1. D. P. H. HASSELMAN,J. Amer. Ceram. Soc. 52 (1969) 600.
2. Idem, ibid.53 (1970) 490.
3. M. SHIMADA, K. MATSUSHITA, S. KURATANI, T. OKAMOTO, K. KOIZUMI, K. TSUKUMA and T. TSUKIDATE,J. Amer. Ceram. Soc. to be published.
4. W. W. KRIEGEL and H. POLMOUR, ?Mechanical Properties of Engineering Ceramics? (Interscience Publishers, New York, London, 1961).
5. J. C. GLANDUS and P. BOCH, ?Energy and Ceramics?, Proceeding of the 4th International Meeting on Modern Ceramics Technologies, edited by P. Vincenzini (1979) p. 661.