1. N. L. Parr, G. F. Mastin and E. R. W. May, ?Special Ceramics? edited by P. Popper (Haywood and Co. Ltd, London, 1960) p. 102.
2. P. L. Pratt, ?Mechanical Properties of Engineering Ceramics? edited by W. W. Kriegel and H. Palmour III (Interscience, New York, 1961) p. 507.
3. H. C. Dunegan, ?Mechanical Properties of Engineering Ceramics? edited by W. W. Kriegel and H. Palmour III (Interscience, New York, 1961) p. 521.
4. P. B. Noakes and P. L. Pratt, ?Special Ceramics 5? edited by P. Popper (British Ceramic Research Association, Stoke-on-Trent, 1972) p. 299.
5. R. F. Coe, R. J. Lumby and M. F. Pawson, ?Special Ceramics 5? edited by P. Popper (British Ceramic Research Association, Stoke-on-Trent, 1972) p. 361.