K. Y. Shunyaev

Thermal Properties of CuGa2 Phase in Inert Atmosphere

Thermal decomposition of copper digallide was studied using experimental (thermal analysis) and theoretical (thermodynamic modeling) methods. The temperatures of CuGa2 incongruent melting are in satisfactory agreement between experimental and calculated values. Small differences with the phase diagram can be explained by minor non-stoichiometry of the alloy samples. The experimental studies of thermal diffusivity and thermal expansion of CuGa2 were performed in the temperature range 298-500 K. The heat conductivity coefficient was further calculated using literary data concerning the density and heat capacity of the copper digallide.

The Characteristic of Ores and Concentrates of the Open Society "EVRAZ KGOK"

The results of preliminary experimental researches of possibility of metallurgical processing of ores of Actually Kachkanarsky deposit are presented in the work.

Thin Scandium Layer on Solid Aluminium: Thermodynamic Investigation

Thin scandium-containing layers fabricated by different methods are good systems to investigate some properties of Al-Sc intermetallic compounds (IMC). The electrochemical deposition of a thin scandium layer onto a solid metallic surface leads to complex diffusion processes, especially if the second metal forms a number of IMC with Sc. Here, we used the electromotive force (EMF) method to study thin Al-Sc films in dynamics. Also, the Al-Sc alloy layers were prepared by direct aluminium-scandium interaction. The results of SEM and EDX investigations of these alloys are also presented in this paper. Analogue coatings (like Sc on Ni, Y on Cu, Al on Ni etc.) were also considered in order to discuss the phase sequence formation.

Influence of the Transition to Nanoscaled State on Electrochemical Properties of LaMnO3+δ Oxide

The electrochemical behavior of perovskite type LaMnO3 (LMO) oxides with different mean particle size was studied by voltammetry with the use of a carbon paste electroactive electrode. Three stages of electrochemical reduction were recognized. The first two of them are related to the release of oxygen from the crystal lattice in the range of two side nonstoichiometry of LaMnO3±δ whereas the final stage is conditioned by the decomposition of LaMnO3-δ into new phases. The nature of these phases and their formation mechanisms are different for nano- and microparticles. The utmost size effect appears on cathodic curves recorded from the stationary potential. The effect is not only due to the size factor but also due to the difference in electrochemical properties of nano- and microparticles. While the decomposition of LaMnO3 microparticles proceeds into La2O3 and MnO oxides, the nanoparticles decompose through the intermediate stage of Mn3O4 formation in accordance with the transformation sequence principle.

Effect of Mechanical Activation on the Electrochemical Behavior of MnO2

Electrochemical behaviour of mechanoactivated β-MnO2 powders has been studied by the method of cyclic voltammetry with a carbon-paste electroactive electrode. Mechanical activation was carried out by dry grinding in an AGO-2 planetary ball mill. It was found that the grinding process results in a mechanochemical effect in the surface layer of the oxide particles: Mn (IV) cations are reduced to Mn (III). Voltammetry test detects that mechanical activation of β-MnO2 leads to a new state, which is characteristic for the γ-modification of manganese dioxide (β-MnO2 γ-MnO2).

Slow Crystallization of Al-Sc Alloys: Growth of Spherical Intermetallic Particles

The solidification of binary Al-Sc melts containing small amounts of scandium (< 2 wt.%) have been investigated. We studied concentration profiles in long Al-Sc as cast ingots formed by slow cooling of the liquid alloys. It was found that minor addition of transition metals like Ti can lead to the formation of large (about 10-20 μm) spherical intermetallic particles (Al3Sc containing some amount of isomorphic Ti). These sphere-like particles are forming during the crystallization of liquid solution of Sc in Al (before the precipitation on nanosize spherical particles from the solid solutions). The results of SEM and EDX investigations of these alloys are also presented in this paper.

Physical Properties of Diffusive-Hardening Alloys of Copper with Gallium and Tin

Gallium-based diffusive-hardening solders do not contain lead. These alloys have specific rheological properties. Their synthesis includes, as a rule, mechanical mixing of such initial components as gallium, copper and tin powders [1]. Then the metallic paste undergoes irreversible phase transformations forming a solid alloy with a specific structure. Here, we investigated microstructures of diffusive-hardened Cu-Ga-Sn alloys by SEM and EDX methods. Thermal diffusivity and heat conductivity of alloys mentioned above were studied by the laser flash method. Also differential scanning calorimetry (DSC) experiments were performed to obtain heat properties of the samples.

The Diffusion of Gallium into Copper-Tin Alloy Particles

Properties of diffusive-hardening pastes based on liquid gallium have been investigated. The optimal conditions were found for producing the paste (solder) with best technological characteristics. The liquid-solid ratio, powder alloy composition and dispersity, dust fractions percentage, exposition time and temperature are the main factors which determine the rheological properties of the gallium paste.

MnO-C Interaction – Thermodynamic Modelling of Phase Equilibria

The interaction between manganese(II) oxide and carbon in powder mixtures may give manganese carbides, condensed(c) and gaseous(g) manganese at different temperatures and pressures. The initial assumptions and results of thermodynamic modelling of this interaction in the temperature range 1600-2100 K at the pressures 0.1-1.0 MPa are presented in this paper.

Phase Transitions in Mixed Jahn–Teller Systems with Competitive Interactions

Phase diagrams of mixed crystal systems exhibiting the cooperative Jahn–Teller effect are investigated. The competition of Jahn–Teller interaction with a) the preference energy of cation distribution over nonequivalent sublattices or b) stabilization energy of 3d-ion valence configuration is considered. The developed model enables to explain the nature of equilibrium and metastable states, the variety of phase diagrams and its special features in crystals with the competing interactions.