1. I. D. Walton, Ceramic Age,76, No. 2, 33 (1960); No. 3, 23 (1960).
2. I. D. Walton, Ceramic Age,77, No. 5, 52 (1961); No. 7, 38?42 (1961).
3. A. E. Williams, Ceramics,16, No. 192, 22 (1965).
4. I. E. Nishanova, et al., in: Highly Refractory Materials [in Russian], Izd-vo Metallurgiya (1966), p. 82.
5. R. Ya. Popil'skii and I. E. Nishanova, Tr. Mosk. Khim.-Tekhnol. Inst., No. 50, 195 (1966).