β-Sialon/Ti(C,N) composites were prepared using low and middle grade bauxite and ilmenite as raw material,while coke as reducing agent in high purity nitrogen atmosphere through carbothermal reducrion-nitridation(CRN).The main phases of low and middle grade bauxite are kaolinire(Al2O3•2SiO2•2H2O) and (Al2O3•H2O)2 and ilmenite mainly contain ilmenite(FeTiO3) and rutile(TiO2).The reaction products of bauxite are the β-Sialon(Z=3,Si3Al3O3N5) while those of ilmenite are TiC and Fe.The results showed that the main phases are β-Sialon,Ti(C,N),Al2O3 and Fe when the reaction temperature is at 1400°C holding for 4 hours(10wt% ilmenite and 90wt% bauxite as raw material).However,β-Sialon decomposes into 21R at 1450°C and into 15R and AlN at 1500°C.So 1400°C is selected as the proper temperature to synthesize β-Sialon/Ti(C,N) composites.At 1400°C,the β-Sialon crystals with the largest quantity grow well and show long column in shape.With the increase of the reacrion temperature β-Sialon begin to decompose,the β-Sialon crystals change to short columnar,with the number decreasing quickly.

In this study, β-Sialon/Al2O3/TiN diphase powder was synthesized using low-grade bauxite and rutile via carbothermal reduction-nitridation. The phase transitions of low-grade bauxite and rutile in the carbothermal reduction and nitridation process were analyzed by XRD, SEM and EDS. The effects of different reaction parameters such as reaction temperature, rutile addition on the phase composition and microstructure of products were analyzed. The results showed that β-Sialon/Al2O3/TiN powder was prepared using low-grade bauxite and rutile as raw materials and coke as reducing agent by carbothermal reduction-nitridation reaction in flowing nitrogen atmosphere of 0.03 MPa at 1350-1375 °C, for 4 h.

CaAl12O19-Al2O3 composite ceramics were synthesized by in situ solid state reaction using CaCO3 and industrial α-Al2O3 powders. The effects of sintering temperature and ratio of CA6 (CaAl12O19) content on phases and microstructure of the final composite ceramics were studied by XRD and SEM. The result showed that sheet-like CA6 appeared in the materials when sintering temperature was higher than 1400°C and grew up with the increased of the sintering temperature. The optimum sintering temperature was 1600°C, when the sample containing 20wt% CA6 was sintered at 1600°C, the bulk density was 3.21g/cm3, the apparent porosity achieved 9.94% and the bending strength gained 149.88MPa. With the increasing of CA6 content in the final composite ceramics, the bulk density and the bending strength increased firstly and then decreased. The lowest apparent porosity 1.42%, a density of 3.60g/cm3 and the highest bending strength of 265.10MPa were achieved for the sample containing 10wt% CA6 sintered at 1600°C.

Sialon powder was synthesized using low grade bauxite as raw materials by carbothermal reduction-nitridation reaction. The influence of synthesizing temperatures (1300°C, 1350°C, 1400°C, 1450°C, 1500°C and 1550°C) on the phases of the final products was studied by XRD technique. β-Sialon (Z=3) formed at 1350°C and decreased when the temperature was higher than 1450°C. The optimizing reaction temperature for preparing Sialon was 1450°C. The Al2O3-SiC/Sialon composite refractories were prepared at 200°C, 400°C and 600°C for 24h with white corundum, brown corundum, SiC, Sialon powders prepared at 1450°C and calcium aluminate cement. The bulk density, apparent porosity, water absorption and bending strength of the Al2O3-SiC/Sialon composite refractories at room temperature were studied. The results show that the bulk density decreased and then increased with the enhancing of the temperature and reached the highest value of 2.43g/cm3 at 200°C. The apparent porosity and water absorption reached the lowest values of 26.68% and 10.99% at 200°C respectively. The bending strength decreased as the temperature increased, reached the highest value of 0.73MPa at 200°C.