Yr. Xu et al., RESIDUAL ALPHA-SI3N4 IN O' CRYSTALS IN CEO2-DOPED O'+BETA' SIALON CERAMICS, Journal of the American Ceramic Society, 77(8), 1994, pp. 2213-2216
The microstructure of a pressureless sintered (1605-degrees-C, 90 min)
O' + beta' SiAlON ceramic with CeO2 doping has been investigated. It
is duplex in nature, consisting of very large, slablike elongated O' g
rains (20-30 mum long), and a continuous matrix of small rodlike beta'
grains (< 1.0 mum in length). Many alpha-Si3N4 inclusions (0.1-0.5 mu
m in size) were found in the large O' grains. CeO2-doping and its high
doping level as well as the high Al2O3 concentration were thought to
be the main reasons for accelerating the reaction between the alpha-Si
3N4 and the Si-Al-O-N liquid to precipitate O'-SiAlON. This caused the
supergrowth of O' grains. The rapid growth of O' crystals isolated th
e remnant alpha-Si3N4 from the reacting liquid, resulting in a delay i
n the alpha --> beta-Si3N4 transformation. The large O' grains and the
alpha-Si3N4 inclusions have a pronounced effect on the strength degra
dation of O' + beta' ceramics.