GB534852A - Improvements in rendering iron and steel of improved resistance to corrosion - Google Patents

Abstract

534,852. Coating iron and steel. PYRENE CO., Ltd. (Parker-Rust Proof Co.). July 25, 1939, Nos. 21643/39 and 12070/40. [Class 82 (ii)] To improve the resistance of iron and steel to corrosion by the formation of a chromate coating thereon, a bonding film forming part, but only a minute part, of the final coating is first formed on the iron and then a main coating solution, including radicals containing hexavalent chromium is applied over the bonding film and a film of this solution dried, e.g. by heating, on the surface. The main coating solution may also contain orthophosphate radicals. The bonding film may be formed by the chemical surface reaction of a solution with the iron, e.g. by a solution containing arsenic, bismuth, antimony, molybdenum, lead, tin, mercury, cobalt, nickel, cadmium, silver, copper, titanium, thallium, tungsten, vanadium, manganese, strontium, barium or calcium and the solution containing them is prepared by dissolving a nitrate of the metal in water or dissolving an oxide of the metal in acid such as phosphoric, hydrochloric or sulphuric acid, so that some of the acid is left in the free state. An oxidizing agent such as nitric acid or perchlorates, permanganates, sulphates, persulphates, iodates, periodates, bromates, peroxides, quinone and ceric salts or a mixture of such agents may be added. The second solution may consist of any solution containing hexavalent chromium, e.g. that described in Specification 447,704 and may contain a wetting agent such as sodium lauryl sulphate and sulphonated higher alcohols. In an example the surface of the metal is cleaned and then treated for 30 seconds with a heated solution containing 2,000 c.c. of water, 5 grams of arsenic pentoxide, 50 grams of 75 per cent. orthophosphoric acid and 5 grams sodium chlorate to form the bonding film. After treating with the main coating solution the coated article is then baked at 500‹F. The bonding film may be produced by etching with acids or by applying a very thin film of metal electrolytically. Specifications 362,956 and 530,006 also are referred to.