Features of the Solid Solution (Mo<SUB>0</SUB><SUB>.</SUB><SUB>9</SUB>,Cr<SUB>0</SUB><SUB>.</SUB><SUB>1</SUB>)Si<SUB>2</SUB> Formation Depending on the State of Initial Mixture

Abstract

The regularities of solid state synthesis of the solid solution (Mo 0.9 ,Cr 0.1 )Si 2 in vacuum have been investigated in the temperature range 400-1200℃ depending on the dispersity and energetic state of the init ial powders, name ly mo lybdenum, chro miu m and silicon. The energetic state of the in itial mixture was established to be a determin ing factor which affects the principal features of solid state interaction whereas an increase in dispersity only influences the temperature of the interaction start. When non-activated initial mixtures and ones mechanically activated in a p lanetary mill with lo w number of dru m revolutions were used, the solid solution formation proceeded owing to diffusion of silicon into meta ls through successive formation of lo wer and higher molybdenum-based silicide phases followed by their interaction. Mechanical activation in a planetary mill with high number of dru m revolutions was accompanied by not only decrease in particle size but also changes in the energetic state of the reaction mixture, which resulted in changing the regularities of the solid solution formation. Herein solid solutions on the basis of two higher molybdenum silicide phases, tetra-and hexagonal mod ifications, were formed with further poly morphic transition of the unstable high temperature hexagonal β-MoSi 2 phase into the lo w temperature tetragonal α-MoSi 2 phase. It has been established that temperature of the beginning of interaction decreases by 100℃ as compared with non-activated initial mixtures and temperature o f the end of the process depends on the amount of accu mu lated energy: under low energy mechanical activation the process is co mplete at 1200℃, while a h igh energy activation decreases this temperature by 200-400℃ depending on the duration of activation.