Synthesis of Si3N4 powder with tunable α/β-Si3N4 content from waste silica fume using carbothermal reduction nitridation

•Si3N4 powder was synthesized from silica fume by carbothermal reduction nitridation.•Synthesis of Si3N4 was successfully achieved at temperatures as low as 1400 °C.•α/β-Si3N4 relative contents were tailored by adjusting temperature and carbon addition.

Silicon nitride (Si3N4) powder with tunable α/β-Si3N4 relative contents was synthesized from waste silica fume using carbothermal reduction nitridation (CRN) at a relatively low temperature range of 1400–1500 °C. The effects of the carbon source, CRN temperature and raw materials ratio (Carbon-to-Silica fume) on phase assembly and micro-morphology of the products were investigated. Fabrication of α-Si3N4/β-Si3N4 from waste silica fume by CRN was achieved at temperatures as low as 1400 °C. Carbon black was found to be more suitable than coke and graphite for use as the reductant. Elevated temperature was beneficial for the formation of β-Si3N4, whilst excessive carbon black promoted the formation of α-Si3N4. Thus, the α-Si3N4/β-Si3N4 relative contents could be effectively tailored by adjusting the CRN temperature and carbon concentration of the initial mixtures. In addition, the bi-modal crystals of the whiskers and the short columns strongly influenced the morphologies of the product.

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