GB963128A - Improvements in or relating to the formation of chemical conversion coating upon metal surfaces - Google Patents

Abstract

Iron and steel surfaces are phosphated with aqueous acidic alkali metal (to include ammonium mono-hydrogen- and ammonium dihydrogen-) phosphate solutions containing nitrite ion (NO2-) and an amine compound of general formula HNR1R2; where R1, R2 the same or not, each being a saturated straight or branched alkyl or o -hydroxyalykyl group having 2-4 carbon atoms: when the amine concentration ranges from 0.3-1.0 gms./litre the <FORM:0963128/C6-C7/1> and when the amine exceeds 1.0 gm./litre [NO2-] ranges from 0.3/amine m.w. X 46 to 10.0 gms./ litre. The pH of the solutions ranges from 4.0-5.8, preferably 4.5-5.7. The temperature is at least 120 DEG F. (49 DEG C.), the operating range being 120-150 DEG F. (49-66 DEG C.) and preferably 130-145 DEG F. (57-63 DEG C.). The amines comprise diethyl amine, di-2-ethanolamine, di-i-propanolamine, di-butylamine, di-i-propylamine and di-butanol-amines. Coating time varies between 30 seconds and 5 minutes, preferably 1-3 minutes. Concentration of the nitrite ion varies directly with respect to concentration of the amine compound up to 1.0 gm./litre of the latter as prescribed by the above formula. For amine contents in excess of 1.0 gm./litre the nitrite ion concentration may rise to a maximum of 10 gms./litre. 30 gms./litre or more of amine may be used as determined only by solubility considerations but in practice quantities are limited to 1.0 gm./litre. The nitrite ion may be introduced as a salt of alkali or alkaline earth metals, preferably NaNO2. Although at least 0.3 gm./litre of amine compound must be incorporated in the solutions, it is preferred to use 0.5 gm./litre of amine as the practical minimum concentration due to drag-out losses. A wetting agent may be incorporated.