GB447704A - Improvements in or relating to the rust-proofing of ferrous articles - Google Patents

Abstract

Wetting-agents, e.g. sulphonated lauryl, myristyl, or oleyl alcohol, or the condensation products of naphthalene-b -sulphonic acid with alcohols having 3 or more carbon atoms, are added to solutions of phosphoric acid and chromic acid, chromic anhydride, or a soluble chromate or dichromate for use in the rustproofing of ferrous articles.ALSO:A ferrous article is rust-proofed by coating it by spraying, brushing, or dipping with an aqueous solution of phosphoric acid and chromic acid, chromic anhydride, or a soluble chromate or dichromate, the concentration of phosphoric acid being at least 10 per cent. When a chromate or dichromate is employed the concentration is equivalent to at least 25 parts of sodium dichromate dihydrate per 100 parts of phosphoric acid and when chromic acid or chromic anhydride is used the concentration is equivalent to at least 33 parts of chromic anhydride per 100 parts of phosphoric acid. The upper limit of the concentration of chromium compound is determined by the fact that the solution must contain some free phosphoric acid. After treating with the solution the article is dried, preferably at a temperature between 120 and 200 DEG C. The preferred solution contains from 10-20 per cent of phosphoric acid and from 10-15 per cent of sodium dichromate. A wetting agent such as sulphonated lauryl, myristyl, or oleyl alcohol, or the condensation products of naphthalene-b -sulphonic acid with alcohols having 3 or more carbon atoms may be added to the solutions. To prevent streaking there may be added to the solution an inert colloidal substance, for example 5-20 per cent of bentonite, clay, or colloidal silica. A stiff gel, which may be applied with a cloth, can be obtained by adding liquid sodium silicate to the solution. After drying, the surface is brushed or washed and may subsequently be painted. Specification 398,180 is referred to.