Phosphating metals with polyphosphate solns - of cations which do not form layers, pref. ammonium, pref. by spray-processes

摘要

Metals are phosphated with aq. solns. of polyphosphates having monovalent cations which do not form layers, pref. NH4 polyphosphates. Polyphosphates may have formula MIn+2(PnO3n+1) or MIn(H2PnO3n+1) (where n 1,000,000). Degree of polymerisation (n) is pref. 10-300 (100-250). Even, dense layers can be obtd. immersion, but solns. are pref. sprayed and, more pref. applied as a steam jet or a high-press. jet phosphating soln. Thin, sprayed layers are esp. useful as primers for lacquers. Jet-spraying is useful for large objects, e.g. buses. Phosphating layers adhere well. Sprayed layers can be thinner, adhere solidly and are elastic. Salt spray corrosion tests showed surfaces to resist corrosion by 500 hrs. more than surfaces phosphated with orthophosphates.