METHOD OF OBTAINING A YELLOW GOLD ALLOY DEPOSITION BY GALVANOPLASTY WITHOUT USING TOXIC MATERIALS

Abstract

A method of galvanoplastic deposition of a gold alloy on an electrode dipped into a bath including metal gold in alkaline aurocyanide form, organometallic compounds, a wetting agent, a sequestering agent and free cyanide, where the alloy metals are copper, in double copper and potassium cyanide form, and silver in cyanide form, allowing a mirror bright yellow gold alloy to be deposited on the electrode.

Claims

1: A method for the galvanoplastic deposition of a gold alloy on an electrode, the method comprising: (a) dipping an electrode into a bath, wherein the bath comprises: gold metal in alkaline aurocyanide form, copper metal in copper and double potassium cyanide form, silver metal in cyanide form, organometallic compounds, a wetting agent, a sequestering agent, and free cyanide, wherein the bath has a proportion of 9.08% gold, 90.85% copper, and 0.07% silver, and the bath does not comprise cadmium or zinc; and then, (b) galvanoplastically depositing a bright 3N colour gold alloy made of 75% gold, 21% copper, and 4% silver on the electrode, wherein the gold alloy has a thickness of 200 to 800 m.

2: The method according to claim 1, wherein the bath comprises 5.5 g.Math.l.sup.1 of gold metal in alkaline aurocyanide form, 55 g.Math.l.sup.1 of copper metal in copper and double alkaline cyanide form, and 40 mg.Math.l.sup.1 of silver metal in cyanide form.

3: The method according to claim 2, wherein the bath comprises from 15 to 35 g.Math.l.sup.1 of cyanide.

4: The method according to claim 1, wherein a concentration of the wetting agent is between 0.05 and 10 ml.Math.l.sup.1.

5: The method according to claim 1, wherein the wetting agent is selected from the group consisting of poly-oxy-alkenic, ether phosphate, lauryl sulphate, dimethyldodecylamine-N-oxide, and a dimethyl(dodecyl) ammonium propane sulfonate.

6: The method according to claim 1, wherein the bath further comprises an amine, and wherein a concentration of the amine is between 0.01 and 5 ml.Math.l.sup.1.

7: The method according to claim 1, wherein the bath further comprises a depolariser, and wherein a concentration of the depolariser is between 0.1 mg.Math.l.sup.1 to 20 mg.Math.l.sup.1.

8: The method according to claim 1, wherein the bath further comprises at least one conductive salt selected from the group consisting of a phosphate, a carbonate, a citrate, a sulphate, a tartrate, a gluconate, and a phosphonate conductive salt.

9: The method according to claim 1, wherein the temperature of the bath is kept between 50 and 80 C.

10: The method according to claim 1, wherein the pH of the bath is kept between 8 and 12.

11: The method according to claim 1, wherein the galvanoplastically depositing (b) is performed at a current density of between 0.3 A.Math.dm.sup.2.

12-13. (canceled)

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The invention concerns an electrolytic deposition of a gold alloy with a 3N colour which, surprisingly, includes AuCuAg as its main compounds in proportions that are not known, to obtain the 3N colour, i.e. bright yellow.

[0023] In the example deposition above, there is a gold alloy, free of toxic metals or metalloids, and in particular free of cadmium, with a 3N yellow colour, a thickness of 200 microns, excellent brightness and with a very high level of resistance to wear and tarnishing.

[0024] This deposition is obtained by electrolysis in an electrolytic bath of the type; [0025] Au; 5.5 g.Math.l.sup.1; [0026] Cu: 55 g.Math.l.sup.1; [0027] Ag-40 mg.Math.l.sup.1; [0028] KCN: 26 g.Math.l.sup.1; [0029] pH: 10.5; [0030] Temperature: 65 C.; [0031] Current density: 0.3 A.Math.dm.sup.2; [0032] Wetting agent: 0.05 ml.Math.l.sup.1 NN_Dimethyldodecyl N-oxide; [0033] Iminodiacetic: 20 g.Math.l.sup.1; [0034] Ethylenediamene: 0.5 ml.Math.l.sup.1; [0035] Gallium, selenium or tellurium: 10 mg.Math.l.sup.1.

[0036] The electrolysis is preferably followed by a heat treatment at a temperature of between 200 and 453 degrees Celsius for 1 to 30 minutes in order to obtain a deposition of optimum quality.

[0037] These conditions provide a cathodic yield of 98 mg.Math.A.Math.min.sup.1 with a deposition speed of around 10 m per hour in the case of the example.

[0038] Thus, surprisingly, the bath according to the invention provides a deposition in proportions of around 75% gold, 21% copper and 4% silver, corresponding to a 3N colour, 18 carat deposition, very different proportions from the usual electrolytic depositons for this colour, which tend to be depositions of around 75% gold, 12.5% copper and 12.5% silver.

[0039] The bath may also contain a brightener. This is preferably a butynediol derivative, a pyridinio-propanesulfonate or a mixture of the two, a tin salt, sulfonated castor oil, methylimidozole, dithiocarboxylic acid such as thiocarbamide, thiobarbituric acid, imidazolidinthion or thiomalic acid.

[0040] In these examples, the electrolytic bath is contained in a polypropylene or PVC bath holder with a heat insulating coating. The bath is heated using quartz, PTFE, porcelain or stabilised stainless steel thermo-plungers. Good cathodic rod movement and electrolyte flow must be maintained. The anodes are made of platinum plated titanium, stainless steel, ruthenium, iridium or alloys of the latter two.

[0041] Of course, the present invention is not limited to the illustrated example but is capable of various variants and alterations which will be clear to those skilled in the art. In particular, the bath may contain the following metals: Zr, Se, Te, Sb, Sn, Ga, As, Sr, Be, Bi in negligible quantities.

[0042] Moreover, the wetting agent may be of any type that can wet in an alkaline cyanide medium.