Hot-pressed Si3N4 ceramics containing CaO-Al2O3-AlN modifying additives

We have studied the influence of SHS aluminum nitride content (5-15%) and particle size on the fabrication conditions (hot pressing in a nitrogen atmosphere) of Si3N4-based ceramics containing CaO-Al2O3-AlN sintering aids. The results demonstrate that the reaction of Si3N4 with a eutectic calcium aluminate mixture during liquid-phase sintering leads to the formation of alpha-sialon-based intergranular phases: Ca (m/z) Si12 - (m - n)Al(m + n)O (n) N16 - n . The addition of AlN to starting mixtures contributes to a more complete conversion of the calcium aluminate sintering aid to Ca-alpha-sialon and influences the relationship between alpha-Si3N4 and beta-Si3N4 in the ceramics. We examine the influence of synthesis conditions and the percentages of added calcium aluminates and aluminum nitride on the density, porosity, and bending strength of the ceramics. Thermogravimetric analysis data demonstrates that the Si3N4 + Ca-alpha-sialon composites obtained are stable to oxidation in air up to 1300A degrees C.