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2. T. E. Tietz and J. W. Wilson: 'Behaviour and properties of refractory metals'; 1965, Stanford, Cal., Stanford University Press.
3. C. A. Hampel (ed.): 'The encyclopedia of the chemical elements', 2 edn;1968,New York, Reinhold.
4. C. A. Hampel (ed.): 'Rare metals handbook', 2 edn;1961, London, Reinhold.
5. A. N. Zelikman, O. E. Krein, and G. V. Samsonov: 'Metallurgy of rare metals'; 1966, Jerusalem, Israel Program for Scientific Translations.