PREPARATION OF SINGLE-PHASE LITHIUM ALPHA-SIALONS

Lithium alpha-sialon ceramics of composition MxSi12-(m+n) Al(m+n)OnN16 -n, where 0.5 less than or equal to x less than or equal to 2.0, have been prepared by hot pressing and pressureless sintering at temperatur es between 1450 and 1750 degrees C with different packing powders. The Li alpha-sialon single phase legion has been determined at 1750 degre es C, Sor 0.25 less than or equal to m less than or equal to 2.0 and 0 .55 less than or equal to n less than or equal to 2.5, and the reactio n mechanisms and densification processes during the sintering of mixtu res of Si3N4, AIN, Li2O, and SiO2 studied. Li2O first reacts with oxid es on the surface of the nitride powders to form a Li containing silic ate liquid at low temperature, alpha-Si3N4 dissolves in this liquid an d precipitates a beta-LiSiON phase.(1) With increasing temperature, Li alpha-sialon is formed at the expense of beta-LiSiON, alpha-Si3N4, an d AlN. Lithium containing packing powder-plays an important role in re tarding the volatilisation of Li to prepare high yields of Li alpha-si alon. The unit cell dimensions of Li alpha-sialon in the single phase legion can be expressed by the regression equations: a (Angstrom) = 7. 790 + 0.0142m + 0.00733n; c (Angstrom) = 5.650 + 0.00777m + 0.00847n. By testing the significance Of m and n, it was found that iz has the m ore significant effect on a, whereas n has the more significant effect on c at the 0.05 significance more significant effect level. (C) 1998 The Institute of Materials.