| 摘要 |
Prior to plating a metallic surface is electrolytically oxidized in an aqueous bath containing at least one compound of one or more plating metals to be deposited and a reducing agent, whereafter the surface is chemically or electrolytically plated. Preferably the metallic surface is connected in the electrical circuit before immersion in the bath and oxidation is effected with A.C., D.C., or pulsating D.C. to provide a coating of less than 20m thickness. The oxidation treatment may be employed prior to plating with copper, silver, gold, zinc, cadmium, chromium or nickel, especially on readily oxidizable metals such as aluminium, beryllium, iron, magnesium, titanium, uranium, zirconium or their alloys. The bath may contain simple or complex salts of the metal to be deposited and as reducing agent one or more sulphites, thiosulphites, hyposulphites, arsenites or hypophosphites or lower valency salts of a multivalent metal, e.g. ferrous, titanous, cuprous, or stannous salts, or alcohols, aldehydes, hydrazine or hydroxylamine may be used. The electrolytic oxidation may be effected in the same bath as the subsequent plating or in a similar bath of lower pH. Typically an aluminium base alloy was polished, degreased in trichlorethylene, cathodically degreased in an aqueous solution of sodium phosphate and sodium silicate, neutralized with nitric acid, rinsed, and immersed as anode in an aqueous bath containing per litre 23 gms crystalline nickel sluphate, 24 gms sodium hypophosphite, 27 gms lactic acid, and 20 gms sodium succinate, the pH being adjusted to 4.7 with sulphuric acid or sodium hydroxide, to produce an oxide coating of thickness 0.8m . After switching off, the article remained in the bath at 96-98 DEG C. for 1 hour whereby a nickel layer 22m thick was deposited. An aluminium article after degreasing with trichlorethylene, and chemical brightening in a bath containing phosphoric acid, nitric acid, and copper nitrate at 95 DEG C. followed by rinsing, was anodically oxidized in a nickel hypophosphite bath composed as above at 95 DEG C. but of pH 1. Other pure aluminium articles, after trichlorethylene degreasing, etching in hot caustic soda followed by a neutralizing nitric acid dip and rinsing, were anodically oxidized in aqueous baths containing per litre 23 gms crystallized nickel sulphate, 27 gms lactic acid, 20 gms sodium succinate, and 9 gms formaldehyde or 10 gms pure ethyl alcohol or 56 gms neutral sodium sulphate crystals. Chemical plating of nickel to a thickness of 22m was in each case effected as set out above for the aluminium alloy.
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