摘要:

On heat treatment in air the solubility of MgO or TiO2, in Al23is too small to detect by lattice parameter shifts. The solubility of MgTiO3in Al2O3in air increased to the measured values, expressed as atomic fractions Mg:A1or Ti:A1of0.82 × lo‐2, 1.43 × 10‐2, and 1.75 × 10‐2at 1250°, 1650°, and 1850°C, respectively. In 1 atm hydrogen the TiO2solubility expressed as the atomic fraction Ti:A1 is 0.55 × lo‐2, 0.75 × 10W2, 1.15 × 10‐2, and 1.50 × 10p2at 1400°, 1500°, 1600°, and 1700°C, respectively. The increased solubility in H2was attributed to reduction of the titanium ion. The solubility of MgO in A12O3in vacuum(0.3μ)expressed as the atomic fraction Mg:A1 was measured as 1.10 × loW4, 3.00 × 10”4, 6.80 × 10–4, and 1.40 × 10‐3at 1530°, 1630°, 1730°, and 183O°C, respectively. These contents did not cause an observable change in lattice parameter, but a slight change was observed when MgO was diss

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13316.x-i1

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Pressures of nitrogen over UN(s) + U(1) were measured between 1300′ and 1500°C. These data, coupled with literature data, extend the measured range of pressures to nearly 11 orders of magnitude and 1550 centigrade degrees. The best value of AH°298, UN from the available data is taken to be ‐69.6 +1.0 kcal/mole. The second and third law calculations agree satisfact

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11818.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Polycrystalline spinel (MgA12O4), hot‐pressed in graphite dies, yielded densities ranging from ∼64 to ≊100% of theoretical. Average grain size of compacts varied from 4 to 125μ depending on hot‐pressing conditions. Room‐temperature mechanical properties also varied widely; average strengths for the 15 experimental combinations ranged from 3500 to 34,000 psi in bending and from 21,700 to 389,000 psi in compression, and Young's modulus ranged from 0.54 X lo7to 3.5 X 107psi. Variations in bulk density, average grain size, room‐temperature transverse and compressive strengths, and Young's modulus of elasticity were separately expressed as multiple quadratic regressions in terms of 1/T (temperature), In t (time), andP(pressure) over the hot‐pressing range 1227’to 1750°C, 5 to 320 min, and 1000 to 3000 psi. From these regressions, empirical equations expressing mechanical properties in terms of regression solutions of density and grain size were derived which statistically indicate a principal dependence on density and only a minor grai

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11819.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Using the phase diagram and a simple solution model, a subliquidus miscibility gap was estimated for the B2O3‐SiO2system. The predicted coexistence boundary, showing a consolute temperature of 520°C, was flat and symmetrical and extended across the complete binary. Gradient furnace heat treatments of selected compositions in this system resulted in phase separation which corresponded closely to the coexistence boundary initially predicted. Calculations and preliminary experimental results indicate that temperatures and compositions exist wherein metastable three‐liquid immiscibility occurs in R20–B203‐SiO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11820.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The effect of water vapor on the initial sintering kinetics of calcium oxide was studied at 920” to 1123°C. In the range of PHI() from 8 × 10W4to 487 mm Hg, water vapor increased the rate of sintering. The initial sintering kinetics followed the model for volume diffusion with calculated diffusion coefficients dependent onPH2O, which varied from (P,H2O)1/2at pressures between 6.1 and 50 mm Hg to (PIH2O)1/2at pressures between 244 and 487 mm Hg. The activation enthalpy varied from 123 ± 7 kcal/mole when PH2O= 0.04 mm Hg to 103 ± 3.5 kcal/mole at PH2O243.9

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11821.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The ZrO2‐HfO2system was investigated by metallo‐graphic, X‐ray diffraction, and microprobe analysis using are‐melted samples which had been annealed and quenched. The monoclinic‐tetragonal inversion was investigated by DTA and high‐temperature X‐ray diffraction analysis. Results reveal that zirconia and hafnia are completely miscible in all proportions in the binary system. Within experimental error, the melting points of the compositions lie roughly on a straight line connecting the melting points of oxides. There is a continuous increase in the monoclinic‐tetragonal inversion temperature as the composition moves from ZrO2to HfO2. The lattice parameters of the monoclinic phase follow smooth curves which have a negative deviation fr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11822.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Glasses in the system Pb0–Al2O3‐B2O3‐SiO2are chemically stable over a wide composition range and have very desirable electrical characteristics such as high electrical resistivities and activation energies for conduction. Variations in these electrical properties were studied as a function of composition changes within the system, the object being to identify the role of the constituent oxides in achieving the highest activation energy and resistivity values consistent with moderate preparation temperatures. Measurements were made in the temperature range 25° to 400°C on carefully prepared glass disks in which the individual oxide components or different oxide ratios such as PbO/SiO2, Al2O3/SiO2, and BsO3/SiO1were systematically varied. The activation energy and resistivity values obtained ranged from 1.2 to 1.6 ev and 10° to 1014ohm‐cm, with dielectric constants ranging from 9 to 19 and densities from 4.30 to 4.50 g/cmY. Indications were that, for the composition range studied, the behavior manifested was basically that of the binary PbO‐SO2glass with additions of Al2O3or B2O3, even in small concentrations, sharply increasing the activation energy for conduction while lowering

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11823.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The heat transfer processes in the growth of single crystals in a verneuil plasma torch were investigated. Heat transfer from the plasma to the crystalline boule was enhanced to a substantial degree by recombination of dissociated diatomic gases in the region of the boule tip. Boule tip temperatures were affected by the location of the boule in the plasma, distance of the boule from the powder probe, the feed rate and grain size of the powder being fed, the rf plate power of the generator, and the powder gas flow rate. Boule temperatures depended critically on heat loss by radiation from its side. It is predicted that refractory crystals require higher plasma input power as the boule becomes longer, if crystal growth rate is to be maintained.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11824.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Stabilized zirconias exhibit pronounced photoelastic effects when viewed with transmitted polarized light. Thin sections reveal stress concentrations around pores and inclusions and at grain boundaries. The yield point of these materials, at some high temperature, is exceeded and plastic deformation tends to relieve these stress concentrations. The microhardness measurements of magnesia‐stabilized zirconia indicate both solution hardening and solute segregation and help to explain the physical behavior of this system as the amount of MgO is varie

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11825.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

An isothermal section of the ternary system MgO–Al2O3‐Cr2O3was determined at 1700°± 15°C to delineate the stability field for spinel crystalline solutions (cs). Crystalline solutions were found between the pseudobinary joins MgAl2O4–Cr2O3and MgCr2O4‐Al2O3, and the binary join MgAl2O4‐MgO. The first two crystalline solutions exhibit cation vacancy models while the latter can probably be designated as a cation interstitial model. Precipitation from spinel cs may proceed directly to an equilibrium phase, (Al1‐xCrx)2O3, with the corundum structure or through a metastable phase of the probable composition Mg(Al1‐xCr)26O40. The composition and temperature limits were defined where the precipitation occurs via metastable monoclinic phases. The coherency of the metastable monoclinic phase with the spinel cs matrix can be understood by considering volume changes with equivalent numbers of oxygens and known crystallographic orientation relations. Electron probe and metallographic microscope investigations showed no preferential grain bounda

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11826.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY