Novel synthesis of MoSi 2 and MoSi 2 -Al 2 0 3 ultrafine powders

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.