Effect of mechanical activation on synthesis of ultrafine Si₃N₄-MoSi₂ in-situ composites

Abstract

Si₃N₄-MoSi₂ in situ composite has been synthesized by reacting powders of molybdenum (Mo) and silicon nitride (Si₃N₄). Mo and Si₃N₄ powders mixture in a molar ratio of 1:3 were ball milled for 0-100 h. The milled and unmilled powder mixtures were reacted at different temperatures between 1000 and 1600 °C in an argon atmosphere. The effect of mechanical activation (MA) induced by milling has been studied through X-ray diffraction (XRD), differential thermal analysis (DTA), and thermo-gravimetric analysis (TGA). No peaks of Mo in the XRD pattern have been observed after 70 h of milling. The crystallite size of the Mo has been found to be the lowest (41 nm) after milling for 30 h. Similarly, a 100 nm lowest size of crystallite of Si₃N₄ was observed after milling for 50 h. DTA and TGA results show that the reaction between Mo and Si₃N₄ enhances with increase in milling time. Milling for 10 h lowers the pyrolysis temperature by 150 °C. Additional milling upto 100 h does not lead to further reduction in the pyrolysis temperature. The intensities of peaks of MoSi₂ in the pyrolysed samples increased with increase in milling time. MoSi₂ particles of size less than 1 μm were observed to be uniformly distributed through out the Si₃N₄ matrix.