摘要:

Amorphous WO3or WO3or H2O is formed by hydrolysis of tungsten ethoxide. The temperature of hydrolysis influences the crystallization of WO3·H2O. Tungsten hydrate (WO3·H2O) has an orthorhombic unit cell with a=0.5235 nm, b = 1.0688 nm, and c=0.5123 nm. Orthorhombic WO3crystallizes at 350° to 500°Cfrom amorphous WO3. Cubic WO3is formed at 200° to 310°C with dehydration of WO3·H2O. WO3transformations are examined by high‐temperature X‐ray diffraction. The kinetics of formation of the cubic modification have been studied by measuring the weight decrease with a thermobalcnce. Formation isotherms can be interpreted in terms of the first‐order equation –In (1–f)=kt; activation energies are 110 and 80 kJ mol−1for initial and final st

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05010.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A compound tentatively denoted as Zn2Ti,3O8is determined to be a low‐temperature form of ZnTiO3. At a heating rate of 10°C·min−1the low‐temperature form crystallizes at 600° to 765° C from an amorphous material prepared by the simultaneous hydrolysis of zinc acetylacetonate and titanium isopropoxide. It has a cubic unit cell with a =0.8408 nm. The cubic‐to‐hexagonal transformation occurs slowly above 820°C; during transformation ZnTiO3decomposes into Zn2TiO4and TiO2(rutile) at 965° to 1010°C. A single phase of the hexagonal form can be prepared by heating for 5 h at 900°C. The structure of both forms consists of octa

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05011.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Pure cubic perovskites Ba(Na2/5W3/5)O3, Sr(Na2/5W3/5)l5)O3, and Sr(Li2/5W3/5)O3were prepared by solid‐state reaction at 600° to 650°C in air, by starting with oxides or carbonates of the various elements. The cubic forms have an ordered arrangement of the B cations in the ABO3structure, and the lattice constants are a =0.8324 nm [Ba(Na2/5W3/5)O3], 0.8136 nm Sr(Na2/5W3/5)O3], and 0.7958 nm [Sr(Li2/5W3/5

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05012.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The glass‐forming region in the ZnO‐Al2O3‐SiO2system was studied, and the acid resistivity of the glass stabilized by PbO addition was measured. Glass containing more than 50 at.% SiO2 had a markedly increased acid resistivity. At about 50 at.% SiO2, the crystallization of the glass caused its resistivity to dec

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05013.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The frictional properties of sintered TiN‐TiB2and Ti(CN)‐TiB2ceramics were investigated in air at temperatures up to 1073 K. Friction coefficients as low as 0.1 to 0.2 can be obtained at 973 to 1073 K because oxidation of TiB2produces a lubricating, glassy phase of boron oxide on the sliding surfa

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05014.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Mg‐Si‐O‐N glasses were used to bond dense Si3N4ceramic pieces by a liquid‐phase diffusion bonding mechanism. In this case, it was difficult to achieve defect‐free bonding because, at low nitrogen content in the glass, a large mismatch in thermal expansion coefficient produced cracks perpendicular to the bonding glass layer. With an increase in nitrogen content, the glass layer became frothy and contained “bubbles.” However, when a small amount of elemental silicon was added to the glass, volatile reaction was suppressed and intimate bonding was achieved without t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05015.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A discussion of the relative merits and problems of using Ba(OH)2, BaO, and Ba as starting materials for the synthesis of barium titanate by the alkoxide method is presented. The Ba(OH)2process is promising because it does not involve the synthesis of barium alkoxide, whereas the BaO (93% pure) process suffers from complex chemical reactions; the impurities in BaO cause unknown effects on the composition and properties of the final ceramic. Use of high‐purity Ba metal (99.99%) for the synthesis of barium alkoxide is more desirable since it results in high‐purity, ultrafine barium titanate powd

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05016.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Thermal shock testing of an alumina‐20 vol% SiC whisker composite showed no decrease in flexural strength with temperature differences up to 900°C. Alumina, on the other hand, normally shows a significant decrease inflexural strength with a temperature change of>400°C. The improvement in the thermal shock resistance of the composite is believed attributable to the increased fracture toughness of this mater

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05017.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Sodium β‐Al2O3changes its molar volume upon ion exchange. This effect can be utilized to introduce surface compression into brittle matrices. Experiments are reported wherein spinel/20 vol% Na‐β‐Al2O3and glass/20 vol% Na‐β‐Al2O3composites containing constrained Na‐β‐Al2O3particles underwent Na+to K+ion exchange in KNO3melts and thereafter exhibited shorter Vickers microi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05018.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Oxycarbide glasses in the Mg‐Al‐Si‐O‐C system and oxynitride glasses in the Mg‐Al‐Si‐O‐N system were synthesized by conventional melting techniques, chemically analyzed, and evaluated for selected mechanical properties as a function of carbon or nitrogen content. Both glass systems exhibited increases in density, Young's elastic modulus, microhardness, and fracture toughness with increasing anionic substitutions. Carbon substitutions were found to be more effective than nitrogen additions for improving g

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1987.tb05019.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY