Novel synthesis of MoSi2 and MoSi2-Al203 ultrafine powders

Abstract

Molybdenum disilicide (MoSi2) is a promising high temperature material with a high melting point (2032°C), low density (6.24 Mg m-3 ), excellent high temperature oxidation resistance (up to about 1900°C), and metal like thermal and electrical conductivities. For structural applications, the formation of composites can be benejicial. Alumina (Al2O3) has a thermal expansion coefficient close to that of MoSi2 in a wide temperature range from 200°C to 1400°C. Improvement in elevated temperature strength has been reported by the formation of a composite between MoSi2 and A1203. However, the brittle nature of MoSi2 based materials at medium to low temperatures remains an obstacle for their applications. One possible solution is to develop microstructures with ultrajine grains so that ductility can be improved through the grain boundary sliding mechanism. The present work gives preliminary results related to the synthesis ofultrajine MoSi2-Al203 composite powders. The MoSi2 powders (0.1–4 μm) were produced by an electric arc discharge process under varying voltage and capacitance. Three powder generating mechanisms have been identified. The influence of processing parameters (voltage, capacitance, and energy input) on the powder characteristics is discussed. Finally, the synthesis of MoSi2-A1203 composite powders by coating individual MoSi2 particles with an alumina gel through a sol-gel process is also demonstrated.