Method of obtaining a 18 caracts 3N gold alloy

Abstract

A method for the galvanoplastic deposition of a gold alloy on an electrode dipped into a bath including gold metal, organometallic compounds, a wetting agent, a sequestering agent and free cyanide, the alloy metals being copper metal and silver metal allowing a mirror-bright yellow gold alloy to be deposited on the electrode characterized in that the bath respects a proportion of 21.53% gold, 78.31% copper and 0.16% silver.

Claims

1. A method for the galvanoplastic deposition of a 3N yellow gold alloy on an electrode, the method comprising: (a) providing an electrode; (b) dipping the electrode into a bath, wherein the bath includes gold metal, copper metal, silver metal, organometallic compounds, a wetting agent, a sequestering agent and free cyanide; and (c) galvanoplastically depositing a 3N yellow gold alloy on the electrode, wherein the bath has a proportion of 21.53% gold, 78.31% copper and 0.16% silver, wherein the deposited 3N yellow gold alloy is made of 75% gold, 19% copper and 6% silver.

2. The method according to claim 1, wherein the bath includes from 1 to 10 g.Math.l.sup.1 of gold metal in double gold and potassium cyanide form.

3. The method according to claim 1, wherein the bath includes from 10 to 60 g.Math.l.sup.1 of copper metal in copper iodide form.

4. The method according to claim 1, wherein the bath includes from 10 mg.Math.l.sup.1 to 1 g.Math.l.sup.1 of silver metal in double silver and potassium cyanide form.

5. The method according to claim 1, wherein the bath includes from 3 to 35 g.Math.l.sup.1 of free cyanide.

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

7. 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 dimethyl(dodecyl) ammonium propane sulfonate.

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

9. The method according to claim 1, wherein the bath further includes a concentration of a depolariser of between 0.1 to 20 mg.Math.l.sup.1.

10. The method according to claim 1, wherein the bath further includes phosphate, carbonate, citrate, sulphate, tartrate, gluconate and/or phosphonate conductive salts.

11. The method according to claim 1, wherein the temperature of the bath is kept between 50 and 90 C.

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

13. The method according to claim 1, wherein the method is performed at a current density of between 0.05 to 1.5 A.Math.dm.sup.2.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

(3) This deposition is obtained by electrolysis in an electrolytic bath of the type: Au: 5.5 g.Math.l.sup.1; Cu: 20 g.Math.l.sup.1; Ag: 40 mg.Math.l.sup.1; CN: 5 g.Math.l.sup.1; pH: 10.5; Temperature: 80 C.; Current density: 0.3 A.Math.dm.sup.2; Wetting agent: 0.05 ml.Math.l.sup.1 NN-Dimethyldodecyl N-oxide; Iminodiacetic: 20 g.Math.l.sup.1; Ethylenediamene: 0.5 ml.Math.l.sup.1; Gallium, selenium or tellurium: 10 mg.Math.l.sup.1.

(4) Consequently, the bath respects a proportion of 21.53% gold, 78.31% copper and 0.16% silver between its main compounds.

(5) The electrolysis is preferably followed by a heat treatment at a temperature of between 200 and 450 degrees Celsius for 1 to 30 minutes in order to obtain a deposition of optimum quality.

(6) These conditions provide a cathodic yield of 95 mg.Math.A.Math.min.sup.1 with a deposition speed of around 10 m per hour in the case of the example.

(7) Thus, surprisingly, the bath according to the invention provides a deposition in proportions of around 75% gold, 19% copper and 6% silver, corresponding to a 3N colour, 18 carat deposition, very different proportions from the usual electrolytic depositions for this colour, which tend to be depositions of around 75% gold, 12.5% copper and 12.5% silver.

(8) 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.

(9) 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.

(10) 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.

(11) Moreover, the wetting agent may be of any type that can wet in an alkaline cyanide medium.