摘要:

AbstractSynthetic crystals of cinnabar have been grown in a special oven. We have obtained specimens about 3 × 3 × 4 mm3in size and of average crystalline qualit

ISSN:0023-4753    

DOI:10.1002/crat.19790140102

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractA zeolite of P type with a molar ratio SiO2: Al2O3of about 6 was obtained on laboratory and on enlarged scale, by synthesis carried out at 100°C in Na2OK2OSiO2Al2O3H2O system, without complexing agents. It was found that the products depend not only on the chemical composition of hydrogel but also on the kinetic factors such as: the material of the reactor wall, the amount of substrates taken for crystallization and stiring. It was found that the stability of zeolites increases in the order: L

ISSN:0023-4753    

DOI:10.1002/crat.19790140103

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe crystallisation kinetics of strontium tungstate from unstirred saturated solutions in sodium tungstate melts was studied by continuous cooling from initial crystallisation temperaturesT0= 1000° to 800°C to room temperature at cooling ratesRT= 0.67° to 3.3°C min−1. The main crystal growth was diffusion rate‐controlled; the final crystal growth was rate‐controlled by the development rate of excess solute concentration. The estimated diffusion rate constant (kD) values increased with cooling rates and initial crystallisation temperatures. They are higher than the rate constants for diffusion‐controlled growth of calcium tungstate from sodium tungstate melts, but very much smaller than those for strontium tungstate from lithium chl

ISSN:0023-4753    

DOI:10.1002/crat.19790140104

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe combined effects of crystal growth conditions and impurity (Sb, P, B, Ga) concentration on low‐angle boundary (LAB) formation in silicon single crystals growing by Czochralski technique was investigated. The dependence of LAB formation frequency and LAB parameters on crystal growth conditions and impurity content was found. Impurity effects on LAB formation become apparent at concentrations of about 1018cm−3. – All impurity investigated decreases the probability of LAB formation, the acceptor impurity influence is stronger. At B concentration exceeding 2 · 1019cm−3LAB formation does not occur. – Results are interpreted in terms of scheme of LAB formation in thermal stress field of growing crystal. To explain observed impurity effects assumptions about dislocation drag and about raising of critical stresses for dislocation generation with dopin

ISSN:0023-4753    

DOI:10.1002/crat.19790140105

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractDas 1.1′‐Bis‐[phenylglyoxyloyl]‐ferrocen (PGF) kristallisiert in der monoklinen RaumgruppeP21/cmit den Gitterkonstantena= 7,338 Å,b= 16,872 Å,c= 8,046 Å, β = 87,0°. Das PGF gehört zur Klasse der Metall‐π‐Komplexverbindungen. Mit dem Eisen im Symmetriezentrum sind die beiden Schweratomliganden zentrosymmetrisch zu einem Symmetriezentrum sind die beiden Schweratomliganden zentrosymmetrisch zueinander. Die zwei dem Eisen koordinierten Cyclopentadienylringe sind sandwichartig in der gestaffelten Konformation angeordnet. Der senkrechte Abstand ihrer mittleren Ebenen beträgt 3,32 Å. Es gibt in einem einzelnen Phenylglyoxyloyl‐Molekül eine aufgeweitete Csp2–Csp2‐Bindung (1,528 Å). Um diese Bindung sind die beiden ebenen Bauteile des Moleküls gedreht. Diese beiden ebenen Bauteile bestehen einerseits aus dem Kohlenstoff‐5‐Ring und einer C  O‐Gruppe und andererseits aus dem Kohlenstoff‐6‐Ring und einer C  O‐Gruppe. Der Dihedralwinkel beträgt 62,5°. Die erwähnte Bindungsaufweitung wird durch Coulumbabstoßung partiell geladener Atomzentren interpretiert. Die Packung der Mole

ISSN:0023-4753    

DOI:10.1002/crat.19790140106

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe limits of neodymium substitution for yttrium in (Y, Nd)Al3(BO3)4crystals in preparation from solutions in molten potassium trimolybdate have been studied. The maximum neodymium concentration in the crystals was 72 at.%, this corresponding to the ratio Nd:Y = 1 in the solution. When this ratio exceeds unity, only potassium‐neodymium molybdate is formed. The distribution coefficient for neodymium is greater than unity and decreases both with the increasing Nd/Y ratio in the melt and with decreasing growth rate of the crystals. The unit cell parameters change in the series YAl3(BO3)4NdAl3(BO3)4in a non‐steady manner, this indicating that the structure is inclined to disord

ISSN:0023-4753    

DOI:10.1002/crat.19790140107

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractA report is given on the quantum‐mechanical relations in the calculation of heats of fusion for ionic crystals. By correlating the heats of fusion of the respective silver halides (AgCl, AgBr, and AgI) and the alkali nitrates (e.g. NaNO3) with the frequency of the longitudinal optical phonons of the respective crystals, Planck's constant was found to be the proportionality constant. In the alkali halides, apart from the long range interaction, the energy for the formation of vacancies must also be taken into consideration. The calculated heats of fusion agree well with the experimental values given in the literature, deviations being found only in some alkali halide

ISSN:0023-4753    

DOI:10.1002/crat.19790140108

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractAn investigation of the etching behaviour of cleaved octahedral faces of calcium fluoride crystals in sulphuric acid of different concentrations and at various temperatures is carried out. It is observed that the morphology of dislocation etch pits depends on the temperature and concentration of the acid. With an increase in the acid concentration, growth of whiskers, elongated platelets, hexagonal and dice‐shaped elevations, spherulites and sheaves is observed. Temperature of the etchant also has an effect on their formation. By X‐ray diffraction techniques, the compounds forming the whiskers and elongated platelets, and hexagonal and dice‐shaped features are identified as CaSO4· 2 H2O and CaSO4, respectively. The mechanism of the growth of CaSO4· 2 H2O and CaSO4and the change in the morphology of selective etch pit are di

ISSN:0023-4753    

DOI:10.1002/crat.19790140109

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractCleavages of undoped, doped and natural magnesium orthosilicate crystals have been simultaneously etched in concentrated hydrochloric acid solution. The lateral and normal velocities of the growth of pits were then measured at different temperatures for the varieties of crystals. The time dependence of the growth of pit dimensions is found to be linear, while the temperature dependence of the growth of pits is found to be exponential, viz. V =Aexp (−E/kT). The dissolution parameters, e. g. the activation energy (E) and the pre‐exponential factor (A) for dissolution along the surface and along the dislocation lines have been computed. It is observed that: (1) the activation energy (E1) of dissolution along [001] direction is found to be greater than the activation energy (Eb) along [100] direction, irrespective of whether the crystals are doped, undoped or natural, and (2) the doping of the crystal with manganese has lowered down the activation energy (Ed) to such an extent that it is less thanE1andEb. The implications are discus

ISSN:0023-4753    

DOI:10.1002/crat.19790140110

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractAn attachment for scanning microscopes was developed in order to study the deformation, crack, and fracture behaviour of carbon materials during their electron optical observation. Thus the simultaneous registration of electron microscope images, stress‐strain‐curves and acoustic emission rates at different load regimes is possible. The combination of the mentioned methods allows a correlation between the macroscopic material behaviour and the microscopic processes taking place in the material under load. From the submitted experimental results it can be concluded that the fracture toughness of graphitic materials rises with a growing part of lamellar structure and with grain coarsen

ISSN:0023-4753    

DOI:10.1002/crat.19790140111

出版商:WILEY‐VCH Verlag    

年代:1979

数据来源: WILEY