1. Morganite Ltd, British Patent 1326 736 (1969).
2. Airforce, US Patent 3 671 411 (1972).
3. Courtaulds Ltd, British Patent 2 204 156 (1971).
4. Monsanto Research Corporation, St. Louis, US Patent 3 627 570.
5. J. Cziollek and E. Fitzer, International Carbon Conference, Bordeaux, France (1984) pp. 166, 242.