Gas-Pressure Sintering Map for Silicon Nitride-Based Materials

Abstract

The effect of N₂ gas pressure on the sintering of silicon nitride-based ceramics (α and ß sialon) is examined. When gas pressure is low, reactions occur between Si₃N₄ and oxides and dense compacts are not obtained. Using the gas-pressure sintering method, dense compacts are produced at an elevated N₂ gas pressure. However, N₂ gas pressures higher than 10 MPa result in lower density because high pressure gas inside the closed pores inhibits densification in the final stage of sintering. These results suggest that silicon nitride-based materials should be sintered at an appropriate gas pressure to minimize thermal decomposition and to promote shrinking after pore closure. A gas-pressure sintering map is proposed for sintering silicon nitride-based ceramics under suitable gas pressure and temperature conditions.