decreased from about 20 h (1 h of grinding in ethanol, 85% relative crystallinity) to 4–6 h for a material with a crystallinity of 8% (24 h of grinding). This reactivity could be attributed to an increased thermodynamic and kinetic solubility of the ground materials. Mechanically activated α-TCP cements were produced with compressive strengths of up to 80 MPa and setting times of 5–16 min. The effect of reactant preparation and cement mixing parameters on the physical and chemical properties of mechanically activated α-TCP cement was investigated. By comparing cements of similar porosity and degree of conversion it was demonstrated that apatite specific surface area has a strong influence on cement mechanical performance, which highlights the importance of this previously overlooked parameter in improving strength.
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    Notes: Reaction products formed during alkaline activation, with 8M NaOH solutions, of fly ashes have been characterized with 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. In particular, the influence of curing conditions (time and temperature of reaction) has been analyzed. NMR results show the formation of amorphous tecto-silicates in which the amount of aluminum decreases in the two consecutive formed phases. The Si/Al ratio of zeolite precursor obtained at 85°C changes from 0.95 to 1.86 when curing time is increased from 5 h to 1 week. The evolution of the mechanical properties of prepared cements has also been discussed in terms of the phases formed and texture and morphology of samples.
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    Notes: Silicon carbide (SiC) specimens were amorphized with neon ions and annealed at 1273 K via transmission electron microscopy (TEM). Two types of annealing procedures were conducted: (i) continuous annealing for 60 min and (ii) annealing for 5 min, repeated 10 times. TEM observations revealed that crystal nucleation was more apt to occur in the SiC amorphized by repeated annealing than in the continuously annealed SiC.
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    Notes: Three types of climb-dissociated partial dislocations were observed by high-resolution transmission electron microscopy in monazite (LaPO4) that was indented at room temperature. Two types were found on twin boundaries, and a third in the lattice. Formation mechanisms are discussed. Glide of climb-dissociated partial dislocations that is allowed by stacking fault migration is considered.
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    Notes: Simultaneous measurements of remote electron beam induced current (REBIC) and orientation imaging microscopy (OIM) in a scanning electron microscope (SEM) have been applied to a polycrystalline (Ba0.6Sr0.4)TiO3 with a positive temperature coefficient of resistivity (PTCR) to elucidate a grain-boundary character dependence of the potential barrier formation. The absence of electrical activity in a coherent Σ3 twin boundary is clearly imaged. The resistivity of individual grain boundaries estimated from a resistive contrast image is interpreted in terms of geometrical coherency, which is defined by the degree of coincidence in the reciprocal lattice points.
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    Notes: A visible-light active TiO2−xSx in rutile structure has been synthesized by means of a mechanochemical method. The method is composed of two steps: the first is grinding the mixture of sulfur and TiO2, and the second is calcining the ground sample at 673 K in an inert gas flow. XPS analysis confirms that sulfur has been successfully doped into TiO2. The calcined sample under irradiation of visible light with wave-length over 510 nm has shown good performance for NO gas destruction, suggesting its high photograph-reactivity.
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    Notes: Submicrometer TiC/SiC composites were fabricated by a rapid reactive sintering process through spark plasma sintering (SPS) technique using the carbon, titanium, and nanosized-SiC powders without any additive. It was found that the composite could be sintered in a relatively short time (8 min at 1480°C) to 97.9% of theoretical density. After sintering, the phase constituents and microstructures of the samples were analyzed by X-ray diffraction techniques and observed by scanning electron microscopy. The effect of nanosized and microsized SiC additives on the microstructure of TiC/SiC composites was investigated.
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    Notes: The microstructural evolution of nanocrystalline anatase TiO2 during high-energy planetary ball milling was studied. The results show that mechanical activation induces the transformations of nanocrystalline TiO2 from anatase to srilankite and rutile at room temperature and under ambient pressure. As the milling time increases, more anatase powder transforms to the srilankite and rutile phase, and the particle size of the powder decreases. There is no indication of the formation of amorphous phase during ball milling.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Zirconium diboride (ZrB2) and ZrB2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing. Four-point bend strength, fracture toughness, elastic modulus, and hardness were measured. Modulus and hardness did not vary significantly with SiC content. In contrast, strength and toughness increased as SiC content increased. Strength increased from 565 MPa for ZrB2 to 〉1000 MPa for samples containing 20 or 30 vol% SiC. The increase in strength was attributed to a decrease in grain size and the presence of WC.
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  • 82
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Surface modification by ion implantation has been conducted to improve the tribological properties of a high-strength and high-fracture-toughness unidirectionally aligned silicon nitride (UA-SN). B+, N+, Si+, and Ti+ ions were implanted into the planes parallel and normal to the grain alignment of the UA-SN with a fluence of 2 × 1017 ions/cm2 at an energy of 200 keV. The ion implanted UA-SN showed a dramatic improvement in wear resistance. For example, the specific wear rate of the Si+-implanted specimen in the direction parallel to the grain alignment was reduced to a value of 3 × 10−10 mm2/N, equal to 1/20 of the unimplanted one. Cross-sectional transmission electron microscopy indicates the high wear resistance was attributed to the amorphous surface caused by the ion implantation.
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  • 83
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Formation of an amorphous Al2Si2O5 layer on a steel pipe surface, after granite–dry steam interaction in the presence of copper, has been determined by XRD analysis and SEM (with energy dispersive X-ray microanalysis). Kinetic data indicate high-protective properties of the Al2Si2O5 layer, which formed a three-dimension substrate ∼5 μm thick, after 100 h exposure.
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  • 84
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Photosensitive hybrid titania films have been prepared from titanium butoxide modified with β-diketone and methacrylic acid. When this film is exposed to UV light, the β-diketonato chelate from the alkoxide and β-diketone is dissociated, and the unsaturated hydrocarbon of methacrylic acid is polymerized. These structural changes in the gel film have led to a difference between the solubility of irradiated and unirradiated parts in the film; therefore, a fine patternable hybrid titania film has been fabricated.
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  • 85
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Zinc vaporization of Mn-Zn ferrites was quantitatively characterized in terms of oxygen partial pressure PO2, temperature, grain size and sample geometry. The amount of zinc loss was measured as a function of time at various temperatures by a thermogravimetric method. The weight loss due to irreversible zinc vaporization showed a linear behavior with time and increased exponentially with temperature. The observed weight loss due to zinc evaporation at 1100°C was small, whereas a significant weight change was detected at 1200°C. The weight loss was even greater in a reducing atmosphere (PO2= 5 × 10−5). Below 1300°C, the diffusion of elemental zinc was sufficiently fast to compensate the zinc loss at the interface region, resulting in a linear dependence on time. At temperatures ≥1400°C, the weight change no longer followed the linear dependence and showed a rather parabolic behavior with a concave upward slope. The core shape and the gas flow around ferrite cores were important factors that affected the rate of zinc vaporization, but not the grain size.
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  • 86
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: “Reactive-templated grain growth” (RTGG) processing of Bi1/2Na1/2TiO3 (BNT)-based ceramics is reported. Molten salt synthesis was used to prepare platelike (∼0.2 μm × 5 μm × 5 μm) Ruddlesden–Popper (Sr3Ti2O7 (ST)) and Aurivillius (BaBi2Nb2O9 (BBN)) phases which were used as “templates” in studies of RTGG with BNT-based matrixes. A “citrate-gel” route was designed to produce intimately mixed, fine-grain matrixes for these studies. The analytical techniques used were powder X-ray diffraction and microstructural examination of dry-pressed and fired compacts. For mixtures templated with BBN, single-phase perovskite readily formed, and an initially heterogeneous microstructure evolved toward a dense assemblage of anisometric, micrometer-scale grains. Perovskite formation was more sluggish in the mixtures templated with ST, and the final sintered microstructure featured larger, porous grains in an equiaxed, micrometer-scale matrix. A qualitative model, which examined the excess constituents in the matrix after formation of stoichiometric ABO3 perovskite, is proposed to explain the observations. The model predicted an excess of Na2O and TiO2 in the matrix in the case of BBN templates and only excess TiO2 in the case of ST templates. The results indicate that careful examination of matrix and template chemistry could be important in the selection of systems for RTGG processing.
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  • 87
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: 0.6Pb(Ni1/2W1/2)O3·0.4PbTiO3(0.6PNW·0.4PT) of complex perovskite structure is successfully synthesized by mechanical activation of mixed oxide composition, followed by sintering at 950°C. It exhibits a considerably stable temperature dependence of dielectric constant over the wide temperature range of −120° to 20°C, although there occurs a dielectric peak at around 74°C. Raman spectroscopic studies show the coexistence of tetragonal and pseudocubic perovskite phases on sintering at 950°C, which are attributed to the inhomogeneous distribution of PbTiO3 arising from mechanical activation. The dielectric behavior can be fine tuned by thermal annealing at 750°C, leading to phase redistribution in PNW-PT.
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  • 88
    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: Nuclear magnetic resonance (NMR) relaxation time mapping in partially dried mortar is presented. Relaxation times in concrete are typically multi-exponential, and exhibit highly effective relaxation mechanisms (T1L∼ 3 ms, Δν1/2∼ 2500 Hz). One-dimensional mapping of the spin–lattice relaxation time is used to study relative changes in the water-occupied surface-to-volume ratio, as a function of mixture conditions, initial hydration period, and drying time. These results provide evidence for a penetrating microcracking phenomenon, due to local drying-induced tensile stresses. This conclusion was further supported by a relaxation time study of samples which were preconditioned so as to be at equilibrium with various relative humidities.
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  • 89
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Hydrolysis and polycondensation of poly(dimethylsiloxane) (PDMS), tetraethoxysilane (TEOS), and calcium nitrate, added with tetraisopropyltitanate (TiPT) at a TiPT/(TiPT + TEOS) molar ratio of 0.15, gave a pore- and crack-free transparent monolithic organic-inorganic hybrid material. It was speculated to be composed of a Si–O–Ti–O− network modified with methyl groups, and a Ca2+ ion ionically bonded to the network. The hybrid obtained showed a high apatite-forming ability on its surface in a simulated body fluid that is indicative of high bioactivity, as well as mechanical properties such as bending strength, Young's modulus, and strain at failure, analogous to those of the human cancellous bone. This hybrid material is expected to be useful as a new type of bioactive bone-repairing material.
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  • 90
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Crack-velocity (v–K) curves and crack-resistance (R) curves for unpoled ferroelectric and ferroelastic lead zirconate titanate (PZT) were determined for long cracks in compact-tension (CT) geometry using an in situ fracture device on the stage of an optical microscope. The steady-state crack length and the plateau value of R-curves measured at controlled constant velocities increased with increased velocity. The plateau value for 10−6 m/s was 1.2 MPa·m1/2 after 1.3 mm of crack extension and for 10−4 m/s was 1.4 MPa·m1/2 after 2.2 mm.
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  • 91
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 influence of crystal volume fraction on machining behavior was investigated for modified mica–glass-ceramic materials that contained B2O3, Na2O, Li2O, and ZnO and had low melting temperatures. The machining behavior was characterized by drilling rate under a constant drilling force and chip morphology in a cutting test. To achieve the greatest drilling rate, an optimization volume fraction of crystalline mica (40%) had to be used; a further increase in the fraction of crystalline mica resulted in a corresponding decrease in the drilling rate. For this type of mica–glass-ceramic, a continuous band of chips and a highly smooth cut surface could be formed during the cutting test at a high cutting velocity of 60 m/min and a depth of 1 mm. The results demonstrated that an outstanding machining behavior for glass-ceramics can be achieved and that it can be comparable with metallic materials.
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  • 92
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 nitride (AlN) nanopowder was successfully synthesized from transition alumina nanopowder using an NH3–C3H8 gas mixture as a reduction–nitridation agent. Phase-pure, nanocrystalline AlN powder with a specific surface area of 36.4 m2/g and a mean particle size of 51 nm was prepared under typical reaction conditions. The resulting AlN nanopowders possessed excellent sinterability, allowing full densification in conventional processing, even without the addition of sintering aids.
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  • 93
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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 nucleation sites of calcium phosphate crystals during collagen mineralization were studied by Fourier transform infrared spectrometry and transmission electron microscopy. It was found for the first time that there is another nucleation site, i.e., carbonyl (〉C=O) on collagen, besides the previous reported nucleation site of carboxyl (–COOH). By comparing the IR spectra of collagen not only with collagen/calcium phosphate but also with collagen/Ca2+, it was observed that the peak intensities of amides I, II, and III of collagen decreased significantly after mineralization. The decrease of the amide I peak intensity was mainly due to blockage of the C=O stretch. Furthermore, the peak for amide I gradually shifted to a lower wavenumber during collagen mineralization. This shift indicated that chemical interaction between carboxyl groups and Ca2+ ions formed in the mineralization.
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  • 94
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 identified the high microwave susceptibility of the sodium di-hydrogen phosphate monohydrate (NHPM), NH2PO4·H2O. This acid phosphate of sodium can be heated to 〉900°C when exposed to 2.45 GHz microwave radiation. Using NHPM and microwave energy, a novel single-step synthesis of many important crystalline NZP compounds has been accomplished in a very short time. Interestingly, the combination of microwaves and nonstoichiometric oxide precursors for the preparation of NZP materials is found to reduce the reaction temperatures and enhance the reaction kinetics further. The microwave synthesis method is found to be simple and fast, minimizing the loss of volatile chemical species from the reaction. A microwave-assisted procedure for the rapid sintering of NZP compounds has also been demonstrated. Densification (〉97%) has been achieved in 〈30 min at sintering temperature much lower than normally required in conventional processes. Finer microstructure and better densification are the main advantages of the microwave sintering in this study.
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  • 95
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Pb(Zn1/3Nb2/3)0.20(Zr0.50Ti0.50)0.80O3 ceramics of pure perovskite structure were prepared by the two-stage method with the addition of 0–3.0 wt% MnO2 and their piezoelectric properties were investigated systematically. The MnO2 addition influences in a pronounced way both the crystal structure and the microstructure of the materials. The materials are transformed from the tetragonal to the rhombohedral structure, and the grain size is enhanced when manganese cations are added. The distortion of crystal structure for samples with MnO2 addition can be explained by the Jahn–Teller effect. The values of electromechanical coupling factor (kp) and dielectric loss (tan δ) are optimized for 0.5-wt%-MnO2-doped samples (kp= 0.60, tan δ= 0.2%) and the mechanical quality factor (Qm) is maximized for 1.0-wt%-MnO2-doped samples (Qm= 1041), which suggests that oxygen vacancies formed by substituting Mn3+ and Mn2+ ions for B-site ions (e.g., Ti4+ and Zr4+ ions) in the perovskite structure partially inhibited polarization reversal in the ferroelectrics. The ceramics with 0.50–1.0 wt% MnO2 addition show great promise as practical materials for piezoelectric applications.
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  • 96
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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–property relationships were investigated to reveal the generic influence of various substituents on ferroelectric BaTiO3. Compositional modifications of ferroelectric BaTiO3 were systematically investigated for La3+ and Nb5+ substituents. A generic influence of charged point defects in breaking down the ferroelectric domains into polar clusters was demonstrated. In both types of modified BaTiO3, relaxor ferroelectric behavior was induced for higher concentrations of substituents.
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  • 97
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 dopants and processing conditions on the dielectric properties of base-metal-electroded materials was investigated. BaTiO3 materials simultaneously doped with MgO and Y2O3 additives can achieve small capacitance variation (ΔC/C), which meets the X7R specification, when the proportion of additives is abundant enough and the materials are not over-fired. Presumably, small ΔC/C values of thus obtained materials are the result of the formation of core–shell structure, which requires stringent control of material processing conditions. In contrast, X7R-type materials can be obtained in a much wider processing window, when prepared by mixing two BaTiO3 materials of suitable dielectric constant–temperature (K–T) characteristics. Duplexed materials prepared from these two end-point BaTiO3 materials with ratios ranging from 3:1 to 1:2 exhibit K–T behavior within the X7R specification, provided that one of the components possesses flat K–T behavior. Moreover, the dielectric properties of these materials were simulated using a simplified microstructural model. Simulation results indicate that the effective dielectric constant of core–shell materials, (Ke)CS, varies significantly not only with the dielectric properties of cores and shells, but also with the shell-to-core thickness ratio, whereas the effective dielectric constant of duplexed materials, (Ke)D, can be maintained at a very small ΔC/C value for a wide range of end-point constituent ratios, which agrees very well with the measured K–T properties for the materials.
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  • 98
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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: (Na1/2La1/2)(Mg1/3Nb2/3)O3 undergoes a series of phase transitions that involve cation order on the A- and B-sites of the parent perovskite structure. At high temperatures both sites contain a random distribution of cations; below 1275°C a 〈111〉 layering of Mg and Nb leads to the formation of a 1:2 ordered structure with a monoclinic supercell. A second transition was observed at 925°C, where the Na and La cations order onto alternate A-site positions along the 〈001〉 direction of the parent subcell. By quenching samples from above 1275°C to preserve the disorder on the B-site, a fourth variant of this compound was obtained by inducing A-site order through a subsequent anneal at 900°C. Although the changes in structure do not produce significant alterations in the relative permittivity (ɛr∼ 35), they do have a significant effect on the value of the temperature coefficient of the capacitance.
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  • 99
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    Journal of the American Ceramic Society 87 (2004), S. 0 
    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 BiVO4 additive was found effective for low-temperature firing of ZnNb2O6 polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO4-doped ZnNb2O6 samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q·f= 55000 GHz, ɛr= 26, and τf=−57 ppm/°C. With increasing BiVO4 addition up to 20 mol% relative to ZnNb2O6, while the quality factor Q·f was gradually decreased, the relative dielectric constant, ɛr, was linearly increased and the temperature coefficient of resonant frequency, τf, was slightly increased. The variations in Q·f and ɛr are surely attributable to the residual BiVO4 in the ZnNb2O6 matrix. An unexpected slight increase in τf is probably due to the formation of the Bi(V,Nb)O4-type solid solution.
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  • 100
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    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Symmetrical Σ7 tilt grain boundaries of alumina (Al2O3) were studied using bicrystals. Three types of Σ7 boundaries were successfully fabricated, that is, rhombohedral twin (Σ7{1[Onemacr]02}) and two types of [0001] symmetrical tilt grain boundaries with grain-boundary planes {4[Fivemacr]10} and {2[Threemacr]10} (Σ7{4[Fivemacr]10} and Σ7{2[Threemacr]10}). Their atomic structures and grain-boundary energies were investigated using high-resolution transmission electron microscopy (HRTEM) and a thermal grooving technique, respectively. HRTEM observations showed that the Σ7{1[Onemacr]02} boundary had a completely symmetrical atomic arrangement with respect to the grain-boundary plane. In contrast, Σ7{2[Threemacr]10} and Σ7{4[Fivemacr]10} boundaries exhibited asymmetrical atomic structures, which were confirmed by analyzing the atomic configurations using static lattice calculations. Thermal grooving experiments showed that the grain-boundary energies strongly depended on the properties of the grain-boundary planes.
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