The preparation of β sialon from Kaolin by carbonitrothermic reduction

The preparation of β-sialon from Turkish kaolin by carbothermic reduction under a nitrogen atmosphere has been described. The product of carbonitrothermic reduction at 1475-1500¶C comprises principally β-sialon and minor amounts of another phase in the SiAl-N-O system known as the 15R phase. The amount of each of these two phases strongly depends on reaction time. The colloidal stability behaviour of the ground carbothermal β-sialon in water was found to depend strongly on the pH. Slip casting of the β-sialon powder from the suspension followed by sintering at 1500 to 1600¶C resulted in compounds with densities ranging from 94 to 99% of the theoretical value. The particle size of the β-sialon influences the densification achieved during sintering. The use of yttria in amounts of 5 and 10% as an additive to β-sialon to obtain higher densities by sintering works well for relatively coarser powder.