Synthesis of silicon nitride by conventional and microwave carbothermal reduction and nitridation of rice hulls

•Conventional and microwave carbothermal reduction was used to synthesize Si3N4.•Digested rice hulls were pyrolised and reacted under N2 flow.•The particles size of microwave Si3N4 was smaller than the conventional ones.•The phases obtained in the conventional powder were the same of microwave powder.•The reaction time was reduced about 90% using microwave energy.

Rice hulls were used as raw material to produce Si3N4 by conventional and microwave carbothermal reduction and nitridation. The precursor was made by the digestion of rice hulls with 12 M HNO3, followed by pyrolisis of digested hulls to reduce the organic carbon. The precursor was then pelletized and reacted in conventional and microwave furnaces. The intimate of SiO2 and carbon mixture favored the complete formation of Si3N4 in conventional reaction. However, SiC residual phase was present in the product of microwave reaction probably owing to the rapid temperature increasing of the reaction, caused by the thermal runaway effect of alumina pipe reactor.

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