共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Schmok 《Crystal Research and Technology》1988,23(8):967-972
The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials. 相似文献
2.
Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical... 相似文献
3.
S. S. Batsanov 《Crystallography Reports》2001,46(6):891-897
The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions. 相似文献
4.
M. Szurgot 《Crystal Research and Technology》1991,26(5):555-562
The formulae for absolute Rdisap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity RA/RcritA of the vanishing face A with respect to the critical growth velocity RcritA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in RA/RcritA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal. 相似文献
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6.
V. A. Nepochatenko 《Crystallography Reports》2004,49(5):828-831
Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics. 相似文献
7.
I. Avramov 《Journal of Non》2011,357(22-23):3841-3846
The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts xi of all oxides dissolved in SiO2, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature Tr , at which viscosity is ηr = 1013 [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, li is a product of molar part xi and a specific dimensionless coefficient 0 ≤ ki ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature Tr,SiO2 of pure SiO2. 相似文献
8.
Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi3 existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species. 相似文献
9.
Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented. 相似文献
10.
SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process. 相似文献
11.
V. Pu
lka 《Crystal Research and Technology》1979,14(8):999-1004
The diffraction function expressing the dependence of the intensity of the diffracted X-rays on the angle of diffraction ϱ is derived. On the basis of this equation two methods of measuring the microcrystal size in the direction of the normal line onto the beam of coherently diffracting atom planes are elaborated. Further, the methods for measuring the diffraction line enlargement owing to the experimental conditions are given here. 相似文献
12.
M. Szurgot 《Crystal Research and Technology》1991,26(7):823-831
Growth conditions affect the velocities of disappearance and lifetime of faces of growing crystals. Supersaturation is a factor which causes either an increase or a decrease in velocities of disappearance of faces and their lifetime depending on the mechanism and kinetics of growth of disappearing and adjacent faces. The possible relationships between velocities of disappearance of faces, their lifetime and supersaturation have been derived and discussed. 相似文献
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14.
Crystal chemical characteristics of the α and β modifications of Zn2V2O7 are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn2V2O7 unit cell in the temperature range of 300–600°С, α V =–17.94 × 10–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn2V2O7 is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices. 相似文献
15.
A. V. Markov E. V. Zaitseva V. N. Trushin E. V. Chuprunov 《Crystallography Reports》2013,58(7):1043-1047
We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile. 相似文献
16.
Morphologic and kinetic behaviour of the hill of the (001) face of TGS crystal, generated by unparallel dislocation center of growth under inconstant supersaturation and temperature has been experimentally examined. Some irreversible changes in the shape of the hill top, as a hysteresis in its normal rate of growth is registered. A model, on the base of which a qualitative anylsis of the phenomenon is proposed. 相似文献
17.
A. A. Blistanov B. I. Zadneprovskii M. A. Ivanov V. V. Kochurikhin V. S. Petrakov I. O. Yakimova 《Crystallography Reports》2005,50(2):284-290
Crystals of divalent tungstates are characterized by two main luminescence spectral ranges: a short-wavelength (blue) luminescence band in the range 390–420 nm and a group (often two groups) of longer wavelength (green) bands in the range 480–520 nm. For crystals of calcium, strontium, barium, cadmium, magnesium, zinc, and lead tungstates, it is shown that the wavelength corresponding to the maximum of the blue luminescence band (λmax) correlates with the melting temperature (Tm) of these compounds. The position of the blue luminescence band is the same (in the range 510–530 nm) for crystals with different divalent cations. Annealing in vacuum and electron irradiation decrease the intensity of both blue and green luminescence bands but do not change the ratio of their maximum intensities. This circumstance suggests that vacancies serve as luminescence quenchers to a greater extent rather than facilitate the formation of emission centers responsible for a particular luminescence band. 相似文献
18.
《Progress in Crystal Growth and Characterization》1989,18(3):189-245
This paper describes and discusses the micromorphology of as-grown surfaces of single crystals. After a brief introduction to the methods of observation of surfaces, the mechanism of growth and development of crystals is first outlined. Here the formation of bunches and macrosteps, the relationship between the growth mechanism and the surface entropy factor, and the effect of impurities on the surface morphology are described. Common structures observed on the as-grown surfaces are then explained in relation to growth conditions of the crystals. The following growth structures are described: elementary spirals, macrospirals, hillocks of dislocation and nondislocation origin, interlacing and slip patterns, macrosteps, inclusions, block structures, growth striations and impurity striations. 相似文献
19.
S. N. Smirnov 《Crystallography Reports》2001,46(1):157-160
The role of a scientific library and, in particular, the library of the Institute of Crystallography of the Russian Academy of Sciences, in the development of crystallography has been considered as well as the place of the library of the Institute of Crystallography in the information flows based on the achievements in modern crystallographic research. 相似文献
20.
G. F. Sarafanov 《Crystallography Reports》2004,49(5):816-819
Mechanisms of spatial ordering of dislocations during plastic deformation of crystals are considered. The system of evolution equations, which take into account the effects of elastic and correlated interactions of screw dislocations, is derived. The study is performed with due regard for the dynamics of spatial fluctuations of the dislocation density. 相似文献