Controllable Synthesis of High-purity β-SiAlON Powder

The Gibbs free values of different SiAlON were assessed by the thermodynamic quasi-paraboloid rule in Si3N4-AlN-SiO2-Al2O3 system and the thermodynamic parameter for β-SiAlON were explored at 1800K.The synthesis of β-SiAlON based on coal gangue and carbon black by carbonthermal reduction nitridation method,and phase transformation of β-SiAlON powder in various atmospheres(such as air or nitrogen of different purity) were discussed in detail.Thermodynamic analysis reveals that different SiAlON can be synthesized in suitable atmosphere parameter Y(Y=lg(PO2/Pθ)-2/3lg(PN2/Pθ)) at 1800K,and low Y value is beneficial to synthesis of β-SiAlON.When excessive carbon exists in the atmosphere,with the increase of purity(α) of initial nitrogen,the Y value decreases,and the relationship between purity(α) and Y value is Y=2lg[(2-2α)/(2-α)]-2/3lg[α/(2-α)]-15.616.The experiment results shows that the suitable initial parameters based on thermodynamic analysis is highly advantageous in controllable synthesis of high-purity β-SiAlON,the proper initial parameters is that samples,burying in coke,are sintered at 1800K in a flowing nitrogen atmosphere,the purity range of nitrogen is about 0.995-0.999.