1. J. Wuellner and B. Sweo, J. Am. Ceram. Soc.,38, No. 11, 404 (1955).
2. J. Kreuter and H. Hoens, Mitt VDEfa,12, No. 12, 81 (1964).
3. K. P. Azarov and V. E. Gorbatenko, Tr. Novocherkasskovo Politekhnicheskovo Inst.,154, p. 63 (1963).
4. V. F. Gorbatenko et al., Fiz. Khim. Mekh. Mater.,10, No. 2, 33 (1974).
5. H. Poschman, Sprechsaal,102, No. 12, 52 (1969).