CS252300B1 - Bath for semi-products' gold pre-plating,especially with surface of nickel or its alloys - Google Patents

Abstract

The bath contains gold in the form of a complex potassium dicyanate, substances with a reducing effect selected from the group comprising organic acids, for example formic acid, free organic an acid such as citric acid and a base such as sodium hydroxide, for example adjusting the pH and the metal of the group comprising iron, nickel and cobalt in the same form complex such as gold or salt inorganic salts such as cobalt sulfate.

Description

Bath for galvanic pre-gilding of semi-finished products, especially with a surface of nickel or its alloys

The bath comprises gold in the form of a potassium dicyanolate complex, a reducing agent selected from the group consisting of organic acids such as formic acid, a free organic acid such as citric acid and a base such as sodium hydroxide for pH adjustment and a metal selected from iron, nickel and cobalt in the form of the same complex as gold or in the form of a salt of an inorganic salt, for example cobalt sulfate.

252 300

- 1 252 300

The invention relates to a bath for the electroplating of preforms, in particular with a surface of nickel or its alloys, based on potassium dicyanolate.

The baths used for pre-gilding the blanks, especially those with a nickel layer, require the nickel layer to be perfectly active, otherwise the gold layer which is peeling off badly will peel off and the product will be destroyed. This phenomenon occurs especially when using mass plating technology in drums, where the immersion of the drum in the bath does not cause immediate electrical contact with all individual components.

The techniques used to gild nickel or its alloys to date are aimed at destroying the oxide layer, which impairs the adhesion of the electroplated coatings. Typically, cathodic activation is used in a strongly acid chloride nickel plating bath - about 0.1 µm active nickel thickness - and by eliminating a 3 to 4 µm nickel interlayer which only provides a suitable substrate for conventional pre-gold plating in a weakly acid cyanide gold bath.

Achieving the active surface for workpieces with an intermediate nickel layer or a nickel alloy - kovar, etc. permaloy. - ensures bath according to the invention whose principle consists in that, _in '-1 that it contains 2 to 4 gl dikyanozlatnanu potassium 3-15 gl ¹ of a reducing agent selected from the group consisting of organic acids, e.g. formic acid, aldehydes, e.g. acetaldehyde, alcohols, e.g. methanol, aromatic amines, e.g. aniline sulfate, from 30 to 70 gl ^-1 organic acids, e.g. citric acid, alkaline hydro2

252 300 xid, for example sodium hydroxide, in an amount such that the resulting pH of the bath is in the range of 4.5 to 6.5, a metal from the group comprising iron, nickel and cobalt, in the same complex as gold or in the form of an inorganic salt of acid, in an amount of 0.04 to 0.1 g / ^l , for example cobalt sulfate, and up to 1 liter of distilled water.

The reducing substances contained in the bath keep the surface of the nickel and its alloys permanently active and at the same time reduce the trivalent gold formed by the electrochemical oxidation at the anode to monovalent, thereby increasing the cathode current yields. The bath contains organic acids and alkali hydroxides to increase the reducing effect and maintain the desired pH. To reduce the porosity and improve the structure of the first gold layer, a metal from the group comprising cobalt, nickel and iron in the form of a complex or inorganic acid salt is added to the bath.

The bath operates at temperatures of 10 to 50 ° C, the optimum bath temperature is 20 to 30 ° G, the pH of the bath is in the range of 5 to 6. The current density is used up to 2A / dm

The bath according to the invention makes it possible to achieve high-quality gold coatings without the need for cathodic activation of the gilded surface and the formation of a nickel intermediate layer, in a much more economical manner than hitherto known.

The invention is further described in more detail by way of examples of a possible specific embodiment thereof.

Example 1 Potassium dicyanolate 3 g / l citric acid 50 g / l formic acid 80% 5 g / l sodium hydroxide to pH 5.5 cobalt sulfate 0.050 g / l

252 300 temperature 20 ° C, 1 A / dm ² , pre-gilt time 30 s.

The components are gradually added to the water while stirring and after dissolution and treatment of the pE, the bath is ready for use.

Example 2 Potassium dicyanolate 3 g / l tartaric acid 50 g / l formaldehyde 40% 10 g / l potassium hydroxide at pH 6.0 nickel carbonate 0.05 g / l temperature 20 ° C, = 1 A / dm ² , pre-plating time 30 p.

The bath was prepared as in Example 1.

Example 3 Potassium dicyanolate 3 g / l malic acid 50 g / l scalic acid 10 g / l sodium hydroxide to pH 5.0 ferrous chloride 0.050 g / l temperature 20 ° C, = 1.5 A / dm ² , pre-plating time 60 with.

The baths are particularly suitable for pre-gilding semi-finished products made of nickel and its alloys or coated with a galvanically deposited layer of nickel for the electrotechnical and jewelery industry.

Claims (1)

? S E D Μ S Τ OF THE INVENTION 252 300 A bath for the electroplating of semi-finished products, in particular with a surface of nickel or its alloys, based on potassium dicyanolate, characterized in that it contains from 2 to 4 g of potassium dicyanolate, from 3 to 15 g of reducing agents selected from organic acids, for example formic acid, aldehydes, for example acetaldehyde, alcohols, for example methanol, aromatic amines, for example aniline sulphate, from 30 to 70 g / l of organic acids, for example citric acid, alkaline hydroxide, for example sodium hydroxide, make the resulting. The pH of the bath was in the range of 4.5 to 6.5, a metal of iron, nickel and cobalt, in the same complex as gold or in the form of an inorganic acid salt, in an amount of 0.04 to 0.1 g. Such as cobalt sulfate, and up to 1 liter of distilled water.