GB600041A - Improvements in and relating to the production of corrosion-resistant surfaces on copper and copper-alloy surfaces - Google Patents

Abstract

In a process for producing, and an article possessing, a cupriferous surface with increased resistance to corrosion, the cupriferous surface is subjected to the action of an aqueous solution containing chromic acid and zinc ions, between 0.075 and 175 gm. per litre of total chromic acid being dissolved therein, and which solution is saturated with respect to zinc ions, so that any further zinc compound added remains undissolved. In practice the ratio of zinc to chromic acid in the treating solution preferably corresponds to a Zn O:Cr O3 ratio of between 25 : 75 and 35 : 65. Examples are given of the method of producing satisfactory solutions by dissolving flake chromic acid (Cr O3) in water followed by the addition a zinc oxide, hydroxide or carbonate or mixtures thereof until some zinc compound remains undissolved. The treatment may consist of a single dip in a strong solution containing between 8.5 and 175 gm./litre, and preferably between 15 and 90 gm./litre, of Cr O3; or a dip in a strong followed by dipping in a weaker solution containing 0.075 to 15 gm./litre, and preferably 0.8 to 2.5 gm./litre, of Cr O3; or for smoothly polished, dense surfaces a dip in the weaker solution only. Where the two-dip process is employed one of the solutions need not be saturated with respect to zinc ions, and if this applies to the first (stronger) solution a water rinse should be interposed between the dips. The solutions are preferably used hot, between 190 degrees F. and their boiling point, and the treatment may be applied to superficial cupriferous surfaces on ferrous base metals. The treatment also provides a good foundation for a subsequent organic coating of e.g. paint, lacquer or enamel. Spraying or washing with the solution(s) may replace dipping. U.S.A. Specification 2,217,921 is referred to.