ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15653.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

The high‐temperature transition monoclinic tetragonal in the rare‐earth tantalates and niobates with the formula AB04 was investigated using a high‐temperature X‐ray diffractometer. The transition was reversible and proceeded by a gradual change in symmetry. The temperature of the first appearance of the tetragonal phase increased as the ionic size of the rare‐earth ions decreased and was considerably higher for the rare‐earth tantalates than for the rare‐earth niobates. The mechanism of the change

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15654.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

The ternary system U‐C‐O was investigated and a diagram is given expressing the phase relations in specimens which were reacted at 1800°C in vacuum or in inert atmospheres and furnace cooled. A U(C,O) single‐phase area exists in this diagram. The limit of substitutional solid solution of oxygen atoms for carbon atoms in UC is 12.5 at.%, which means that only 25% of the carbon atoms in UC can be replaced by oxygen atoms. The oxygen‐saturated UC phase, U(C0.75O0.25), has a lattice parameter of 4.953 ± 0.001 A. The carbon monoxide partial pressures in equilibrium with this phase were determined for temperatures between 1705°

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15655.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Grain‐boundary diffusion of Ni2+was investigated in polycrystalline MgO and also in isolated grain boundaries in natural and prepared bi‐crystals of MgO. Concentration distributions were determined with the aid of both electron microbeam probe spectroscopy and X‐ray absorption analysis. Results from diffusion couples in which a surface was maintained at constant concentration during the diffusion annealing indicate that grain‐boundary diffusion is the predominant transport mechanism in polycrystalline MgO at temperatures below 1700°C. Lattice diffusion becomes increasingly important at higher temperatures and eventually becomes the dominant mechanism. Concentration distributions for diffusion couples in which a fixed amount of NiO was supplied to the surface of the couple as a thin initial plating resemble those for lattice diffusion but yield anomalously high values for apparent lattice diffusion coefficients. Grain‐boundary diffusion in MgO is not confined to a layer of atomic dimensions but extends over a zone of the order of microns. The activation energy for grain‐boundary diffusion is less than that for lattice diffusion and is between 1 and 2 ev. Grain‐boundary diffusion was observed even in tilt boundaries with a mismatc

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15656.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

The thermal conductivity of titanium carbide, zirconium carbide, and titanium nitride was measured by a variety of techniques in the temperature range 200° to 2000° C. The titanium nitride results are a factor of four higher than the previously published values at 1000°C and show a positive temperature coefficient for the thermal conductivity rather than the negative coefficient previously reported in other work. Recent thermal conductivity data on Tic confirm earlier data obtained by the writers which differed from previous literature values. Contemporary theory fails to explain the temperature dependency of the phonon and/or electron contribution to the heat conduction in the refractory interstitial compoun

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15657.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Properties of a metastable ferroelectric NaNbOa phase are described. This ferroelectric phase was induced by the application of a field greater than 50 kv per cm at a temperature in excess of 100°C. The ferroelectric state was evidenced by a spontaneous polarization of the order of 30 microcoulombs per cm2 and by fairly strong piezoelectric coupling. The ferroelectric phase, once induced, was stable with time and up to 270°

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15658.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Densification of silica glass was carried out at IS kb and 2000°C and of boron oxide glass at 20 kb and 900° C. The subsequent annealing of the densified glasses was examined at atmospheric pressure. The annealing behavior of glasses densified in the nonrigid condition is shown to be drastically different from that of the rigidly densified materials. The annealing kinetics are discussed in terms of two different processes of volume flo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15659.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Chemical polishing and etching techniques were used to reveal the dislocation structures of sapphire and ruby crystals grown by the flame‐fusion and flux techniques. The average density of edge dislocations lying in prism planes was 3.0 × 105per cm2, which could be changed only slightly by chromium additions and annealing at 2000°C. An average basal dislocation density of 2 × 105per cm2decreased 35 to 80% on annealing. Crystal orientation (i.e., angle between thecaxis and the growth axis) showed no effect on dislocation density but a pronounced effect on subboundary arrangement and density. The substructure of 0° crystals was more complex than that of 90° crystals; 60° crystals possessed a structure intermediate between 0° and 90°. Principal observations included (1) prismatic and basal slip on all as‐grown crystals; (2) profuse basal slip, readily polygonized on annealing; (3) dislocation densities of flux crystals lower than those of Verneuil crystals; and (4) a rare form of basal twinning, composition plane, on all fl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15660.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

The electrical properties of BaZrO3containing 2 to 6 at. % La were investigated. Room‐temperature dielectric constants at 1 Mc were about 43 and the mean temperature coefficients ofKwere about −240 ppm per °C. The admixture of La3+raised the volume resistivity by several orders of magnitude. Values as high as 10° ohm‐cm were observed at 500° C.Qvalues at 1 Mc and 500° C ranged between 100 and 400. Wafers 10 mils thick endured 1000‐hour life tests at 250° and 350°C in a field of 60 volts per mil and at 500°C in a field of 30 volts per m.il with good stability. Breakdown strengths as high as 680 volts per mil were measured for specimens 10 mils thick. The mechanism of conduction was indicated to be P‐type, with La3+improving resistivity by lowering the ho

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15661.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

The chemistry of the reaction between molten aluminum alloys and some refractory oxides is discussed. High‐alumina brick containing 85, 94, and 99% Al2O3periclase brick, and magnesia spinel brick were immersed for 48 hours in three aluminum alloys containing 0, 2.4, and 7.7% magnesium, respectively. All brick were discolored, although most of the discoloration disappeared after reheating at 1000°C in an oxidizing atmosphere. Only the 85 and 94% brick, which contained silica, showed permanently darkened reaction rims. X‐ray diffraction analysis of these darkened areas showed that the alloy containing 7.7% magnesium caused periclase formation in the rim whereas the alloy containing 2.4% magnesium produced spinel. Commercial aluminum caused only a decrease in the mullite content of the darkened area. Magnesia spinel and periclase were unaffected by all the alloys te

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1964.tb15662.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY