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2. D. L. King,Metals 2 (1967) 33.
3. US Patent 2.825.108 (R. B. Pond) (1958).
4. US Patent 3.362.803 (Secretary of Defence, Fed. Rep. Germany) (1968).
5. G. Manfr� andD. Vianello, Italian Patent 930.409 (Montedison S.p.A.) (1972).