Features of the Solid Solution (Mo0.9,Cr0.1)Si2 Formation Depending on the State of Initial Mixture

The regularities of solid state synthesis of the solid solution (Mo0.9,Cr0.1)Si2 in vacuum have been investigated in the temperature range 400-1200℃ depending on the dispersity and energetic state of the initial powders, namely molybdenum, chromium and silicon. The energetic state of the initial mixture was established to be a determining 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 planetary mill with low number of drum revolutions were used, the solid solution formation proceeded owing to diffusion of silicon into metals through successive formation of lower and higher molybdenum-based silicide phases followed by their interaction. Mechanical activation in a planetary mill with high number of drum 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 modifications, were formed with further polymorphic transition of the unstable high temperature hexagonal β-MoSi2 phase into the low temperature tetragonal α-MoSi2 phase. It has been established that temperature of the beginning of interaction decreases by 100℃ as compared with non-activated initial mixtures and temperature of the end of the process depends on the amount of accumulated energy: under low energy mechanical activation the process is complete at 1200℃, while a high energy activation decreases this temperature by 200-400℃ depending on the duration of activation.