Synthesis of Si₃N₄–MoSi₂ in situ composite from mechanically activated (Mo+Si₃N₄) powders

Abstract

Mo and Si₃N₄ powder mixtures in the molar ratio of 1:3 were mechanically activated by high-energy ball milling for 0–100 h. No MoSi₂ formation was observed during milling. DTA and TGA results showed that the reaction between Mo and Si₃N₄ enhanced with increase in milling time. The milled powder mixtures were reacted at different temperatures between 1000 and 1400°C for the synthesis of Si₃N₄–MoSi₂ in situ composite. Complete conversion of Mo in 10–100 h milled sample into MoSi₂ has been observed after pyrolysis at 1400°C for 1 h. In the unmilled (0 h) sample lower silicide of Mo i.e. Mo₅Si₃ has been detected. In the mechanically activated samples, after 10 h of milling, no Mo₅Si₃ formed after reaction at 1400°C for 1 h. The intensities of peaks of MoSi₂ in the pyrolysed samples increased with increase in milling time. In the pyrolysed sample both nano- and sub-micron size MoSi₂ particles were observed to be uniformly distributed through out the Si₃N₄ matrix.