Method for electrodeposition of bronzes

Abstract

A method for electrodeposition of bronzes, with which the substrate to be coated is plated in an acid electrolyte that contains at least tin and copper ions, an alkylsulfonic acid and a wetting agent, and the preparation of such an electrolyte.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part from U.S. app. Ser. No. ______ entitled METHOD FOR ELECTRODEPOSITION OF BRONZES filed Apr. 11, 2005, the entire disclosure of which is explicitly incorporated by reference.FIELD OF THE INVENTION [0002] This invention concerns a method for electrodeposition of bronzes, with which the substrate to be coated is plated in an acid electrolyte that contains at least tin and copper ions, an alkylsulfonic acid and a wetting agent, and the preparation of such an electrolyte. BACKGROUND OF THE INVENTION [0003] Methods for deposition of tin and tin alloys on the basis of various types of electrolytes are known from the prior art and are already widely used in practice. Methods for deposition of tin and / or tin alloys from cyanide electrolytes are very common. Such electrolytes, however, are highly toxic, which makes their use problematic from the environmental standpoint, so that for some years there has b...

AI Technical Summary

Benefits of technology

[0072] (56) 3,3′-thiodipropanol represented by HO—CH2CH2CH2—S—CH2CH2CH2—OH. In the above-listed structural formulae, Ph represents a phenyl group.

[0073] As already mentioned above, the method in accordance with the invention is characterized in particular by the special composition of the electrolyte. It contains essentially tin and copper ions, an alkylsulfonic acid and an aromatic nonionic wetting agent. In addition, stabilizers and / or complexing agents, anionic and / or nonionic, aliphatic and / or substituted dithioglycol wetting agents, oxidation inhibitors, brighteners, and other metal salts can optionally be contained in the electrolyte.

[0074] The metals that are primarily added to the electrolyte for deposition of bronzes in accordance with the invention—tin and copper—can first and foremost be in the form of salts of alkylsulfonic acids, preferably as methanesulfonates, or as salts of mineral acids, preferably as sulfates. Tin methanesulfonate is especially preferably used as tin salt in the electrolyte preferably in an amount of 5-195 g / L of electrolyte, preferably 11-175 g / L of electrolyte. This corresponds to a use of 2-75 g / L, preferably 4-57 g / L divalent tin ions. Copper methanesulfonate is especially preferably used in the electrolyte as the copper salt, which is advantageously added to the electrolyte in an amount of 8-280 g / L of electrolyte, preferably 16-260 g / L of electrolyte. This corresponds to the use of 2-70 g / L, preferably 4-65 g / L divalent copper ions.

[0075] Since the deposition is clearly higher in an acid environment, an acid, preferably a mineral and / or an alkylsulfonic acid, is added to the electrolyte in amounts of 140-382 g / L of electrolyte, preferably 175-245 g / L of electrolyte. The use of methanesulfonic acid turned out to be especially advantageous, since for one thing this produces advantageous solubility of metal salts and for another, because of its acid strength, it produces or facilitates the adjustment of the pH needed for the process. In addition, methanesulfonic acid has the advantageous property of contributing considerably to the stability of the bath.

[0076] In accordance with an additional characteristic of the invention at least one additional metal and / or chloride is added to the electrolyte. Advantageously, the metals are in the form of their soluble salts. In particular, the addition of zinc and / or bismuth has a considerable effect on the properties of the deposited coatings. The metals zinc and / or bismuth added to the electrolyte can namely be in the form of salts of alkylsulfonic acids, preferably as methanesulfonates or as salts of mineral acids, preferably as sulfates. Zinc sulfate is especially preferably uses in the electrolytes as zinc salt, and is advantageously added in an amount of 0-25 g / L of electrolyte, preferably 15-20 g / L of electrolyte. Bismuth methane sulfate is especially preferably used in the electrolyte as bismuth salt and is advantageously added to the electrolyte in an amount of 0-5 g / L of electrolyte, preferably 0.05-0.2 g / L of electrolyte.

[0077] In addition, various additives, for example stabilizers and / or complexing agents, oxidation inhibitors and brighteners, that are usually used in acid electrolytes for deposition of tin alloys can be added to the electrolyte.

Problems solved by technology

Such electrolytes, however, are highly toxic, which makes their use problematic from the environmental standpoint, so that for some years there has been a push to develop cyanide-free electrolytes, for example electrolytes based on pyrophosphates or oxalates, which operate in a pH region of 5-9.

However, such methods have both economic and technical disadvantages, of which the relatively slow deposition rates may be mentioned here.

However, such methods have their limits in the deposition of tin-copper alloys with high copper contents, such as the so-called “true” bronzes, which have a copper content of at least 10%.

However, in this form tin can no longer be electrolytically deposited in an acid and thus is withdrawn from the process, which leads to uneven deposition of the two metals and to a decrease of the deposition rate.

In addition, oxidation to tetravalent tin leads to increased sludge formation, which can prevent stable operation and long lifetime of the acid electrolyte.

Moreover, because of such contaminated of a firmly bonding and pore-free coating is no longer guaranteed.

Because of such technical process disadvantages, there is currently no large area of use for electrolytically deposited bronze coatings. occasionally bronze coatings are used in the jewelry industry as a substitute for expensive silver or allergy-triggering nickel.

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