A stochastic model for solidification II. Application to binary metallic melts

A stochastic model to study the solidifcation process developed in part I is applied to various binary alloys having different values of interaction energies. The results obtained for the time evolution of temperature and concentration, rate of growth and shape of the solid-liquid interface are presented.     

On the interest of synchrotron X-ray imaging for the study of solidification in metallic alloys

Recent developments of more powerful synchrotron sources have led to vast improvements in the performance of X-ray imaging. This is manifested by a continuous increase in the impact of synchrotron experiments in many research areas on materials, in particular solidification science. X-ray imaging has been established as a method of choice for in situ and real-time studies of solidification microstructure formation in metallic alloys, with spatio-temporal resolutions at the scales of relevance. In this article, we present illustrative results of the current capabilities of synchrotron X-ray imaging in this field of research, each of them using different X-ray techniques (radiography, topography and tomography). Those results demonstrate the high potential of these techniques for the investigation of dynamical phenomena in materials processing.     

Investigation of corrosion processes in metallic samples by optical and electrochemical methods

A comparative investigation using simultaneously Michelson optical interferometry and cyclic electrochemical polarization tests to determine the evolution of corrosion processes taking place is presented. As optical monitoring of corrosion in an electrochemical system compound by metallic samples immersed in acid or brine-type aqueous solutions is performed, the consecutive appearance and disappearance of interference patterns formed by reflection from the sample surface as time goes by is observed. This behavior, as well as a brief mutual analysis and discussion of the obtained optical patterns recorded during electrochemical tests and corresponding potentiodynamic curves, is reported here.     

液态金属凝固过程原子团簇结构表征的新方法（英文）

采用分子动力学方法对液态金属钠的凝固过程进行了模拟计算,运用团簇结构表征新方法――团簇类型指数法(CTIM)对凝固过程中的团簇结构进行了识别.为了阐明CTIM在识别团簇结构上的准确性和效率,将其与广为采用的Voronoi多面体方法 (VPM)进行比较.结果表明:当采用CTIM和VPM分别对液态金属钠凝固结构中的原子团簇结构进行表征时,它们所得到的微观结构特征是一致的.非晶态结构中,原子团簇类型的分布呈现明显的区段特征,每一区段都存在一种主要团簇类型,它们分别是二十面体或其缺陷结构.晶体结构中,体系形成以BCC团簇为主体的晶态结构.同时发现,VPM不易区分不同团簇构型之间的细微差别,不同构型的原子团簇可能被归为同种结构类型;而CTIM根据近邻原子之间相对位置关系,直接准确描述原子团簇的构型.不但由CTIM分析获得的凝固体系结构特征与VPM的分析结果一致;而且CTIM抓住了体系微观结构特征的主要方面,简化了团簇结构的表征形式,这在大尺度模拟体系的结构分析中将具有较高效率.     

Chemical behaviour of metallic inclusions in glass melts

Inclusions of all kinds cannot be accepted in glass articles. Most of them are non-metallic stones, silicon spheres, cords, bubbles, and sometimes metallic inclusions. Identification of every appearance is not possible, since body structure and chemical composition do not compare. Laboratory experiments regarding the behaviour of the metals copper, brass and iron and their dissolution mechanisms in glass melts at technological relevant temperatures were analysed. Besides partial oxidation processes, sulphidic species were found. The experiments have been compared with thermodynamic calculations of several reaction mechanisms.     

Investigation of electrotransfer in two-phase metallic alloys

Diffusion, electrotransfer, and electrical conductivity are investigated over the temperature range 1100–1300°C in pure molybdenum, in the intermetallide MoNi, and in Mo-40 at.% Ni. The mass transfer of both components is studied in the last two alloys. The diffusion temperature parameters and the specific electrical resistance are found, and the effective charges of molybdenum and nickel are calculated. Using the experimental data obtained, the degree of ionization of the atoms of the elements investigated is determined for all items. The admissibility of application of the relations of the theory of electrotransfer in heterophase systems, developed earlier by the authors, is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–51, June, 1978.     

Dynamical mechanism of two-phase phenomena in financial markets

Two-phase behavior of the Korean treasury bond (KTB) futures in the Korean exchange market is investigated in this study. To show that the two-phase phenomena are due to heavy-tailed behavior of distribution of price returns, actual data from the KTB futures market with shuffled data and a generated time series are examined according to the Brownian process. In addition, we study the correlation inherent in the KTB futures and its Brownian walk, describing the extent to which the volatility clustering plays a crucial role in equilibrium and nonequilibrium states of financial markets. It is shown that the two-phase behavior essentially results from heavy-tailed behavior of the distribution of price returns. This two-phase behavior does not appear to be relevant to volatility clustering.     

Theory of molecular-kinetic processes in glass melts

Various equations that characterize the molecular mobility in vitrifying liquids and the vitrification process are compared and analyzed. The Williams-Landel-Ferry equation is treated within the framework of the relaxation theory of vitrification, and its relationship with the equations of Bartenev and Shishkin is discussed. The Shishkin equation for the activation energy is derived on the basis of the hole theory of liquids and the concept of free volume. As a result, the empirical constants in the Williams-Landel-Ferry and Shishkin equations take on a simple physical meaning.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 11, pp. 93–101, November, 1968.     

Undercooling and solidification of germanium melts studied by differential scanning calorimeter

~~Undercooling and solidification of germanium melts studied by differential scanning calorimeter~~     

High-precision nuclear magnetic resonance probe suitable for in situ studies of high-temperature metallic melts

High-temperature nuclear magnetic resonance (NMR) has proven to be very useful for detecting the temperature-induced structural evolution and dynamics in melts. However, the sensitivity and precision of high-temperature NMR probes are limited. Here we report a sensitive and stable high-temperature NMR probe based on laser-heating, suitable for in situ studies of metallic melts, which can work stably at the temperature of up to 2000 K. In our design, a well-designed optical path and the use of a water-cooled copper radio-frequency (RF) coil significantly optimize the signal-to-noise ratio (S/NR) at high temperatures. Additionally, a precise temperature controlling system with an error of less than ±1 K has been designed. After temperature calibration, the temperature measurement error is controlled within ±2 K. As a performance testing, ²⁷Al NMR spectra are measured in Zr-based metallic glass-forming liquid in situ. Results show that the S/NR reaches 45 within 90 s even when the sample's temperature is up to 1500 K and that the isothermal signal drift is better than 0.001 ppm per hour. This high-temperature NMR probe can be used to clarify some highly debated issues about metallic liquids, such as glass transition and liquid-liquid transition.     

Study of plasma dynamics and acceleration processes in the high-current discharge by X-ray spectropolarimetry methods

The possibilities of studying the fast process dynamics in dense hot plasma by X-ray spectropolarimetry methods are presented.     

Experimental investigation of magnetodynamic processes in two-phase flows

Power plants for use in investigation of flows of products of combustion of metallized plasma-forming fuels in a combustion chamber, Laval nozzle, and MHD channel and for determining the physical characteristics of plasma are described. The results of experimental investigations and numerical calculations of the combustion of fuel in a combustion chamber and flows of combustion products through gas-dynamic channels were employed in the design of the power plants.Scientific-Research Institute of Applied Mathematics and Mechanics at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 92–100, April, 1993.