Formation of MoSi₂–Si₃N₄/SiC by Reacting Molybdenum with Silicon Nitride

Abstract

The possibility of formation of dense composites of MoSi₂–Si₃N₄/MoSi₂–SiC has been studied by reacting loose powders and compacts of (Mo + Si₃N₄). Two compositions of powder mixtures (Mo + Si₃N₄, 3Mo + 2Si₃N₄) with and without excess Si₃N₄are reacted at different temperatures (1200–1480°C) in a carbon resistance furnace and under nitrogen. MoSi₂has formed as the major phase after reaction at all temperatures. In the powder sample of (Mo + Si₃N₄), MoSi₂MoSi₂–Si₃N₄and MoSi₂–SiC composites have formed at 1300°C and 1432°C, respectively. In the compacted (Mo + Si₃N₄), an MoSi₂–Si₃N₄composite has formed at 1400°C. The excess Si₃N₄in the compact has been found to decompose to form elemental Si after reaction at 1453°C and 1480°C. Formation of SiC whiskers from the elemental Si is also observed in the compacts sintered at 1480°C. In the (3Mo + 2Si₃N₄) system with no excess Si₃N₄, lower silicides of Mo (i.e., Mo₅Si₃and Mo₃Si) are formed at all temperatures. Neither Si nor SiC has been formed in the (3Mo + 2Si₃N₄) system.

Key Words:

• Molybdenum silicides
• Silicon nitride
• Silicon carbide
• Composites
• Sintering

7.0 Acknowledgments

Authors thankfully acknowledge the financial support from the Defence Research and Development Organisation, Ministry of Defence, New Delhi, to carry out this study. They are also grateful to the Director, DMRL, Hyderabad, for his constant encouragement.