Combustion Synthesis and Sintering of β-Sialon Ceramics (z=2)
Mohamed SHAHIEN, Mohamed RADWAN, Soshu KIRIHARA, Yoshinari MIYAMOTO and Toshitaka SAKURAI
Abstract:Single-phase (β-SiAlON (Si4Al2O2N6, z=2) powder has been prepared by the combustion synthesis method. The raw materials (Si, Al and SiO2 ) were combusted with different ratios of (β-SiAlON (z=1) diluent (0, 10, 20, 30, 40, 50wt%) in 1MPa of N2 pressure. Without diluent, the reaction temperature was very high (>2000ºC and the product contained metal Si residue besides (β-SiAlON product. Both the reaction temperature and amount of residual Si decreased gradually with the increase of diluent content up to 50wt%. At 50wt% dilution, the combustion temperature was 1859ºC and the XRD analysis showed complete conversion to pure (β-SiAlON (z=2). The individual peaks of (β-SiAlON (z=1) diluent were also detected in the XRD patterns and disappeared after using the product itself as a diluent five time repeats of combustion at which single-phase (β-SiAlON (z=2) was produced. The sinterability of the best synthesized powder was further studied by spark plasma sintering (SPS) with 5wt% Y2O3 as a sintering aid. High densification (∼97.3%) was obtained after sintering at 1600ºC for 5 min under 30MPa pressure with heating and cooling rates of 100ºC/min. The Vickers hardness and fracture toughness of the sintered SiAlON were 14.8GPa and 4.4MPam1/2, respectively. Key Words:β-sialon, z value, SHS, Combustion synthesis, SPS.