Thermodynamic properties of solid monoarsenides and monobismuthides of the rare-earth metals

Translated from Poroshkovaya Metallurgiya, No. 11 (347), pp. 37–39, November, 1991.     

Electrophysical properties of fused hexaborides of the alkaline- and rare-earth metals

Powder Metallurgy and Metal Ceramics -     

Gallochalcogenides of the rare-earth metals

A discussion of published data on the structure of gallochalcogenides of the rare-earth metals is followed by an account of an experimental study of the electrical properties of neodymium galloselenide. The electrical resistance and thermo-emf were measured over a range from room temperature to 1100°K. It is shown that neodymium galloselenide is a semiconductor in which the width of the forbidden band and ionization energy of the impurity level are 1.78 and 0.77 eV, respectively. The semiconductor nature of the conductivity of NdGaSe₃ is explained on the basis of the electronic structure of isolated atoms and their ionization potentials. An assumption is made regarding the nature of the chemical bond in chalcogenides of rare-earth metals.Presented at the Fifth All-Union Inter-Institute Seminar of the Physical Properties and Electron Structure of the Transition Metals and Their High-Melting Compounds and Alloys, Kiev, April 5–9, 1966.Translated from Poroshkovaya Metallurgiya, No. 1(49), pp. 99–104, January, 1967.     

Intermetallic compounds of rare-earth metals with aluminum and some of their properties

Conclusions The article reviews literature data on the systems of the rare-earth metals with aluminum, taking into account new results obtained by using high-purity rare-earth elements. The intermetallic compounds in these systems are classified. A table is included, summarizing the crystallographic, as well as some physical and chemical properties of all known intermetallic compounds in these systems.Translated from Poroshkovaya Metallurgiya, No. 8(44), pp. 76–85, August, 1966.     

Reduction of metals from sulfides

Existing notions on reduction of metals from oxides and sulfides are based on realization of dissociative processes associated with the formation of simple substances. Metal sulfides can be considered as compounds of oppositely charged species formed owing to totality of electrostatic and coordination binding in the Me^z+-S^2? system. Reduction of metals from such compounds with the use of donor properties of sulfide sulfur is an electrochemical process with the participation of the electrode pair Me^z+ and S^2? in the mode of internal electrolysis in the system, which provides utilization of elemental sulfur that is formed through chemical reactions. As an electrochemical medium, molten caustic soda is proposed. In its presence, elemental sulfur disproportionates with the preferential accumulation of sulfide and sulfate sulfur. The reaction causes irreversibility of the reduction process.     

Review of the world market of rare-earth metals

On the basis of publications of recent years, the contemporary state of the world market of rare-earth metals is reviewed, periods of its development are considered, and prospects are shown.     

Reaction of rare-earth metals with boron and aluminum

We have used x-ray phase analysis to establish the phase equilibria at 600°C for the systems Gd-Al-B, Tb-Al-B, and Ho-Al-B (the boron-rich sites have not yet been studied). We determined the crystalline structure of the new borides HoAlB₄ and ErAlB₄ (space group Pbam, YCrB₄ type, a=59283(7), b=1.1553(1), c=0.35306(5) mm for HoAlB₄ and a=0.59955(9), b=1.1487(2), c=0.35284(8) nm for ErAlB₄). We synthesized the compound Tm_1?xAl_1?yB₁₄ with MgAlB₁₄ type structure (space group Imma, a=0.5826(2), b=1.0380(2), c=0.8176(2) nm) by the method of crystallization from an aluminum melt.     

Thermal expansion of some sulfides of the transition metals

Summary The coefficients of thermal expansion of sulfides of the transition metals were determined experimentally. The elastic constants, characteristic temperatures, and mean square amplitudes of elastic vibrations of these sulfides were evaluated,     

High-temperature phase transitions in rare-earth metals

The study into the relationship between the laws of structure formation in metallic melts and the properties of collective ion vibrations is continuing. The phase-transition temperatures are found from the Lindemann criterion, where the root-nean-square amplitude of ion vibrations about a center of equilibrium is compared to the properties of the distribution of such centers. In a liquid phase, the vibration amplitude can decrease with increasing temperature.     

Solid-State displacement reactions between selected metals and sulfides

Displacement reactions between sulfides and metals in the solid state are studied and compared with the resultant morphologies previously observed in oxide-metal displacement reactions. Sufficient thermodynamic and diffusion data were available only for the theoretical prediction of product morphology for the Fe-Ni₃S₂ reaction couple. Experiments substantiated the theoretical prediction of an aggregate morphology for this couple at 600°C. The growth of the product zone for the Fe-Ni₃S₂ reaction couple obeyed parabolic kinetics. The experimentally observed morphologies for Co-Ni₃S₂, Fe-Co₄S₃, Mn-Crs, Nb-Cu.₂S, Cr-Cu₂S, Cr-Ni₃S₂, and Mn-Cu₂S reaction couples are also reported and rationalized.