GB1036400A - Surface treatment of an oxide coated metal article - Google Patents

Abstract

A method of improving the corrosion resistance of oxidized metal surfaces characterized by the steps of (A) immersing the oxide coated metal in a bath of a soluble amphipathic material, i.e. a material having molecules which are highly polar and water solubility-enhancing in one portion of the molecule and are non-polar and insolubility-enhancing in another, and (B) passing an electric current at a potential of at least 2 volts through said bath between an inert cathode and said oxide coated metal as an anode, said bath being maintained at a temperature of 50-150 DEG C. Amphipathic materials which may be used include saturated or unsaturated water soluble fatty acid salts, e.g. fatty carboxylates; anionic surfactants, e.g. alkyl, aryl or alkylaryl sulphonates, phosphonates &c. and cationic surfactants, e.g. fatty amines and fatty aminium salts; the preferred materials being sodium stearate, sodium oleate, sodium laurate, potassium ricinoleate and sodium lauroyl sarcosinate. The thickness of the oxide coating should be at least 0.01 mil thick, the electrolyte is preferably at a temperature of 70 DEG -100 DEG C., the voltage 70-120 V and time of electrolysis from 30 seconds to 60 minutes. Prior to this treatment the oxide coating may be treated with water at a temperature within 10 DEG F. of its boiling point, with a metal hydroxide solution of pH at least 8 and temperature 0-100 DEG C., or an acidic solution having a pH of 3 or less. The bath may contain the amphipathic material in a proportion from 0.0001% to saturation, and preferably from 0.01 to 1.0%.