Composite Reductant Nitride Research In The Synthesis Of Bauxite-based ¦Â-sialon

The process of synthesizing P-SiAlON based on bauxite by using combined reduction agents C/Si, Al/Si, Al/C and single reductor of C, Si, Al, has been studied. The mass change ratio of the specimens are determined; Phase composition and microstructure of some specimens are examined by XRD, SEM and EDS. P-SiAlON based on bauxite compared with oxided, and the influences of the two additives TiO₂, Fe₂O₃on the reaction process β- SiAlON based on oxided are also compared. The results show:The process of synthesizing bauxite based P-SiAlON by using carbon/silicon reducing agent was studied. The results are compared with those of specimens using Si and C separately as reducing agent. It is found that at 1100-1200°C only Si reacts with N₂ and SiO₂ to form Si₂N₂O; At 1300-1400°C, C takes part in reduction-nitridation with subsequent formation of P-SiAlON; At 1450-1550°C, there is noticeable increase in P-SiAlON formation ,the optimum temperature is 1500°C. The amount of p-SiAlON formed is higher and crystal growth is better than that of single reducing agent.The process of synthesizing bauxite based P-SiAlON by using aluminum/ silicon reducing agent was studied. The results are compared with those of specimens using Al and Si separately as reducing agent. It is found that at 1100 only Al reacts with N₂ and SiO₂ to form AlN and Si; At 1200-1350°C, Si takes part in reduction-nitridation with subsequent formation of P-SiAlON; At 1450-1550°C, there is noticeable increase in P-SiAlON formation, the optimum temperature is 1500°C. The amount of P-SiAlON formed is higher and crystal growth is better than that of single reducing agent.The process of synthesizing bauxite based P-SiAlON by using aluminum/carbon reducing agent was studied. The results are compared with those of specimens using Al and C. It is found that at 1100 only Al reacts with N₂ and SiO₂ to form AlN and Si; at 1200°C Si reacts with N₂ and Si₃N₄; 1300¹400°C, C takes part in reduction-nitridation with subsequent formation of P-SiAlON; At 1450-1550°C, there is noticeable increase in P-SiAlON formation, the optimum temperature is 1500°C. The amount of p-SiAlON formed is not higher and crystal growth is not better than that of single reducing agent. So using combined reduction agents Al/C to synthesize bauxite based p-SiAlON is not ideal.