ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15107.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Devitrification occurs near the cathode when reconstructed high‐silica glasses and fused quartz undergo electrolysis at 900°C. The crystalline phase is cristobalite and results from a concentration of alkali ions. Subsequent and more superficial crystallization around the alkali‐rich spot is caused by interaction of the glass with alkali vapors coming from the central spot. The degree of devitrification increases with the alkali content of the glass. Devitrification at constant alkali level can be reduced in reconstructed glasses by nitriding the porous glass with ammonia at a high temperature before consolidation. Devitrification decreases and viscosity and electrical resistivity increase as the nitriding temperature increases 500° to 1000°C. Nitrided glasses are more resistant to electrolytically induced devitrification than is fused

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15108.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

The defect structure of high‐purity, polycrystalline HfO2was investigated by measuring the oxygen partial pressure dependence of the electrical conductivity and the sample weight. From 1000° to 1500°C and above oxygen partial pressures of 10−6, the conductivity is electronic and proportional topo21/5. The predominant defect is completely ionized hafnium vacancies. At lower oxygen partial pressures a broad shallow minimum in the lower temperature conductivity isotherms indicates the presence of an oxygen pressure independent source of electronic charge carriers. By combining the weight change and conductivity data, mobility values were found to vary from 1.6 × 10−3to 3 × 10−4cm2/V‐sec. The activation energies for the hole mobilities were calculated to be 0.2 ev above 1300° C and 0.7 ev below th

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15109.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Anodic tantalum oxide thin‐film capacitors have proved quite satisfactory for circuit applications, although some minor limitations exist in the maximum usable dielectric thickness, current asymmetry, and allowable counterelectrode materials. For this reason, two processes of glow discharge anodization and dc diode reactive sputtering were investigated for the formation of tantalum oxide films. Dielectrics up to a maximum thickness of 3000 A could be prepared by these methods with equal or larger than anticipated capacitance per unit area and dielectric strengths of about one third of anodically formed tantalum oxide. The dc diode reactive sputtering process produces thickness variations over 50 cm2of 4 to 20% compared with 4 and 1%, respectively, for glow discharge anodization and aqueous anodization. At the present time, the all‐vacuum methods are limited in applicability because of lower dielectric strength and lower formation ra

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15110.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Phase relations were studied in the system ZrO2‐MgO with emphasis on the range 1350° to 1600°C. A phase relation was determined from samples, using precision lattice parameters, X‐ray diffraction line intensities, and petrographic observations, and from dynamic observations of the phases present using high‐temperature X‐ray diffraction techniques. Limits were established for the solubility of MgO in tetragonal ZrO2and for the range of the cubic solid solution. The phase relations below 1240°C were complicated by hysteresis in the monoclinic to tetragonal inversi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15111.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

The hot hardness of TiB2, W2B5, ZrB2, HfB2, ZrO2, Al2O3, NbC, Tic, TaC1‐x, HfG1+x, (Ta0.8Hf0.2)C1+x, W2C, and (W0.65Cr0.14Re0.14Ta0.07)2C of<95% density was determined to temperatures approaching 1900°C. In all cases, the hardness decreased rapidly with increasing temperature. The data are compared to those available in the literatu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15112.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Manganese ferrite and α‐Fe2O3particles were precipitated within silicate melt systems to produce very unusual magnetic properties. Assemblies of particles of both kinds behaved super‐paramagnetically when the particle size was small enough. As the particle size was increased, the magnetic properties of the ferrite system increased, but those of the α‐Fe2O3system decreased; the latter is expected from Néel's theory of a net spontaneous magnetic moment created by uncompensated magnetic sublattices at very small particle sizes. Liquid‐in‐liquid phase separation was pronounced in the manganese ferrite‐glass systems, which may have influenced the precipitation behavior. Room‐temperature initial mass susceptibilities were as high as 2 × 10−2cgs, and specific magnetizations as high as 26 gauss/g were observed. Precipitation of α‐Fe2O3particles exhibiting super‐paramagnetic behavior was possible only with very low‐viscosity melts. Initial mass susceptibility values changed by as much as a factor o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15113.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

The effect of increasing BaO on the intensity and position of absorption bands induced in barium silicate glasses was studied. Many of these glasses showed a two‐step process in the growth and thermal bleaching curves. This process was attributed to two types of defects in the glass, induced and intrinsic. Infrared absorption, molar volume, and X‐ray diffraction studies predicted structural changes at compositions containing about 22.5 and 27.5 mole % BaO. The results of gamma‐induced absorption were in Une with these predictions, supporting the view that color center studies can be used to detect changes in structure, especially when high radiation doses are ap

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15114.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Some factors influencing the formation of thorium carbide from a mixture of thorium dioxide and graphite powder were studied. The effects of the molecular ratio of the reactants, reaction temperature, extrinsic properties (such as surface area, defects, and crystallinity of the materials), and the ambient pressure were examined. The molecular ratio of the reactants gave the most important effect on the composition of the final products. Thorium dicarbide was formed from a mixture having a molecular ratio (C/ThO2) of more than three and the reaction rate then obeyed the parabolic rate equation. To form thorium monocarbide, it is necessary to use a mixture having a ratio less than four. A tentative explanation of the reaction mechanism of ThC formation is given.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15115.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Calcium aluminate and calcium silicate hydrates were formed in mixtures of bentonite with water and various types of lime which had been sealed and cured for up to three years at 23°± 2°C and 100% relative humidity. Methods of analysis were X‐ray diffraction and electron microscopy. Hydrothermal treatment of the cured mixtures at 170°C for 12 hr produced well‐crystallized tobermorite with apparent lattice substitution of aluminum. The same result was obtained by hydrothermal treatment of identical uncured m

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1967.tb15116.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY