Effect of composition and processing conditions on the formation of Y and Er-SiAlON b and I_w phase glass-ceramics

MSiAlON glasses were produced by melting appropriate powder mixtures under nitrogen at 1715 °C using a cation ratio composition of M:Si:Al = 3.45:3:2 (M= Y, Er) with varying nitrogen contents (N=5, 8, 14, 15 e/o). Glass-ceramics were obtained by heat treatment of the glasses under nitrogen atmosphere for 10 hours in the range 1050-1150°C. Parent glasses and the resulting glass-ceramics were characterised by X-ray diffraction (XRD). Two different powder processing routes, using alcohol or water media respectively were compared. The preparation route showed no differences in the nature of crystalline phases formed. However, properties measured on the parent glasses prepared using water media are shown to be slightly poorer than those obtained using alcohol. Low nitrogen content (5-8 e/o N) favours the crystallisation of I_w-phase over B-phase whereas B-phase is formed easily at higher nitrogen content (14-15 e/o N).