ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11891.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The vaporization of lead monoxide from lead zirconate‐lead titanate materials was studied by thermogravimetric techniques in vacuum with hot‐pressed pellets of near theoretical density. The initial step of the complex, two‐step vaporization observed in cold‐pressed pellets in an earlier investigation is absent. The rate‐determining step for both the porous, cold‐pressed, and pore‐free, hot‐pressed materials is the bulk diffusion of lead across a thickening lead‐depleted layer at the surface of the pellet and results in a parabolic time dependence. Although parabolic rate constants are slightly lower overall for the dense materials, the activation energies for the weight loss process remain approximately 38.5 and 35 kcal/mole for the pure and Bi‐doped Pb(Zr0.65Ti0.35)O3compositions, respectively. Vaporization mechanisms and rates were unchanged under nitrogen or oxygen pressures up to 50 torr at 1000°C. Alumina Knudsen cells were used to study the equilibrium vapor above a powdered, hot‐pressed Pb(Zr0.65.Ti0.35)O3composition. Mass spectrometric analysis of the vapor at 950°C showed that the vapor species and their relative abundances were the same as the equilibrium vapor species above pure lead monoxide. Continuous weight loss data from these cells gave an apparent vapor pressure that was 2% of the vapor pressure of pure lead monoxide at a given temperature, but gave the same second law enthalpy of vaporization. The overall vaporization process can be represented by the reversible equilibria: the diffusion of Pb2+and O2‐ to the surface through a lead‐depleted region whose phases and compositions are determined by the subsolidus phase relations in the PbO‐ZrO2‐TiO2ternary system, the reaction at or near the surface to form PbO, and the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11892.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The CrO2‐Cr, O3equilibrium curve has been determined up to 35 kbars and 1400° C with a piston‐cylinder apparatus. The phases were determined by magnetic, X‐ray, and microscopic examination. The phase boundary can be represented by a straight line logPversus1/Tplot, where logP= 5.3 ‐ 1400/T.These results can be extrapolated to agree reasonably well with the results of previous investigations using gas pressure te

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11893.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

A procedure is presented for growing single crystals of (PbxSr1‐x)TiO3by passing solvent zones through poly‐crystalline rods of the same composition (THM). The solvent zone composition for homogeneous solid solution growth was chosen from the pseudoquaternary system 2PbO: 1B2O3‐2SrO:1B2O3‐PbTiO3‐SrTiO3. Crystals with compositions throughout the complete range of PbTiO3‐SrTiOs solid solutions were grown. Emphasis was placed on crystal compositions near (Pb0.25Sr0.78) TiO3which have Curie temperatures just below room temperature. The dielectric constants, Curie temperatures, and optical properties of these single crystals are presented. Nonlinear dielectric and electrooptic behaviors are also d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11894.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The thermal properties of PUP and PUS were measured from room temperature to 650° C by a heat‐pulse technique. Disk‐shaped specimens of 90% theoretical density were made by isostatic cold‐pressing and sintering. The thermal conductivity of PUP corrected to theoretical density ranged from 0.014 cal sec‐cm‐1°C‐1at room temperature to 0.019 at 650° C. Over this temperature range the heat capacity increased from 0.055 to 0.056 cal g‐l°C‐1. The thermal conductivity of PUS decreased approximately 16% from its room temperature value of 0.023 cal sec‐cm‐1°C‐1and then rose to 0.037 at 650°C. The temperature dependence of the thermal conductivity of PUP is apparently related to the quasimetallic electrical properties of this compound. PUS is a semiconductor and the rise in its thermal conductivity (after passing through a minimum) may be partly attributed to a bipolar

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11895.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The theory of grain growth in the presence of a liquid phase is examined using modifications of equations derived for coalescence of solid particles widely dispersed in a liquid. Although the grain diameter‐time relation can still be represented byd3=kt, the absolute growth rates are increased as the amount of liquid is decreased. The grain growth kinetics in UO2compacts containing 0.5 wtyo A12O3were studied for temperatures between 1960° and 2200°C. The interrelation of grain size, temperature, and time is in agreement with that predicted by the the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11896.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The phase boundaries of subliquidus immiscibility in the lithium, sodium, potassium, rubidium, and cesium borate systems were determined. Two‐phase structures were developed in thermal gradients and examined by direct‐transmission electron microscopy. No opalescence was observed. Microstructures were of the order of a few hundred angstroms. The extent of immiscibility in each system was determined by the approximate intersection of the immiscible phase boundary with the glass transition reg

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11897.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The kinetics of crystallization of Li2Si2O5from glasses in the Li2O‐SiO2system were studied using quantitative X‐ray diffraction. Analysis of the data using the Johnson‐Mehl‐Avrami equation showed that crystallization occurred through the nucleation and growth of rods. The spherulitic nature of the crystals was substantiated by petrographic examinations of the partially crystalline glass. Analysis of the temperature dependence of the crystallization rate using a modification of the Johnson‐Mehl‐Avrami equation showed that the activation energy for nucleation was a function of composition and therma

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11898.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

A quantitative microstructural study of the deformation of flexible sandstone confirms the “loose‐grain” model of the deformation behavior of this composite material. The study demonstrated the contribution of the micα‐quartz intergrowth to the bonding and confirmed that the role of mica in the flexibility of the composite is negligible. The microstructural evidence indicates that the quartz‐mica bond must have resulted from in situ growth of mica simultaneously with growth of qua

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11899.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The cation‐defective NiAs‐type polymorphs of MnCr2S4, FeCr2S4, and CoCr2S4were prepared by high pressure‐high temperature heat treatments. The magnetizations of these specimens and NiCr2S4were studied from 1.5'K to room temperature. All phases with the NiAs‐type structure were antiferromagneticalIy ordered below NBel temperatures of 70°, 200°, 300°, and 200°K, respectively. These data show a transition from ferrimagnetic to anti‐ferromagnetic ordering in the transformation spinel‐type ↔ NiAs‐type structure in th

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11900.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY