摘要:

The effect of solids loading, particle‐size distribution, and suspension viscosity on the resultant microstructure of slipcast monolithic ceramics prepared from aqueous suspensions of alumina and silicon carbide was studied. Unimodal alumina suspensions (average particle size = 0.6 μm) were prepared at 35, 37, and 42 vol%. Silicon carbide suspensions (average particle size = 0.7 μm) were produced with different quantities of dispersant at 37 vol%. Similarly, aqueous alumina suspensions of 42 and 50 vol% were produced with a bimodal particle‐size distribution. The slip‐cast microstructures were characterized by mercury porosimetry and small‐angle neutron scattering, which provided pore size (distribution), pore fraction, and pore morphology. Essentially, the combination of these techniques deciphered packing differences obtained in the cake microstructures. For the alumina cakes produced from the 35,37, and 42 vol% suspensions, the individual characterization techniques, mercury intrusion, and the neutron scattering measurements showed that the cake microstructures were similar in pore size and quantity. However, comparison of the techniques and their assumptions showed differences in the pore shape. Mercury porosimetry and neutron scattering showed bimodal porosity for the cake produced from a mixture of 85% 6‐μm particles and 15% 0.6‐μm particles. Pore volume fraction and pore size increases were correlated with increased viscosity in the silicon carbide suspensions. In addition, the silicon carbide cake microstructures were measured, and homogeneity was evaluated as a function of posit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09010.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

First‐principles molecular‐orbital calculations using the discrete‐variational Xα method have been made on model clusters of α‐Si3N4and its solid solutions with lanthanide elements, which occupy interstitial sites in the structure. The formula is LnχSi12–4.5χAl4.5χO1.5χN16–1.5χ (Ln = La, Nd, Gd, Dy, Ho, Er, Tm, Yb), i.e., a Ln‐α‐SiAION solid solution. Covalent bond strength between Si and N, evaluated by overlap population, increases because of the presence of trivalent charges at the interstitial sites. When a Ln3+ion is present, antibondings occur between Ln orbitals and N/Si orbitals, and they depend significantly on the ionic radius of Ln3+. The total overlap population for the whole cluster is determined by the balance of Si‐N bond reinforcement and Ln‐N/Si antibonding. Although no lattice relaxation around the Ln3+ion is included in the present calculation, good correlation between maximum solubility and the total overlap population for the whole cluster is demo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09011.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Anatase‐TiO2cylindrical pellets were microwave sintered and partially transformed to rutile‐TiO2.The rutile concentration profile was determined as a function of location within the pellet. The rutile distribution in the microwavesintered pellets was different from that in pellets sintered by conventional fast firing. Temperature profiles within the pellets were estimated using the irreversible nature of the anatase‐rutile transformation. The estimated temperature profile within each pellet was not uniform. In the axial direction, maximum temperature occurred in the middle of the pellet. In the radial direction, maximum temperature occurred at 1 mm below the surface of the cylinder wall. Analysis of the temperature profile indicated that, although heat flow occurred in the microwave‐sintered pellet, the temperature profile did not change during a microwave exposure of 5

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09012.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Depending on the calcium:phosphorus molar ratio of the initial precipitates determined by precipitation conditions (calcium:phosphorus molar ratio of reactants and pH of reaction environment), after sintering at 1250°C, monophase, biphase, or triphase ceramics consisting of hydroxyapatite, β‐tricalcium phosphate, α‐tricalcium phosphate, and calcium oxide were obtained. The phase composition and properties—i.e., density, shrinkage, hardness, bending strength, and roughness—of the fractured surfaces of the isostatically re‐pressed sinters wer

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09013.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09014.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Organotin compounds were used successfully to prepare highly oriented SnO2thin films on glass substrates. Spray pyrolysis of tetra‐n‐butyltin(IV) and di‐n‐butyltin(IV) diacetate led to the deposition of [110]‐ and [200]‐oriented SnO2films, respectively. The oriented growth of these thin films occurred via three stages: (1) formation of SnO2nuclei, (2) crystal growth of SnO2with preferred orientations, and (3) further crystal growth normal to the surface of the substrate. The butyl and acetoxy groups of the organotin compounds facilitated [110]‐ and [200]‐oriented growth of SnO2thin films, respectively. The present model explains the oriented growth of SnO2thin films in terms of the relationship between the molecular structure of the starting compounds and the atomic configuration of the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09015.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effective piezoelectric moduli of polycrystalline piezoelectric ceramics are calculated using a straightforward averaging method (a Voigt average) and a more rigorous effective‐medium theory recently developed for piezocomposites. The effects of polarization orientation within each crystallographic domain and the shape of the domain on the effective piezoelectric moduli are presented. The effective‐medium theory, which includes full coupling of the elastic and dielectric interactions, gives results in reasonable agreement with experimental o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09016.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The yield stress of concentrated suspensions of alumina, zirconia, and mixed alumina‐zirconia powders was measured by the vane technique as a function of solids loading, relative amounts of alumina and zirconia, and pH. At the isoelectric point (IEP), the yield stress varied as the fourth power of the solids loading. The relative ratio of alumina and zirconia particles was important in determining the yield stress of the suspension at the IEP. The yield stress of single and mixed suspensions showed a marked variation with pH. The maximum value occurred at or near the IEP of the suspension. The effect of electrical double‐layer forces on the yield stress can be described on the basis of the Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory. A normalized yield stress—that is, the ratio of the yield stress at a given pH to the yield stress at the IEP predicted by this model—showed good correlation with expe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09017.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A series of strontium‐bearing dicalcium silicate (Ca2Si04solid solutions (C2S(ss)), (SrχCa1‐χ)2SiO4with 0.02 ≤χ≤ 0.10, was prepared and examined by powder X‐ray diffrac‐tometry. These crystals, heated in the stable‐temperature region of the α phase and then quenched in water, were composed of the β phase, with χ≤ 0.08, and the α'Land β phases, with χ= 0.10. With increasingx,the unit‐cell axes of the β phase expanded and the β angle became small with eventual increase in the unit‐cell volume. The Rietveld analysis of the β‐C2S(ss) with χ= 0.08 showed that the Sr2+ions preferentially occupied the seven‐coordinated site rather than the eight‐coordinated site. This site preference, which was originally established in the parent α‐phase structure, seemed to cause the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09018.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1996.tb09019.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY