Aluminum, Silicon, Carbon Reductant And Mechanism Of The Synthetic Bauxite-based Sialon

This paper studies the process of synthesizing Sialon based on bauxite by aluminum thermal reduction-nitridation, silicon thermal reduction-nitridation and carbonthermal reduction-nitridation methods, using DTA-TG, thermal balance, XRD analysis and SEM with ED AX. The effect of crystal water on synthesization of Sialon and the influnces of the three reduction agents on the reaction processes are also compared.The aluminum thermal reduction-nitridation reactions involved are found to proceed in five stages as follows: (1) Formation of A1N(600-800); (2) Reduction of SiO2 and formation of Si3N4(900-1200癈); (3) Initial formation of P -Sialon(1300-1350癈); (4) Formation of Si2N2O and transitory Sialon phase(1400or so); (5) Ultimate formation of P -Sialon(Z=3) (1450-1500 癈).The ultimate microstructure of P -Sialon crystals are regular short and long column with crystal size about 1 Oum.The silicon thermal reduction-nitridation reactions involved are found to proceed in fourstages as follows: (1) Formation of Si3N4 (900-1200 );(2)Initial formation of Si2N2O andfurther formation of O'-Sialon (1200-1300);(3) Reduction of SiO2 and initial formation ofP-Sialon(l 300-1400 );(4) Ultimate formation of 逽ialon and O'-Sialon (1450-1500).Most of the Sialon crystals formed are whiskers.The carbonthermal reduction-nitridation reactions involved are found to proceed in three stages as follows: (1) Reduction of mullite and cristobalite(1300-1350);(2) Formation of P -Sialon from X-phase as the intermediate product(1400-1450癈);(3) Partially formation of 15R from P -Sialon(1500-1550).The ultimate microstructure of P -Sialon crystals are long column with crystal size about lOum.