ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15975.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Bicrystals containing symmetrical tilt boundaries with either theor thedirection as the rotation axis were vapor‐grown at 1740°C using the reaction 2AlCl3(g)+3CO2(g) + 3H2(g)→.Al2O3(s) + 6HCl(g) + 3CO(g). Specimens as large as 3 by 5 by 20 mm were produced in 24 h. Chemical purity of the specimens is high, with<0.1 ppm total cation impurities, as determined by activation anal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15976.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The double decomposition of hafnium and titanium tetrakis tertiary amyloxides was used to produce high‐purity stoichiometric submicron HfTiO4powders. The particle size range was 50 to 400 Å. X‐ray diffraction of a 1:1 mixture, as‐prepared and heated to ∼750°C, indicated that the material is 95% orthorhombic HfTiO4. The TGA, BET, DTA, and high‐temperature X‐ray analysis of the as‐prepared powders are also reported; the ir absorption and reflection frequencies of HfTiO4were determined. The homogeneity and stoichiometry of the powder were demonstrated by electron microscopy and wet chemical analysis. Mixed oxides prepared in this manner were sintered in an ambient atmosphere at 1650° to 1700°C for 4 h or Ionger into a body of nearly theoretical density and unifo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15977.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

High‐purity submicron HfO2−Y2O3powders were prepared by the simultaneous hydrolytic decomposition of hafnium and yttrium alkoxides. Compositions of 1 to 7 mol% Y2O3in HfO2were studied by high‐temperature X‐ray diffraction, electron microscopy, BET surface area measurements, emission spectrographic analysis, TGA, and DTA. X‐ray diffraction and atomic absorption were used to determine the Y2O3concentration. Hot‐pressing or cold‐pressing and sintering of the powders resulted in nearly theoretically dense bodies with uniform microstructure containing grains 1 to 5 μm in size. Surface reflection ir spectra were obtained for monoclinic, tetragonal, and cubic specimens. Fully cubic HfO2with 7 mol% Y2O3additions was obtained at a relatively low temperature. The hot‐pressed specimens, initially slightly oxygen‐deficient or gray HfO2‐x, were reoxidized at 1000°C with no deleterious effects; thin sections were transluc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15978.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Phase equilibrium relations in the celsian‐silica‐alumina portion of the system BaO‐Al2O3−SiO2were revised on the basis of data obtained from isothermal firing and from the quenching method. These data verify the existence of a celsian‐silica compatibility join by reducing the extent of the mullite field shown in previous diagrams and extending the boundaries of the celsian primary field. The system celsian‐silica‐alumina is divided into two ternary subsystems, one having a eutectic point and the other an invariant reaction point. The eutectic for the subsystem celsian‐silica‐mullite is located at BaO 19, Al2O315, and SiO266 wt% and 1296°± 3°C. The pertinent invariant point for the subsystem celsian‐mullite‐alumina, located at BaO 26, Al2O327, and SiO247 wt% and 1554°

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15979.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The phase diagram for the system Na3AlF6−AlF3was determined by quenching and microscopy supplemented with DTA and X‐ray powder diffraction. Primary crystallization fields for cryolite, chiolite, and aluminum fluoride are defined. Liquid containing 30 wt% AlF3is in peritectic equilibrium with solid cryolite and chiolite at 741°C; solid chiolite and aluminum fluoride are in equilibrium with liquid at the eutectic composition 39 wt% AlF3and 6

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15980.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The preparation, microstructure, and properties of BaZrS3ceramics are described. The compound was prepared by heating either an equimolar mixture of BaS and ZrS2or BaZrO3alone in CS2gas. The reaction of the BaZrO3−CS2system was extremely rapid, as would be expected in an autocatalytic reaction caused by very strong reduction by CS2. Well‐sintered bodies were obtained only by the BaZrO3−CS2reaction. The time dependence of grain growth was affected considerably when reaction and sintering occurred above 1250° C. Non‐uniform grain growth which occurs when an excess of Ba is present can be interpreted in terms of secondary recrystallization resulting from segregation of BaS at the grain boundary during sintering. The BaZrS3ceramic was stable in air up to 550°C and was oxidized above that te

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15981.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Sound velocities, densities, and lattice parameters of hot‐pressed bodies of the solid‐solution series Al2O3−Cr2O3were investigated. Measured lattice parameters deviated slightly from Vegard's law. The compositional dependence of the longitudinal sound velocity agreed well with the predictions of Birch; the observed dependence of the bulk modulus on ionic volume did not agree with the relation of Anderson and

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15982.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Creep behavior of polycrystalline A12O3doped with MgO + NiO, both as‐hot‐pressed in graphite dies and additionally annealed, was determined for 1300° to 1470°C and for 1000 to 15,000 psi in compression. The deformed specimens contained intergranular separations. Creep rates were proportional to stress to the 1.1 and 1.3 powers and were independent of grain size changes occurring during creep. The suggested creep mechanism is localized plastic deformation at stress concentration points accommodated by grain‐boundary separations initiated by grain‐boundar

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15983.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Separation of phases was investigated in the hexagonal (rhombohedral) systems Al2O3−Cr2O3and Al2O3−Cr2O3−Fe2O3. The binary system shows a miscibility gap with aTcof 950°C; the miscibility gap for the ternary system was determined for a constant Cr2O3content of 16.6 mol%. Dark field transmission electron microscopy of solid solutions annealed within the miscibility gap showed dark and light lamellas ∼50 to 200 Å thick. X‐ray diffraction results for the solid solutions in the ternary system indicated that, in the early stages of annealing, broadening occurred only on (hkl) reflections wherel≠0. There was no major change in the X‐ray diffraction patterns of the annealed solid solutions in the binary system. Electron diffraction results indicated, however, that phase separation in both systems proceeded in the [001] direction. Solid solutions in the binary system separated very slowly; the separation could be enhanced hydrothermally. The mechanism of the separation of phases in both systems is spinodal and proceeds as follows: solid solution→intermediate modulated phase

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1970.tb15984.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY