Kinetics of dissolution of BaF2 crystals

Kinetics of dissolution of BaF₂ crystals in aqueous solutions of HNO₃ and HCl acids have been studied for the different acid concentrations in the temperature interval 20–100°C. It is established that this process is diffusion controlled. Activation energy is constant, but pre-exponential factor is dependent on the concentration of the acid.     

The influence of time dependence of temperature on the kinetics of nucleation

In this work the influence of time dependence of temperature on kinetic processes during nucleation on a simple model is studied. The nucleation rate and the average effective radius of nuclei R is counted. It is proved that in the case of oscillating temperature the nucleation rate also oscillates and the rate of growth of radius R is directly proportional to frequency of temperature change.     

Identifiability of dislocation structures of strongly distorted crystals

Diffraction analysis of polycrystals is adapted to the state of their dislocation structure. A structure with small dislocation loops (the martensite-transformation structure) is revealed clearly. For large dislocation loops (the plastic-deformation structure), distinguishability of loop sizes is restricted significantly.     

Investigation of the Microstructure of Crystals Surfaces by the Method of Self-decoration during Ion Bombardment

A method is developed for self-decoration with ion bombardment by which the surface structure of crystal samples is investigated. The existing surface structure of the objects, as well as the additionally developed structure after prolonged ion bombardment are visualized by this method. When using scanning electron microscopy the method allows multiple investigation of the sample or of one and the same parts of it respectively. The mechanism of the method is revealed by the results obtained in the performed experiments. It is proved that the crystal surface and its decoration depend on the peculiarities of the crystal structure and on the conditions of bombardment. By varying the conditions of ion bombardment the sensitivity of the method is considerably changed.     

Study of liquid crystals at the institute of crystallography

The history of studying liquid crystal at the Shubnikov Institute of Crystallography is briefly reviewed. The scientific results of researchers from the institute (starting from the 1960s and leading to the formation of a new field of science: physics of liquid crystals) are presented. In particular, it is shown how the physics of electro-hydrodynamic instability was developed in the 1970s. The origin of the physics of photonic crystals is considered. The discovery of the ferroelectric properties of ultrathin films of polar molecules is described. A breakthrough in the molecular theory of ferroelectricity in liquid crystals in the new century is discussed. The entire abundance of liquid-crystalline phases and processes occurring in them is estimated. An analysis of the participation of researchers from the Institute of Crystallography in the development of liquid-crystal science demonstrates their valuable contribution, which offers perspectives of new studies in this field.     

Fundamental laws of fracture region of solids

The present paper reports that the deformation is statistically symmetric even in the fracture region of solids. The major factor in the fracture region of brittle solids is the creation of new surfaces. On the basis of the creation of new surfaces, four fundamental laws are derived for the fracture region of brittle solids. These laws are: (i) New surfaces are created only after a particular strain of the crystal. (ii) For the smaller values of compressive strain, the area of newly created surfaces is directly proportional to the square of the strain. (iii) The proportionality constant between the area of the newly created surfaces and the square of strain may be termed as fracture constant. Mathematically the fracture constant is the area of newly created surface for unit compressive strain of the crystal. (iv) For larger values of the compressive strain, the logarithm of newly created surfaces is directly proportional to the strain. The experimental verification of the laws of fracture region of solids are discussed. The value of fracture constant of certain solids are estimated and their significance is discussed.     

Study of a Surface Layer of Calomel Monocrystals by the Method of Plastmatic Etching

The method of plasma (ionic) etching provides information on both the degree of damage and the real structure of a treated surface of a cleavage crystallographic plane (110). The altered surface structure of this plane, which is due to cutting, grinding and polishing, is a cause of a rapid loss of calomel at the beginning of the etching process. The minimum loss rate is directly proportional to the thickness of the damaged surface. The ensuring rapid loss of calomel is due to an increased ruggedness of the surface. The ionic etching of calomel on the crystallographic plane (110) proceeds in six phases which are documented in photographs. The method of ionic etching is promissing for a high-quality treatment of surfaces of calomel acousto-optical functional elements designed for connections with ultrasound transducers.     

The calculation of critical size of carbon clusters in ferrite

The formation of carbon clusters in ferrite is investigated by the simulation of random motion of carbon particles in a cubic primitive model lattice at different annealing temperatures. All computer runs are repeated to average the results. An interaction potential is assumed between the particles precipitated in the formed cluster and the particles in the matrix. Additionally a decay of the cluster is allowed. A cluster of critical size is formed if the probability of decay is lower than the precipitation rate. The critical size calculated depends on the annealing temperature as the results show unambigously.     

稀土元素对人造金刚石冲击韧性的影响

探讨了含稀土合金粉末对合成金刚石的影响.采用加入少量稀土的NiFe-C作为原料,构成"NiFe-RE-C"粉末材料,再对该粉末一体化芯坯进行活化处理.在超高压、高温的条件下,经一定的工艺流程合成了高品级金刚石.采用该方法的显著特点是提高了金刚石的粗粒度百分比,且生产出的金刚石样品质量高,具有很好的冲击韧性.     

Calculation of volume fraction of phase growing by a diffusion-type law

The problem of determining the volume fraction of a phase is considered for the case where the rate of nucleus growth is a decreasing function of its radius. The solution is obtained within the framework of the geometrical-probabilistic method suggested earlier. The procedure of successive approximations is described, which allows one to determine the volume fraction of a phase with the required accuracy. The errors arising in the calculation of the volume fraction of a phase from the Kolmogorov formula are estimated analytically. As an example of numerical estimates, the case of the diffusion growth mechanism is considered. It is shown that in the three-dimensional space, this error lies within 0.01 irrespective of the initial parameters of the problem.     

Influence of defect-matrix modulus effect on elastic interaction of point defects

An attempt is made to take into account the surface influence upon the mechanical energy of point defects and volume defects in an isotropic elastic solid. In addition the defect-matrix modulus effect is also considered which is usually neglected. A theorem is investigated refering to the sign of interaction energy between defect and surface. An axisymmetric finite element program (FEM) is applied to carry out numerical calculations. The application of this method to probelms in structural physics (microphysics of solids) seems to be very useful.     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

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.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

Controlled growth of filamentary crystals and fabrication of single-crystal whisker probes

The growth of filamentary crystals (whiskers) on a single-crystal substrate through the vapour-liquid-solid mechanism is described. The possibility of fabricating oriented systems of whiskers on the basis of this mechanism of crystal growth is noted. A phenomenon that is important for nanotechnology is noted: the existence of a critical diameter of whiskers, below which they are not formed. The phenomenon of radial periodic instability, which is characteristic of nanowhiskers, is described and the ways of its elimination are shown. The possibility of transforming whiskers into single-crystal tips and the growth of crystalline diamond particles at their apices are noted as important for practice. Possible applications of systems of whiskers and tips are described briefly. Particular attention is paid to the latest direction in whisker technology—fabrication of single-crystal whisker probes for atomic force microscopy.     

L-天门冬氨酸对三水碳酸镁晶体合成的影响研究

依据仿生合成的原理,选择无水MgCl2和无水Na2CO3作为反应原料,通过L-天门冬氨酸和五种无机表面活性剂分别对晶体生长进行调控,应用XRD、SEM对晶体的物相组成以及形貌结构进行表征.试验结果表明当表面活性剂为L-天门冬氨酸时,晶体生长效果最佳.又通过以L-天门冬氨酸添加量和体系pH值为参数变量进行研究,结果表明L-天门冬氨酸质量分数为0.15;,体系pH为9.5为最佳条件,有毫米级束状三水碳酸镁晶体的生成,并对L-天门冬氨酸在仿生合成三水碳酸镁过程中的作用机理进行了初步探讨.     

Application of Riemann geometry to structures of nano- and macrocrystals

The possibility of simulating the structure of real nanomaterials in a Riemann elliptic space is discussed. It is shown that the experimentally obtained parameters of nanomaterials are in good agreement with the simulation patterns. A conclusion is drawn that it is not expedient to isolate nanocrystals into a peculiar group in comparison with polycrystals and single crystals.     

Investigation of the formation and growth processes of silicon carbide monocrystals

The formation and growth processes of SiC monocrystals from vapour phase by sublimation method have been investigated. It is shown that the peaks of the evaporation and growth whiskers are the centres of SiC monocrystals formation. One of the mechanisms of development of the whisker into SiC platelet is established. It is shown that on the naturally mirror like crystal face either the edge of the crystal or the screw dislocation, situated on the crystal edge, is the source of the steps. On the stepped crystal face the root of the crystal is the source of the steps.