1. R.L. Crosby, D.H. Desy, U.S. Bureau of Mines Report 7266, 6, 1 (1969)
2. J.S. Benjamin, The International Nickel Company Inc., US Patent 3, 785 (1974)
3. A.V. Nadkarni, E. Klar, US Patent 3, 714 (1973)
4. S. Boudrahem, Ph.D. thesis, University of Poitiers, 1978