Sinterability of Silicon Nitride Powder Produced by the CRN Process

Abstract

In the present work, laboratory experiments were carried out on the sintering of silicone nitride powder without any sintering additives. Silicone nitride powder was produced at own laboratory conditions by carbothermal reduction-nitriding of silica of which was presented elsewhere. It consists of mainly -Si3N4 (83%) and -Si3N4 (17%) phases with a small amount of minor constituents. Before compaction procedure, the powder was ball milled for 2 h and then 2 gr. of the sample was compacted uniaxially at a pressure of 25 MPa. The green compact was placed into furnace in a graphite crucible. The sintering process was carried out in a programmable muffle furnace at 1700 °C and held for 1 h. with a 20 °C/min. heating rate. The sintered compacts were analyzed using X-ray, SEM, SEM-EDS techniques. The results showed that the formation of liquid phase can accelerate the densification of the compact. The densification of the pure SIALON can be increased by adding of sintering aids that accelerates the formation of liquid phases in the sample. The densified sialons give better hardness and thermal properties of the sample. It was well demonstrated that for the densification of sialons large amount of liquid phase forming oxides are needed to add to initial composition. It is also suggested that there is linear relationships between densification and amount of liquid phase formed in the compact.