Method of obtaining a yellow gold alloy deposition by galvanoplasty without using toxic materials

Abstract

The invention concerns the field of galvanic depositions and relates to 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. According to the invention, 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. An electrolytic deposition comprising: a galvanoplastically deposited gold alloy layer, said alloy being a bright 3N colour gold alloy composition of 75% gold, 21% copper, and 4% silver, and being free of cadmium and zinc, said layer being between about 1 m and about 800 m thick, wherein a structure of said alloy composition is formed by dipping an electrode into a bath comprising a proportion of 9.08% gold metal in alkaline aurocyanide form, 90.85% copper metal in alkaline double cyanide form, 0.07% silver metal, organometallic compounds, a wetting agent, a sequestering agent, and free cyanide.

2. The electrolytic deposition, according to claim 1, wherein the structure of said alloy composition is formed when the bath is held at a temperature between about 50 C. and about 80 C., at a pH between about 8 and about 12, and to which a current density of between about 0.05 A/dm.sup.2 and about 1.5 A/dm.sup.2 is applied.

3. A gold alloy layer galvanoplastically deposited on an electrode, the galvanoplastically deposited gold alloy layer comprising: a bright 3N colour gold alloy composition of 75% gold, 21% copper, and 4% silver, and being free of cadmium and zinc, said layer being between about 1 m and about 800 m thick, wherein a structure of said alloy composition is formed from an electrolytic bath comprising a proportion of 9.08% gold metal in alkaline aurocyanide form, 90.85% copper metal in alkaline double cyanide form, and 0.07% silver metal.

4. An electrode, comprising: a galvanoplastically deposited gold alloy layer, said alloy being a bright 3N colour gold alloy composition of 75% gold, 21% copper, and 4% silver, and being free of cadmium and zinc, said layer being between about 1 m and about 800 m thick, wherein a structure of said alloy composition is formed from an electrolytic bath comprising a proportion of 9.08% gold metal in alkaline aurocyanide form, 90.85% copper metal in alkaline double cyanide form, and 0.07% silver metal.

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 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, 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: 55 g.Math..sup.1; Ag: 40 mg.Math.l.sup.1; KCN: 26 g.Math.l.sup.1; pH: 10.5; Temperature: 65 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) 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.

(5) 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.

(6) 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 depositions for this colour, which tend to be depositions of around 75% gold, 12.5% copper and 12.5% silver.

(7) 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.

(8) 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.

(9) 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.

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