1. K. SUGANUMA, T. OKAMOTO, M. KOIZUMI and M. SHIMADA,Adv. Ceram. Mater. to be published.
2. Idem, Am. Ceram. Soc. Bull. 65 (1986) 1060.
3. L. REED and R. C. McRAE,ibid. 44 (1965) 12.
4. M. G. NICHOLAS and D. A. MORTIMER,Mater. Sci. Technol. 1 (1985) 657.
5. K. MÜLLER and H. REBSH,Silikattechnik 17 (1966) 279.