Quaternary aminomethyl phosphonates as scale inhibitors

A process of inhibiting scale which comprises treating an aqueous system with scale inhibiting amounts of a quaternary aminophosphonate having the general formula ##STR41## where Z is alkylene, alkyl, alkenyl, aryl or aralkyl, R.sub.2 and R.sub.3 are alkyl, alkenyl, aryl, or aralkyl, R.sub.4 and R.sub.5 are hydrogen or alkyl, R.sub.6 is alkyl having 1 to 4 carbon atoms, a is 1 or 2 and b is 1 or 2, with the proviso that when Z is alkylene, a and b are 2 and when Z is alkyl, alkenyl, aryl or aralkyl a and b are 1, with the further proviso that Z and R.sub.2 may be joined to form a cyclic group and X is an anion.