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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    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 to cast functionally gradient porous ceramics was conceived and established. A previous initial study had established viability of the technique: samples were shown to have a functionally gradient cross section with a continuously increasing mean particle size from top to bottom. This article reports on a modified two-level factorial experimental design that was undertaken to determine the interdependent effects of pH, polyelectrolyte additive concentration, sintering temperature, and powder blend on the sintered microstructure. Ceramic disks ∼45 mm in diameter and 3.3 mm thick were cast by sedimentation. The green bodies were dried prior to sintering. For each point in the experimental space, mercury porosimetry was used to obtain the porosity and pore-size distribution in the solid sample. From metastable suspensions, it was possible to form functionally gradient porous structures. Porosimetric data obtained in this study corroborated previous observations. Structures were produced with a wide pore-size range and high porosity (up to 0.68). These structures, formed from a one-step process, could be used as-is for ultrafiltration applications, but they also had a sufficiently fine top layer for facilitating subsequent thin-coating operations.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The preparation of dense homogeneous zirconia-toughened alumina (ZTA) with high dry-sliding wear resistance is described. These ZTA ceramics are obtained by sintering green compacts, made by colloidal filtration of well-defined ZrO2-Al2O3 particle suspensions, for 2 h at 1400°C. The optimum solid and stabilizer concentrations for the filtration process were determined. The sintered ZTA microstructure consists of a homogeneous distribution of zirconia grains in an alumina matrix with grain sizes of 0.2 and 0.5 µm, respectively. In pin-on-disk tribological measurements at relatively high initial contact pressures (1130 MPa) and sliding speeds (0.5 m/s) a very low specific wear rate (about 5 × 10-8 mm3/(N·m)) and a coefficient of friction of 0.45–0.55 were found. It is shown that, in this case, wear is dominated by abrasion and polishing.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    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 is an attempt to identify the causes of defects that appear in large ceramic injection molded bodies after sintering. It asks the question: are such defects established at the injection molding stage or are they caused by the debinding process or by sintering? Moldings with ascending thickness were prepared using a mold cavity with replaceable tool faceplates. Control over pressure during solidification was compared by using conventional molding and a novel molding technique that uses an insulated sprue. The organic vehicle is polyoxymethylene, which can be displaced by catalytic degradation in the solid state. This is a shrinking unreacted core process with a clearly defined reaction boundary in which there is no provision for particle movement in the liquid state. This study tracks the development of defects at each stage and concludes that the defects apparent after sintering have their origin in injection molding, even though they do not mature until a later stage.
    Type of Medium: Electronic Resource
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  • 4
    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 Sr-Ta-O perovskite phase has been synthesized by a chemical preparation route and crystallized on Pt-coated SiO2/Si substrates at ∼800°C. The phase was isolated as a thin film only (not as a polycrystalline powder) and is likely metastable. SEM, EDS, XRD, EPR, and Raman analyses suggest this phase is cation-deficient, having the formula SrxTaxO3 (x∼ 0.85). X-ray Rietveld analysis indicates the structure to be a simple-cubic perovskite-type lattice; Pm3m space group, a= 3.955(2) Å, V= 61.86 Å3, Z= 1. Electrical property measurements recorded a dielectric constant k of ∼16 with a tan delta of 0.04.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    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 electrical behavior of commercial ZnO varistor devices has been examined with voltage contrast microscopy and point contact dc electrical measurements. Nonlinear voltage-dependent behavior has been observed across both of the major crystalline boundary types present in the system: Bi2O3 layer containing ZnO grain boundaries (or grain boundaries) and antimony spinel layer internal ZnO inversion twin boundaries (or twin boundaries). Twin boundaries, which bisect practically every grain in a typical commercial device, possess potential barriers with higher average breakdown voltages than do grain boundaries. Certain zinc antimonate spinel (Zn7Sb2O12) grains are electrically isolated from the matrix, whereas others are conductive within the matrix.
    Type of Medium: Electronic Resource
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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: Microwave dielectric properties of Ca1-xSm2x/3TiO3 ceramics were investigated as a function of the amount of Sm3+ substitution (0.0 ≤x≤ 0.8). The structure was changed from orthorhombic perovskite at x= 0.0 to tetragonal at x= 0.6. As the calcium vacancy concentration increased with increased Sm3+ substitution, the unloaded Q value (similar/congruent 1/tan delta) increased up to the solid-solution limit at x= 0.6 and then decreased because of formation of the secondary phase Sm2Ti2O7. The dielectric constant decreased with increased Sm3+ substitution. The effects of Sm3+ substitution on dielectric loss and dielectric constant of the specimens were analyzed by the infrared reflectivity spectra in the range 50–4000 cm−1, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The correlations among dielectric constant, dielectric loss, and dispersion parameters were studied.
    Type of Medium: Electronic Resource
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  • 7
    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 chemically modified polycarbosilane (PC) containing organofluoric groups (PCOCF) has been synthesized from PC and fluoroalkylmethyldimethoxysilane. PCOCF acts as an efficient compaction binder for SiC powders and as a coating material with excellent oxidation resistance in wet air. PCOCF-coated SiC powders also show excellent packing properties because of the organofluoric side chains, which give highly dense green compacts. PCOCF provides a high ceramic yield of 75% and highly dense SiC ceramics. Four-point bending strength increases and the scatter in strength values decreases significantly by PCOCF coating.
    Type of Medium: Electronic Resource
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  • 8
    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: Annealed glass disks were fractured in biaxial tension under a variety of conditions; crack lengths prior to branching and the sizes of the mirror and mist regions were measured. The experimental results indicated the expected correlation between fracture stress and these fracture features, except for an extrapolation to a consistent, clearly defined y-intercept. Neither environment, surface preparation, nor the rate of applied stress was a factor in the fracture stress versus branch, mirror, or mist size relationships.
    Type of Medium: Electronic Resource
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  • 9
    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: 0.5Pb(Mg1/3Nb2/3)O3-0.5PbTiO3 thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by varying the film formation procedures and heating processes. Depending on the multilayer film formation and appropriate heating process, the films were grown with a preferential orientation. The films showed a (100)-preferred orientation and large grain-size distribution when they were directly heat-treated after deposition of amorphous layers. The films showed a (111)-preferred orientation and small grain-size distribution when formed layer-by-layer or directly heating amorphous thin films with a perovskite seed layer. These results were explained by the effect of a seed layer. Saturation polarization of the (111)-preferred films was ∼35 µC/cm2, which was somewhat higher than that of the (100)-preferred film. In contrast, the dielectric constant of the (100)-preferred film was ∼1600, which was larger than that of the (111)-preferred film.
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  • 10
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    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 corrosion behavior of two thermal-spray-fused cermet coatings has been investigated using electrochemical techniques. It has been demonstrated that, without any influence of the substrate, the coatings that are based on cobalt-chromium-tungsten-boron and nickel-chromium-silicon-boron are susceptible to localized corrosion attack in seawater. Mechanisms of corrosion occur that resemble those observed on passive alloys. Galvanic effects between the components of the coating and between the coating and the substrate can have an important role in the corrosion of thermal-spray coatings. The susceptibility of both coatings have been demonstrated to be severely affected as the seawater temperature increases.
    Type of Medium: Electronic Resource
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