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  • Articles: DFG German National Licenses  (170)
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  • 1
    Electronic Resource
    Electronic Resource
    Atomic Structure of a 36.8 (210) Tilt Grain Boundary in TiO2 (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An understanding of the atomic structure at internal interfaces is of crucial importance for the electronic and structural properties of most advanced materials. Here, we present a detailed study of the atomic structure at a [001] tilt grain boundary of σ5(210) in Tio2 (rutile). Z-contrast imaging is used to obtain a 2-D atomic map of the cation positions at the interface. Details of the charge state of cations and atomic structure around anion sites are then provided using electron energy loss spectroscopy. In particular, the spectroscopic data for oxygen is interpreted using multiple scattering theory to give 3-D structural information. These combined techniques allow a unique grain boundary structure to be defined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02857.x
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  • 2
    Electronic Resource
    Electronic Resource
    Pulse Electric Current Sintering of Al2O3/3 vol% ZrO2 with Constrained Grains and High Strength (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The pulse electric current sintering technique (PECS) was demonstrated to be effective in rapid densification of fine-grained Al2O3/3Y-ZrO2 using available commercial powders. The composites attained full densification (〉99% of TD) at 1450°C in less than 5 min. The composites sintered at a high heating rate had a fine microstructure. The incorporation of 3 vol% 3Y-ZrO2 substantially increased the average fracture strength and the toughness of alumina to as high as 827 MPa and 6.1 MPa·m1/2, respectively. A variation in the heating rate during the PECS process influenced grain size, microstructure, and strength, though there was little or no variation in the fracture toughness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00548.x
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation of YBCO Films on CeO2-Buffered (001) YSZ Substrates by a Non-Fluorine MOD Method (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: YBa2Cu3O7−δ (YBCO) films were fabricated via a fluorine-free metal organic deposition (MOD) method followed by high-temperature, low oxygen partial pressure annealing. Trimethyl acetate salts of copper, yttrium, and barium hydroxide were used as the precursors, which were dissolved in proponic acid- and amine-based solvents. After spin-coating and burnout, samples were annealed at 740°C in 180 ppm oxygen partial pressure and exposed to humid atmosphere for different times. A critical transition temperature, Tc(R=0) of 90.2 K and a transport critical current density (Jc) of 0.55 MA/cm2 (77 K and self-field) were obtained for 0.2 μm YBCO films on CeO2-buffered yttria-stabilized zirconia (YSZ) substrates. X-ray studies shows that the YBCO films have sharp in-plane and out-of-plane texture for all samples; however, the porosity of the YBCO film varies with the time of exposure to the humid atmosphere. A reaction between YBCO and CeO2 during the high-temperature anneals and formation of the reaction product BaCeO3 was confirmed by X-ray diffraction (XRD) studies. The XRD and transmission electron microscopy analysis indicated that the epitaxial relations in the film were YBCO (00l)//CeO2 (00l)//YSZ (00l) and YBCO [100]//CeO2 [110]//YSZ [110].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01669.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Delamination on the Transverse Thermal Conductivity of a SiC-Fiber-Reinforced SiC-Matrix Composite (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of delamination on the transverse thermal conductivity of a biaxial multiweave SiC-fiber-reinforced chemical-vapor-infiltrated-matrix composite was studied. The delamination process, induced by compressive loading, consisted of enlarging and widening pre-existing interply cavities in the as-received composite. Ultrasonic scanning suggested that the delamination process resulted in mechanical debonding between the plies. At room temperature, the delamination reduced the transverse thermal conductivity by a factor of ∼5. As a result of gaseous conduction in the interply cavities and/or delamination, the thermal conductivity was higher in air/nitrogen at atmospheric pressure than under vacuum, a difference that was especially pronounced in the delaminated sample. The thermal conductivity of the as-received and delaminated samples exhibited a negative and positive temperature dependence, respectively, which resulted in almost-equal values at temperatures 〉1000°C. Data analysis showed that the thermal conductivity of the delaminated composite was almost independent of the thermal conductivity of the plies themselves; instead, the thermal conductivity of the composite was controlled primarily by conduction across the delaminations at areas of direct contact, conduction through the gaseous phase within the delaminations, and radiation across the delaminations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02520.x
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  • 5
    Electronic Resource
    Electronic Resource
    Crack-Tip Toughness Measurements on a Sintered Reaction-Bonded Si3N4 (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01502.x
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  • 6
    Electronic Resource
    Electronic Resource
    Detection of Drying-Induced Microcracking in Cementitious Materials with Space-Resolved 1H Nuclear Magnetic Resonance Relaxometry (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03378.x
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  • 7
    Electronic Resource
    Electronic Resource
    Dislocation Structures of Low-Angle and Near-Σ3 Grain Boundaries in Alumina Bicrystals (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Alumina bicrystals with low-angle and near-Σ3 〈0001〉 tilt grain boundaries were fabricated using diffusion bonding to study the dislocation structures in alumina grain boundaries. The resulting grain-boundary structures were investigated using high-resolution transmission electron microscopy, and the grain-boundary energies were analyzed using theoretical calculations. It was found that partial dislocations with Burgers vectors of the type return ⅓〈10[Onemacr]0〉 were periodically located in the boundaries and that a stacking fault between pairs of partials was formed in such boundaries. The length of the stacking fault decreased with increased misorientation angles, which was reasonably predicted by the theoretical calculation. In the case of a near-Σ3 grain boundary, an array of displacement shift complete dislocations with the Burgers vector of return ⅓〈1[Onemacr]00〉 was periodically formed along the boundaries. These boundaries did not have stacking faults. The spacing between the dislocations decreased with increased deviation angle from the exact-Σ3 boundary with the tilt angle of 60°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03346.x
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  • 8
    Electronic Resource
    Electronic Resource
    Incorporation of Uranium in Zirconolite (CaZrTi2O7) (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Up to 0.15 formula unit (f.u.) of U4+ incorporated in the Zr site of zirconolite by firing CaUxZr(1−x)Ti2O7 compositions in argon at 1400°C allows retention of the 2M polytype. Further U4+ substitution for Zr, up to 0.4 f.u., produces the 4M polytype (containing ∼0.4 f.u. of U) plus the 2M polytype containing 0.15 f.u. of U. The pyrochlore structure (containing 0.6 f.u. of U) forms in conjunction with the 4M polytype at U contents of 0.4 f.u. up to 0.7 f.u. Higher U contents give the pyrochlore structure, but the solid-state reactivity of even alkoxide-based preparations becomes increasingly poor for x 〉 ∼0.7 and hot pressing in graphite dies at ∼1250°C is necessary to achieve near single-phase pyrochlore structures for x= 1. When samples of CaUxZr1−xTi2O7 stoichiometry (x= 0.1 and 0.2) are oxidized at 1400°C in air, diffuse reflectance spectroscopy (DRS) shows evidence for U5+ formation at the expense of U4+ via enhanced absorption bands, ∼50 nm in half-width, near 970 and 1500 nm and correspondingly weakened absorption at 1150 and 1660 nm. Weight gains consistent with complete oxidation of U4+ to U5+ are observed when finely powdered argon-fired samples with x= 0.1 and 0.4 are heated in air to 1200°C. Evidence for U valence states higher than +4 in both argon- and air-heated materials containing charge compensators to encourage U5+ or U6+ formation was also derived from DRS (showing U5+ in particular), and XANES. DRS shows weak absorption bands attributable to U4+ in zirconolites containing ∼0.2 f.u. of U incorporated in the Ca site via Mg or Al substitutions in the Ti sites, with the spectrum being closely but not exactly similar to that attributed to U4+ in the Zr site. Zirconolite and pyrochlore compositions which are melted at 1500° or 1550°C in argon and furnace-cooled yield broadly similar phase assemblages to the corresponding sintered materials, but there is evidence of incongruent melting in all materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00364.x
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Lateral Cracks on Fracture Toughness Determined by the Surface-Crack-in-Flexure Method (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The surface-crack-in-flexure (SCF) method uses a Knoop indenter to create small, semielliptical surface precracks in beam specimens. Lateral cracks may interfere with the primary median crack and cause errors of up to 10% in determination of fracture toughness, particularly for materials for which the fracture toughness is ∼3 MPa·m1/2 or less. Although the residual-stress-damage zone is ground or polished away by hand by removing 4.5–5 times the indentation depth, this amount may not be sufficient to completely remove the lateral cracks in low-fracture-toughness materials. A series of tests were conducted on sintered alpha silicon carbide with different amounts of material removed after indentation. Once the lateral cracks were fully removed, the SCF results concurred with single-edged-precracked-beam and chevron-notched-beam data collected in accordance with ASTM Designation C1421. A simple remedy for the SCF method is to examine the outer ground surface for remnants of lateral cracks before fracture and to remove more material if necessary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00186.x
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetics of Slag Hydration in the Presence of Calcium Hydroxide (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The reaction between ground granulated blast furnace slag (GGBFS) having an empirical formula of C7.88S7.39M3A and calcium hydroxide (CH) was investigated. The kinetics of the reaction were explored. Thermogravimetric analysis was used to monitor the consumption of CH from which rate constants were determined. Based on Knudsen's kinetic model, activation energies of 14.5, 17.9, and 22.6 kJ/mol were determined for three different mass ratios of slag and CH reacted over a temperature range of 15° to 50°C and hydrated for a period of time from 0 to 32 days. A comparison of the kinetics of the slag/CH reaction was made with slag/portland cement hydration. The basic features of both appear similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00445.x
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