1. G. W�tting andG. Ziegler, in Proceedings of an International Symposium on Ceramic Components for Engines, edited by S. Somiya, E. Kanai and K. Ando (KTK Scientific, Tokyo, 1983) p. 412.
2. G. Petzow andP. Greil,ibid.in p. 177.
3. G. W�tting, B. Kanka andG. Petzow, ?Nonoxide Technical and Engineering Ceramics?, edited by S. Hampshire (Elsevier Applied Science, London, 1986) p. 83.
4. O. Abe,Ceram. Int. 16 (1) (1990).
5. D. W. Richerson,Amer. Ceram. Soc. Bull. 5 (1973) 560.