Of Fe <sub> 2 </ Sub> The O <sub> 3 </ Sub> And Tio <sub> 2 </ Sub> And Other Impurities In The Bauxite-based Sialon Transformation Process Changes And Effect

Investigations on the variation and effects of Fe2O3 and TiO2 during the synthesis process of Sialon based on bauxite, using carbon, aluminium and silicon as reducers, have been carried out. The action mechanism of the two addition agents during the synthesis process of Sialon is studied by the weight variation before and after reaction, XRD, SEM and EDS analysis. The reduction-nitridation rule of TiO2 with different reducer and the oxidation resistance, hydration resistance of TiN and TiN-Sialon are also researched.The results show that Fe2O3 and TiO2 have positive effect on synthesis process of Sialon based on bauxite using carbon, aluminium and silicon as reducer, and Fe2O3 is better than T1O2. Fe2O3 and TiO2 have significant influence on synthesis process of Sialon especially during 1100℃~1300℃ while using aluminium and silicon as reducer. The appropriate additions of Fe2O3 is 2-4wt%, and TiO2 is 4% or so.After reduction-nitridation, most of Fe2O3 were turned into ferro and ferrous oxide with spherical shape except 0.4% Fe2O3 solutionizing in Sialon crystal. The action mechanism of Fe2O3 is mass transport by liquid phase during synthesis process of Sialon. While some of TiO2 solid-solutionizes in Sialon crystal and the other changes into TiN and TiC0.3N0.7. The action mechanism of TiO2 during synthesis process of Sialon is formation of solid solution which activates crystal.In view of Sialon crystal structure, there exists differences by using different reducers, which relatives to the reaction mechanism. The -Sialon crystals formed from carbonthermal reduction - nitridation are short column which is transformed from short columnar mullite with small ratio of length and diameter. The microstructure of -Sialon crystals with Fe2O3 addition have uniform and fully crystallized with crystal size about 1 Sum at 1550℃; By contrast, the crystal size of ?Sialon with TiO2 addition is about lOum with fine crystals about lum dispersed in them. The P -Sialon crystals formed from aluminum thermal reduction-nitridation and silicon thermal reduction-nitridation are long column with large ratio of length and diameter, which are transformed from long columnar Si3N4 granular.TiO2 is reduced by carbon, silicon and aluminum under NI atmosphere. Using aluminum as reduce agent, TiN phase appears at 1100 and the nitridation react is almost completed at 1350. While using carbon as reduce agent, TiN phase appear at 1400 and at 1500 the ultimate phases are TiN and SiO2. TiN and 3 -Sialon can be formed at 1350 vising aluminum and silicon together as reduce agent. It shows that the temperature of reduce reaction using aluminum is lower than using silicon. The most microstructure of TiN is fine irregular granular with crystal size about 2um. Some are fully crystallized with regular cubic shape.By DTA-TG, TiN powder begins to oxidize at about 500 and reacts violently at about 7000, which accompanies with weight increasing quickly. While TiN and 0 -Sialon powder also begins to oxidize at about 500 and react violently at 1100*0. Both TiN and Sialon have better hydration resistance property at room temperature.