GB1155865A - Stripping Nickel from Metal Substrates - Google Patents

Abstract

1,155,865. Ni stripping solution. PERNIX ENTHONE. July 1, 1966 [July 1, 1965], No. 29702/66. Headings C7D and C7E. Nickel is stripped from metallic bases (e.g. steel, copper or brass using an aqueous solution consisting of (1) 30 - 12 g/l of a nitro substituted, mononuclear carboxylic aromatic compound with at least one NO 2 <SP>1</SP> group and a water solubilizing group (e.g. - COOH - SO 3 H or salts thereof) attached to the benzene ring, (2) 45 - 135 g/l (expressed as free acid) of one or more of the tri-basic carboxylic acids of the formula and water soluble salts thereof (wherein R 1 is -CH 2 - or - CHOH - and R 2 is - CH - or - COH-) the dicarboxylic acids of the formula HOOC - (CH 2 )n - COOH and water soluble salts thereof (wherein n is an integer from 1 - 4) and the α - hydroxy mono- or dicarboxylic acids of the formula R 1 - (R 2 )n - CHOH COOH and water soluble salts thereof (wherein R 1 is -H or -COOH, R 2 is -CH 2 - or -CHOH- and n is 0, 1, 2, 3 or 4. (3) an ammonium salt of the above acids or ammonium carbonate in an amount sufficient to maintain a pH of 6À8 up to, but below, the pH when the Ni ions start to be complexed by NH 3 instead of by the carboxylic acid, as evidenced by a change in the bath colour from green to blue and (4) 0À075 - 3À75 g/l of this compound as an inhibitor, which will yield S containing ions with S in the - 2 oxidation state in the solution, the pH thereof being in the range set out above. The solution may also contain a wetting agent (e. g. an alkaryl sulphonate and a supplementary inhibitor (e.g. a borate) may be present when the base is a steel. Preferable compounds from the above groups are;- (1) sodium meta nitrobenzoate or sodium meta nitrobenzene sulphonate, (2) adipic citric, gluconic, glycollic, lactic, malic, succinic or tartaric acids, and (4) thiourea, mercapto-benzothiazole, ammonium thiosulphate or ammonium thiocyanate.