GB726935A - Improvements in the phosphate coating of metals - Google Patents

Abstract

Phosphate coatings are formed on metal surfaces by the use of a solution of an orthophosphate, other than phosphoric acid alone, which solution contains either no metal or a metal which does not itself enter the coating and at most only small amounts of a metal which does enter the coating, the solution also containing an oxidizing accelerator and one or more phosphates less highly hydrated than the orthophosphate being added to the solution. Orthophosphates of sodium, potassium, magnesium, ammonium or organic bases such as triethanolamine, guanyl urea and pyridine may be used; the accelerator may be a chlorate, nitrite, nitrate, sulphite, hydroxylamine, an oxy-acid of vanadium, chromium or molybdenum, a halogen oxy-acid, m-nitrobenzene sulphonic acid, o-nitrochlorbenzene-p-sulphonic acid, 3-nitrophthalic acid, nitrophenol, m-nitrobenzoic acid, nitrobenzene or m-nitrotoluene or salts of the various acids; and the other phosphate may be a pyrophosphate, a metaphosphate or a polyphosphate. The solution may also comprise surface-active agents such as sulphonates or organic compounds containing nitrogen-bound polyether groups or oxyethylated higher alcohols. After treatment, the surface, which may be of iron, steel, zinc, aluminium or their alloys, may be rinsed and further treated with a dilute solution of chromic, phosphoric or oxalic acid or their salts. Specification 517,049 is referred to.