Effect of oxide additives on catalysis and microstructure of RBSN using low-purity silicon powder as raw materials

The three kind of oxides such as 3Y-ZrO₂, Fe₂O ₃ and MgO were used as catalyst in reaction bonded silicon nitride (RBSN) with low-purity silicon powder as raw materials. The oxides can strongly promoted the nitridation ratio of RBSN, and the catalysis effects of these oxides for RBSN were investigated. After 4h nitridation, the degree of nitridation increased from 43% to 96% by adding 10wt% of 3Y-ZrO₂ additive comparing with the sample without additive, and the catalystic effects of Fe₂O₃ and MgO were slightly less than 3Y-ZrO ₂ additive. XRD patterns revealed that the main phases of the reaction products were α-Si₃N₄, β-Si ₃N₄ and Si-N-O intermediation. SEM micrographs show that the hexagonal columnar β-Si₃N₄ separated from acicular α-Si₃N₄.