ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11018.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Construction details of a petrographic microscope modified for high‐temperature investigations are described. Operational features and specimen preparation procedures are discussed. The equipment has an optical system that provides a magnification of X70 with means for recording the results photographically. The maximum operating temperature is 2000°F. Typical photomicrographs of crystals developed in soda‐lime container glass at elevated temperatures are shown along with a crystal growth rate curve of crystalline phases in this g

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11019.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Rates of crystallization of Li2O · 2SiO2, from an Li2O · 4SiO2glass as a function of platinum concentration at 600° and 650° C were determined. At both temperatures a maximum rate was obtained in the region of 0.005% Pt. Calculations of the activation energies for the crystallization process showed that 0.005%, Pt lowered it to less than half its original value of 120 kcal per mole. Electron microscopy of this glass quenched from 1450OC revealed a granular structure 250 A in size which was believed to be due to lithium‐rich clusters in the glass, svpporting the concepts of other investigators. In glasses containing 0.025%, an additional phase identified as silica O was found. Explanations for the effectiveness of platinum as a nucleating agent in this glass are of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11020.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

It has been discovered that the formation of the butterfly twin in barium titanate depends on both the average particle size and the particle‐size distribution of the starting material. Maximum twin yields occur when the particles have an average size near 1μ with a rather sharp cutoff in the distribution in the large‐particle region. All impurities act to decrease twin yield, principally because they interfere with stacking‐fault formation which also is necessary for twinning to

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11021.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Analyses of natural minerals suggest the wide variety of both cationic and anionic substitutions possible in the pyrochlore structure. Limits on the possibilities of ionic substitution in pyrochlore have been determined by the preparation of a large number of compounds. An important feature found is that substitution of up to two of seven anions is possible but apparently no more. Many ion‐deficient structures can be made, especially those with one large cation absent. Anion deficiency to the same extent or even in smaller amounts leads to the formation of perovskite structures. Quantitative data on solid solubility among three related structures, pyrochlore, perovskite, and columbite, have been determined for the case of Cd2Nb2O7‐NaNbO3‐CdNb2O6. An attempt has been made to study the relation of pyrochlore and C‐type rare earth to the fluorite structure as an example of the ordering of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11022.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

An orthorhombic dipyramidal form and an orthorhombic lath‐shaped form of UO3monohydrate were grown hydrothermally. Optical and X‐ray constants were determined for these crystalline modifications. The X‐ray data corroborated previous data reported by Zachariasen for the orthorhombic laths and by Dawsonet al. for the dipyramidal form. An unreported phase transformation was observed to take place in the orthorhombic dipyramidal phase on the application of pressure. Optical and X‐ray examinations of the new phase showed it to be identical to the orthorhombic lath phase. The transformation appeared to fit Buerger's “displacive transformation” classification. Optical observations made on partly transformed dipyramidal crystals lying on their (001) faces showed the two phases, i.e., the dipyramidal phase and the new phase, joined along a (11.l) dipyramid plane. The displacive movement appeared to have taken place in a (110) dipyrami

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11023.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Rates of diffusion of Co2+and Ni2+ions in the MgO lattice were determined by a micrographic method. The energies of activation for the transport process were 65 and 36 kcal per mole, respectively. The penetration curve in these systems exhibited a plateau followed by a sudden decrease in concentratior.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11024.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Surface features observed on the faces of synthetic garnets grown from lead oxide‐lead fluoride melts are described and interpreted in terms of growth processes. The growth processes involve (1) nucleation of new growth layers at corners and edges between crystal faces and (2) propagation of layers associated with growth systems located on the crystal faces. Growth systems on the faces of crystals that terminated growth at about 1000°C appear as growth hillocks. Continuing growth to lower temperatures produces large vicinal faces, which result from the propagation of polygonized growth steps associated with a single, dominant growth system. Growth steps on the vicinal faces in turn possess faces that are parallel to the nearest adjacent crystal faces. Growth spirals have been observed on the faces of crystals that were grown slowly by evaporation of flux. Several observations, including the presence of growth spirals, the nature and location of line imperfections and hollow tubes, and the etching behavior of crystal faces and polished sections, are interpreted as evidence in favor of a latter‐stage growth mechanism that involves the propagation of steps associated with screw dislocat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11025.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Grain growth was investigated in a UO2sinter of 94%) theoretical density over the temperature range 1555° to 2440°C. The results were in close, but not exact, agreement with a theoretical expression describing grain growth with a poly‐crystalline matrix. For the material studied the mean grain diameter D (μm) after annealing for t hours at a temperature T (°K) was given by the equationwhere D0and K0are, respectively, the initial grain size and a proportionality constant. Uranium metal was found in all specimens annealed above 2000°C. This was taken as evidence that the UO2lattice can be oxygen‐deficient at high temp

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11026.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

Evidence is presented which shows that columnar grains can be induced to grow in high‐density sintered uranium dioxide specimens by applying a steep temperature gradient at temperatures above 1700°C but below the melting point of 2800°C. Columnar growth apparently is a result of the migration of large transverse voids, whose individual widths define the cross sections of the grains, up a temperature gradient by a sublimation process. The grains grown by this process have a (111) preferred orientation along their columnar axis. A consequence of such void migration in operating fuel elements containing solid UO2pellets is the formation of a central void bounded by a region of oxide exhibiting columnar gro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1962.tb11027.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY