ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13431.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Multiorganometallic compounds were used to prepare high‐purity submicron‐size lead lanthanum zirconate‐titanate (PLZT) powders which can be consolidated at low sintering temperatures to high‐density piezoelectric and electrooptic ceramic bodies. Simultaneous hydrolytic decomposition of lead isoamyloxide, lanthanum isopropoxide, and zirconium and titanium tertiary amyloxides produced quaternary titanate powders with particle sizes of 75 to 300 Å and analyzed purity of 99.92%; the major contaminant was Na from an intermediate reaction product. Homogeneity and stoichiometry of the powders before and after processing were demonstrated by electron microscopy and chemical analysis. High‐temperature X‐ray diffraction indicated an amorphous material up to ∼600°C, where the crystalline phase was first observed. Powders prepared in this manner sintered to high‐density fine‐grained transparent bodies with uniform microstructure. The experimental results suggest that less rigorous consolidation methods are required with high‐purity homogeneous precursor materials wi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13432.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The optical absorption spectra from 200 to 2700 nm were determined for arc‐fused ThO2crystals of much higher purity than any available hitherto. The fundamental absorption edge for these crystals lies at a much higher energy (∼5.9 eV) than the apparent edge reported previously for less pure specimens. This apparent edge is shown to result from one or more prominent high‐energy absorption bands superimposed on the true edge for such specimens. By comparing the spectra for different specimens subjected to thermal and γ‐irradiation treatments, 31 distinct absorption bands were revealed in the ThO2spectrum. A full analysis of certain crystals by spark‐source mass spectrometry gave no strong correlation between specific band areas and individual impurity‐element concentrations. Most of the bands, however, are believed to be associated with the impu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13433.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Highly dense translucent polycrystalline bodies of stoichiometric aluminum silicate (mullite) were obtained by vacuum‐hot‐pressing of high‐purity submicron mixed oxide powders. The powders were prepared by the hydrolytic decomposition of mixed metal alkoxides. X‐ray diffraction and electron microscopy indicated that the initially amorphous needlelike fine particulates transform into highly crystalline orthorhombic mullite at ∼1200°C. Optimum hot‐pressing conditions were 5 kpsi and 1500°C for 30 min. Densities within experimental error of the theoretical value of 3.19 g/cm3were obtained. A typical microstructure consisted of fine interlocking needlelike grains arranged in an overall mosaic or “jigsaw” pattern. Microprobe traverses across the samples indicated homogeneous dispersion of SiO2in the AlO3matrix. Room‐temperature mechanical properties were measured and correlated with the microstructure and crystal structure of the ceramic compact. A slightly higher melting temperature than has been previously reported was observed for the 3Al2O3·2SiO2studied. All specimens exhibited a smooth surface finish and excellent thermal‐shock resistance from 1200

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13434.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Phototropic glasses in which TlCl crystallites play an active role were developed. When glasses containing Tl and Cl were reheated at 420° to 480°C for 3 to 20 h, phototropic glasses were obtained which were transparent, translucent, or opaque, depending on the temperature and time of heat treatment. X‐ray powder diffraction patterns of these glasses indicated the presence of TlCl crystallites. The optical absorption in the visible region which developed in the glass after uv exposure was similar to that developed in TlCl crystals prepared by melting TlCl powder. These facts suggest that the phototropy is caused by TlCl crystallites precipitated in the glass by heat treatment. Optical absorption was measured during both darkening and bleaching of the gl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13435.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The effects of stress, temperature, grain size, porosity, and O2partial pressure on the creep of polycrystalline Fe2O3were studied in the range 770° to 1105°C by tests in 4‐point bending and compression. Deformation rates are controlled by the stress‐directed diffusion of either oxygen or iron. Diffusion coefficients computed from the Nabarro‐Herring formula modified by including an empirical porosity‐correction term are also consistent with the values reported for oxygen

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13436.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Equilibrium partial pressures of SiF4were measured for the reactions 2SiO2(c)+2BeF2(d)⇋SiF4(g)+Be2SiO4(c) (logPsiF4(mm) = [8.790 ‐ 7620/T] ±0.06(500°–640°C)) and Be2SiO4(c) +2BeF2(d)⇋SiF4(g) +4BeO(c)(logPsiF4(mm) = [9.530–9400/T] ±0.04 (700°–780°C)), wherein BeF2was present in solution with LiF as molten Li2BeF4. The solubility of SiF4was low (∼0.04 mol kg‐1atm‐1) in the melt. The results for the first equilibrium were combined with available thermochemical data to calculate improved ΔHfand ΔGfvalues for phenacite (–497.57 ±2.2 and –470.22±2.2 kcal, respectively, at 298°K). The few measurements above 700°C for the second equilibrium are consistent with the temperature of the subsolidus decomposition of phenacite to BeO and SiO2and with the heat of this decomposition as determined by Holm and Kleppa. Below 700°C, the pressures of SiF4generated showed an increasing positive deviation from the expression given for the equilibrium involving Be2SiO4and BeO. This deviation might have been caused by the formation of an unidentified phase below 700°C which replaced the BeO; it more likely resulted from a metastable

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13437.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Magnesia‐doped alumina was fractured in a high‐vacuum Auger electron spectrometer, and the resulting intergranular fracture surface was analyzed for surface composition. Calcium was present on the fracture surface in amounts of ∼2 to 5 at.%. There was no indication of Mg on the fracture surface. The bulk Ca concentration was 5 to 15 ppm, whereas MgO was present at the 1000‐ppm level. The presence of excess Ca at the grain boundary can be explained by the fact that its ionic radius is relatively large compared to those of Al and Mg. Sputtering profiles normal to the fracture surface indicate that the segregated Ca is concentrated in a region near tha intergranular fracture

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13438.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The compressive creep of 18 mol% CaO‐stabilized ZrO2was studied at 1200° to 1400°C and 500 to 4000 psi. The specimens were polycrystalline with grain diameters from 7 to 29 μm. The activation energy for creep is 94 kcal/mol, and the creep rates are linearly proportional to the stress and to the inverse of the grain size. These results lead to the conclusion that creep in 18 mol% CaO‐stabilized ZrO2may be controlled by cation diffusion associated with grain‐boundary

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13439.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The free‐energy change for the reaction 2In(l)+3NiO(s) = In2O3(s)+3Ni(s) was determined from 550° to 800°C from emf measurements on solid‐oxide galvanic cells. The results were used to develop an equation for the standard molar free energy of formation of In2O3, i.e. ΔG°ln2O3= ‐215,550+72.63T±450 cal/ mol. The standard molar enthalpy and entropy of formation of In2O3at 298°K were calculated to be ‐214,000±1500 cal/mol and ‐69.03±o0.22 eu, respectively, using the available thermo‐chemical data. The absolute entropy of In2O3at 298°K was calculated to be 32.23±0.22 eu. The free‐energy results of this study were used in conjunction with literature data to calculate partial pressures of the gaseous species over In2O3for different

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb13440.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY