Si3N4 composite ceramic preparation with kerf loss silicon powder from photovoltaic industry by molten salt assisted nitriding method

In this paper, Si ₃ N ₄ composite ceramic were synthesized with kerf loss silicon waste powder as the raw material by molten salt assisted nitridation method. Na ₃ AlF ₆ molten salt was introduced into the system and the effects of Si-salt ratio, nitridation temperature on the nitriding product were investigated. These results indicated that the addition of Na ₃ AlF ₆ promotes the conversion of waste silicon to Si ₂ N ₂ O, and 90.7% of Si ₂ N ₂ O phase was obtained with the Si-salt ratio of 1:1.5 at 1350℃. The increase in temperature causes the main phase of the product changes from Si ₂ N ₂ O to β-Si ₃ N ₄ , which is due to the decomposition of Si ₂ N ₂ O and the α→β phase transition of Si ₃ N ₄ . And the content of β-Si ₃ N ₄ phase reached 72.9% with the Si-salt ratio of 1:0.75 at 1450℃. The formation mechanism was analyzed combined with the in-situ nitriding process.