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

Abstract

Abstract Si 3 N 4 –MoSi 2 in situ composite has been synthesized by reacting powders of molybdenum (Mo) and silicon nitride (Si 3 N 4 ). Mo and Si 3 N 4 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 Si 3 N 4 was observed after milling for 50 h. DTA and TGA results show that the reaction between Mo and Si 3 N 4 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 MoSi 2 in the pyrolysed samples increased with increase in milling time. MoSi 2 particles of size less than 1 μm were observed to be uniformly distributed through out the Si 3 N 4 matrix.