ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13245.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Single crystals of corundum and ruby were grown from PbF2‐Bi2O3melts. Their habits and the use of La2O3as a growth modifier are described. Lanthanum ions were incorporated into the growing crystals to promote the growth of equidimensional crystals. The habit modifications are interpreted as resulting from impurity adsorption on the steps on the {1011} faces and direct adsorption on the {0112} faces. The crystals grown from these melts are of good optical quality and contain few dislocation

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13246.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Single‐crystal and polycrystalline films of Mg‐Al2O4and MgFe2O4were formed by two methods on cleavage surfaces of MgO single crystals. In one procedure, aluminum was deposited on MgO by vacuum evaporation. Subsequent heating in air at about 510°C formed a polycrystalline γ‐Al2O8film. Above 540°C, the γ‐Al2O, and MgO reacted to form a single‐crystal MgAl2O4film with {001} MgAl2O4‖{001} MgO. Above 590°C, an additional layer of MgAl2O4, which is polycrystalline, formed between the γ‐Al2O3and the single‐crystal spinel. Polycrystalline Mg‐Al2O4formed only when diffusion of Mg2+ions proceeded into the polycrystalline γ‐Al2O3region. Corresponding results were obtained for Mg‐Fe2O4. MgAl2O4films were also formed on cleaved MgO single‐crystal substrates by direct evaporation, using an Al2O3crucible as a source. Very slow deposition rates were used with source temperatures of ∼1350°C and substrate temperatures of ∼800°C. Departures from single‐crystal character in the films may arise through

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13247.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

The permeability to oxygen of 4 wt% lime‐stabilized zirconia and hafnia and of pure thoria was determined between 1100° and 2050°C. The permeability constant (permeability multiplied by the thickness) at 25 torr oxygen pressure is given by:A 1/4‐power oxygen pressure dependence of the permeability was found for zirconia and hafnia and a variable power dependence was found for thoria. The diffusivities for zirconia and hafnia were determined from the time dependence of permeation. These are given by:A transport mechanism suggested for zirconia and hafnia involves migration of oxygen ion vacancies and electron

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13248.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Self‐diffusion of Zr in 12 and 16 mol.% CaO and of Ca in 16 mol.% CaO cubic zirconia was measured by the sectioning technique from 1700° to 2150°C. Lattice self‐diffusion coefficients are:Autoradiographs show rapid grain boundary diffusion.DBis estimated as<105DLbetween 1800° and 2150°C. The low cation self‐diffusion coefficients are compared with the high anion rate, and their effect on the diffusion‐controlled properties of zirconia i

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13249.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Pressed compacts of sized alumina powders were studied to determine the dependence of strength of compacts as sintering begins and proceeds through the initial stage. By carefully controlling the time and temperature of heat treatment in a helium atmosphere, it was determined that the strength‐controlling feature of these porous compacts is the area of the interparticle boundaries. Under isothermal conditions the strength was approximately proportional to time of sintering to the 2/7 power as described by theory. From these relations, it is possible to develop the semi‐empirical relation between strength and porosity that predicted zero strength at a porosity equivalent to the unfired condition of the powder compact. Although not a confirmation of the grain boundary sintering model, the strength and porosity data are more consistent with the grain boundary diffusion model for initial sintering of alumina than with bulk diffusion mod

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13250.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Rheological and electrokinetic properties of glass‐frit and quartz suspensions were investigated using a modified Gardner mobilometer and a microscope‐type electrophoresis apparatus. Variables included particle size distribution, aging, and extent of flocculation. Particle size considerably affected the rheological state of the suspensions, whereas, electrolyte addition (flocculation) greatly altered both the rheology and the electrokinetics. Aging of deflocculated suspensions decreased both apparent viscosity and zeta potential, whereas aging of flocculated suspensions decreased apparent viscosity and increased zeta potential. Explanation of the results is based on ion leaching or particle solubility, or both, insoluble silicate formation, number of charge sites per particle, and particle solvat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13251.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Magnesium ferrite varies in cell size, density, and refractive index, according to the temperature from which it was quenched, over the range 350° to 950°C. There is no evidence for long‐range ordering, but the change toward a more inverse structure with decreasing temperature is toward a more ordered state. The DTA tracing shows a strong exothermic peak at 450°C. The effect of the cooling rate on the thermal contraction of magnesium ferrite is discu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13252.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

A large glass‐forming region was discovered in the system EUO–Al2O3–B2O3and chemically stable glasses of good optical quality were produced. The concentration range extends from about 3 to 43 mole % EuO. Room‐temperature Verdet constants as large as –2.55 min/oe‐cm were measured on a glass containing 30.5 mole % Eu2+. This is somewhat higher than those reported for the trivalent rare‐earth ions in similar glass matrices. The effective transition wavelength causing the rotation is 380 ± 20 mμ. Compared to Ce3+, Tb3+, and Pr3+the large rotation of Eu2+in the visible region is due primarily to a largeJ(total angular momentum) value as well as to a large effective transi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13253.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Dense polycrystalline (p‐type) SiC undergoes viscous deformation between 1900° and 2200°C at stresses up to 30,000 psi. A boundary diffusion mechanism is assumed to be rate‐controlling; the product of the boundary diffusion coefficient,Db, and the boundary width,W, calculated from the creep d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1966.tb13254.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY