1. Kirk -Othmer: Encyclopaedia of Chemical Technology,1998
2. Ullmann, Encyclopaedia of Industrial Chemistry, 5th ed., vol. A27, 1995, pp. 581–613.
3. Ullmann: Encyclopaedia of Industrial Chemistry, 5th ed., vol. A22, 1993, pp. 399–430.
4. J. Heveling, E. Armbruster, W. Siegrist, WO 9,422,824 A11994.10.13 (1994), to Lonza AG, Switzerland.