Effects of starting composition and carbon content on the formation of Ca-α SiAlON powders by carbothermal reduction-nitridation

Ca-α SiAlON powders were prepared at different starting compositions and carbon contents at 1450°C for 2h in N₂ from mixtures of SiO₂, Al₂O₃, CaCO₃ and carbon powders by carbothermal reduction-nitridation. Crystalline phases and particle morphology of the products were investigated. With increasing the x value in nominal Ca-α SiAlON compositions Ca_xSi_12-3xAl _3xO_xN_16-x, the number of small hollow spheres decreased and the size of primary grains consisting of the hollow spheres increased. The addition of carbon powder to more than 1.2 times of the necessary stoichiometric value was required to form Ca-α SiAlON hollow spheres composed of ultrafine grains.