Preparation of Si₃N₄-SiC multiphase ceramics by nitridation sintering method

The influence of phenolic resin binder on bending strength of green body and phase compositions of nitridation sintered silicon nitride was studied by cold isostatic pressing and nitridation sintering method. With the increase of the phenolic resin, the bending strength of green body also increases and comes to the maximum 23 MPa. Moreover, the green body can be directly mechanically processed. SiC is generated with content ranging from 7.1% to 15.7%. The equiaxed grains of α-Si₃N₄, rodlike crystals of β-Si₃N₄, acic-ular crystals of Si₃N₄, and some little whisker like Si₃N₄ can be observed in SEM photographs. SiC grains are found bonding with Si₃N₄. The generation mechanism is discussed:at 300-600°C, the phenolic resin decomposes to C with residual C rate about 50%; at 1000-1100°C, the residual C begins to react with Si to generate SiC; and after 1100°C, the Si begins to react with N₂ and generate Si₃N₄.