GB1233582A - - Google Patents

Abstract

1,233,582. Anodizing. REYNOLDS METALS CO. July 5, 1968 [July 20, 1967], No.32318/68. Heading C7B. An anodizable metal e.g. Al or its alloy is anodized by passing an electric current preferably D.C. between the metal immersed as anode 22 in an aqueous anodizing electrolyte 21 and a cathode 24 e.g. of Pb or graphite immersed in a non- polarizing electrolyte 25, the electrolytes being separated by at least one cationic permselective membrane 26, e.g. of PVC provided in the walls of at least one membrane cell 23, to prevent deleterious reaction between the anodizing electrolyte 21 and the cathode. For forming a hard coloured anodized oxide coating on Al, the anodizing electrolyte contains a metal ion, e.g. of Fe, Cu, Ni, Co or Mn, and preferably comprises (a) 0À05 to 4À5% M 2 SO 4 , (b) 0À5% to saturation of an aliphatic and hydroxy mono- or di-carboxylic acid, e.g. oxalic, glycolic, lactic, malic, malonic, succinic or maleic acid, and (c) 0À1% to saturation of a metal salt of the acid (b), e.g. ferric oxalate. (a) may be another acid, such as nitric, boric, hydrofluoric, sulphamic or tartaric acid. The non-polarizing electrolyte may be a solution of sulphuric, phosphoric, chromic or oxalic acid, preferably a 4 to 35% H 2 SO 4 solution. The C.D. may range from 12 to 60 A. S. F. The permselective membrane may be a sulphonated crosslinked polymer of styrene or phenol-aldehyde condensation product, polystyrene-divinylbenzene or divinylbenzene-olefinic carboxylic acid forming copolymer, or a condensation polymer of resorcinol dimethyl ether sulphonic acid and formaldehyde.