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

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 deg 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 deg 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 V Lm were observed to be uniformly distributed through out the Si3N4 matrix.