摘要:

The effect of rigid inclusions on the sintering of glass powder compacts has been investigated at 600°C. The densification rates show good agreement with the rule of mixtures for inclusion volume fractions of °0.1 The transient stresses generated during sintering by the presence of the inclusions were evaluated from the sintering data. Below inclusion volume fractions of °0.12, the results are in excellent agreement with Scherer's theory for viscous sintering with rigid inclusions. At higher inclusion volume fractions, interactions between the inclusion particles lead to large deviations from theoretical predictio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04916.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Environmentally assisted subcritical crack growth along glass/copper interfaces is examined in ambient‐temperature gas environments as a function of humidity. Resulting interfacial crack velocities (v), characterised in terms of the crack extension force (G) and approximate solutions for the linear elastic stress intensity factor (K), show ν‐K curve behavior typical of (bulk) ceramics. Subcritical crack growth rates are found to be initially highly sensitive to K for G) and to show evidence of a threshold stress intensity between 0.1 and 0.25 Mp a°m1/2(region I). At higher crack velocities typically between °10–5and 10–4m/s, growth rates display a plateau and tend to become K independent (region II). Although specimen‐to‐specimen scatter is large in region I, interfacial crack velocities in moist environments far exceed those in dry environments and are over 3 orders of magnitude faster (at fixed K) than reported rat's for (bulk) s

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04917.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A new technique for monitoring stresses during sintering of a ceramic composite has been developed. The stress is measured by means of the heterogeneity stresses that build up in a sandwich compact, which consists of a layer, or plane, ofSiC fibers between two layers of ceramic powder of different thicknesses. Upon sintering, this configuration produces an asymmetric stress field across the thickness of the specimen, which results in the bending of the compact, as characterized by the curvature of the fibers. In situ observations of ihe process provide information about the temperature dependence of stress initiation.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04918.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

TiO2was sintered in HCl atmospheres to enhance the effects of vapor transport. Little or no densification is observed for temperatures between 1000° and 1300°C. Particle coarsening occurs at temperatures above 1200°C. The apparent activation energy for particle growth is 114 kJ/mol. It is concluded that the primary mass‐transport mechanism is vapor transport while the particle growth rate is limited by grain‐boundary mo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04919.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Many equations have been previously proposed to describe the elastic modulus‐porosity relation of brittle solids. The equations arc not applicable to all materials over a wide range of porosity. A new equation representing elastic modulus‐porosity relation of brittle solids has been proposed. It has been shown that the proposed equation describes best the Young's modulus‐porosity data of six rare‐earth oxides over a wide range of porosity reported by previous investigators. The equation suggests that there was some kind of ordered packing in all the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04920.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A comparison of several fracture toughness determination methods based upon the use of cracks emanating from a Vickers hardness indent to the bulk techniques of double cantilever beam and single edge notch beam is made in a tough zirconia material which shows little evidence of transformation toughening based on the amount of monoclinic phase detected by XRD on ground surfaces. Results indicate that some indentation methods yield values close to those obtained by bulk methods, in contrast to results obtained on zirconia materials which show large effects of transformation toughening.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04921.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Effect of uniformity on the resistivity was investigated for SiC‐ZrB2ceramic composites. Dispersion of ZrB2particles was numerically characterized by image analysis. Spatial fluctuation of composition greatly affected the resistivity of composites. The effective medium theory was extended to treat composites with composition spatial fluctuation. The extended theory successfully explained the effect of uniformity on the resistivity of composites in relatively uniform cases. In composites of low uniformity, enhancing the uniformity increased the resistivity by breaking chains of ZrB2particle

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04922.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04923.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The high‐Tcsuperconducting oxide Yba2Cu3O7–yhas been prepared by the amorphous citrate process. A citrate‐nitrate solution was prepared at room temperature and dehydrated at around 80°C to yield a solid precursor material. The precursor was fired to high temperature to form the desired compound. The decomposition mechanism was studied with thermogravimetric analysis and X‐ray diffraction. Intermediate products were formed during the decomposition reactions. Nearly phase‐pure Yba2Cu3O7‐ypowders were obtained by firing the precursor in air to 900°Cfor2 h. Sintered samples were typically over 90% dense and exhibited good superconducti

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04924.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Raman spectra have been recorded for glasses in the binary systems CeO2‐P2O5and Pr2O3‐P2O5. The cerium phosphate glasses were prepared having different concentrations of CeO2and the praseodymium phosphate glasses with different ratios of Pr3+to Pr4+. The spectra indicate that both cerium and praseodymium enter the glass in modifying sites. We see no changes in the Raman spectra with Pr3+/Pr4+ratio. Measurements of the density and glass transition temperature are also repor

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb04925.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY