PHYSICAL AND CHEMICAL PECULIARITIES OF FORMATION OF ALUMINIDES OF IV–V GROUPS METALS IN HYDRIDE CYCLE

The traditional methods for production of Ме^IV-V aluminides are laborious, long-lasting and multi-stage. The Laboratory of High-Temperature  Synthesis and Technology of Inorganic Compounds has developed a new highly efficient  method for obtaining alloys and intermetallides of refractory metals, the “hydride cycle” (HC) method. This review presents the results of systematic studies of HC-formation of aluminides in the systems TiH₂–Al, ZrH₂–Al, NbH_1,23–Al, TiH₂–Al–ZrH₂, TiH₂-Al-NbH_1,23. The review describes the influences on this process of such parameters,  as chemical characteristics of hydrides, the ratios of the initial components, phase transformations, etc., and  proposes a mechanism for the HC-formation of aluminides of IV-V groups metals: upon heating of compacted хМеH₂+(1-х)Al→Ме_хAl_1-х+Н₂↑, the hydrogen dissociates from the hydride; in the environment of the liberated hydrogen, the oxide film is removed; a very active metals are formed, which instantly interact with aluminum exothermically  by a solid-phase mechanism without aluminum melting. We have synthesized in HC more than 30 aluminides: single-phase α₂-Ti₃Al, γ-TiAl и TiAl₃; solid solutions of Al in Zr: Zr₃Al, single-phase ZrAl_2, ZrAl₃ and Zr₃AlH_4.49 hydride; single-phase NbAl₃ , Nb₂Al and Nb₃Al, containing about 10% Nb₂Al; Ti_0,35 Zr_0,4Al_0,25; Ti_0,55Zr_0,2Al_0,25; Ti_0,25Al_0,5Nb_0,25; Ti_0,45Al_0,28Nb_0,27, Ti_0,2Zr_0,05Al_0,75; Ti_0,2Zr_0,05Al_0,75, etc. Without preliminary crushing, some aluminides interact with hydrogen in the SHS mode forming reversible hydrides. Based on the obtained results, two concentration triangles for Ti-Al-Zr and Ti-Al-Nb systems were constructed. Compared with existing methods, the synthesis in HC of aluminides of IV and V group metals has significant advantages: relatively low temperatures (~ 1000°C) and short duration (30-60 min) of process; formation in one technological stage, without melting of the original components; environmentally friendly and energy-saving, economically viable, etc. Synthesis of trialuminides occurs at temperatures of 650-670ºC. Aluminides based on Me^IV-V groups are very promising construction materials, they are used in aerospace and ground machine-building, defense industry, chemical and food industry,  electronics, as biocompatible materials in medicine, etc.

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