Effect of calcium aluminates content on the formation of Сa-α-SiAlON ceramics obtained by hot-pressing

This study explores a novel method for fabricating Ca-alpha-sialon ceramics using a calcium aluminate oxide eutectic additive. Conventional sintering techniques for Ca-alpha-sialon ceramics employ nitrogen-containing additives to facilitate the Si-N bond substitution mechanism with Al-O and Al-N bonds. In this work, calcium aluminate additives are utilized, leading to the formation of Ca-alpha-sialon ceramics via carbothermal reduction processes and partial nitridation of aluminum oxide. The influence of varying calcium aluminate content (5, 10, 15, 30, and 40 wt%) on the phase composition of Ca-alpha-sialon ceramics, produced by hot pressing at 1650 degrees C in a nitrogen atmosphere, was investigated. Results indicate that increasing the calcium aluminate content leads to the formation of a beta-sialon phase, which subsequently transforms into Ca-alpha-sialon. At 40 wt% calcium aluminate, complete conversion of alpha-Si3N4 to Ca-alpha-sialon is achieved, with significant glassy phase formation at the grain boundaries. The study elucidates the relationship between calcium aluminate content, phase composition, lattice parameters, mechanical properties, oxidation resistance, and thermal expansion of the ceramics.