Method of obtaining a yellow gold alloy deposition by galvanoplasty without using toxic metals or metalloids

Abstract

A galvanic bath, containing: gold metal in the form of alkaline aurocyanide; organometallic components; a wetting agent; a complexing agent; free cyanide; copper metal in the form of copper II cyanide and potassium; and indium metal in the form of a complex indium metal, where the galvanic bath does not contain cadmium and zinc, and where the galvanic bath deposits a yellow gold alloy comprising gold, copper, and indium as main components.

Description

FIELD OF THE INVENTION

The invention relates to an electrolytic deposition in the form of a thick gold alloy layer and the manufacturing method thereof.

BACKGROUND OF THE INVENTION

In the field of decorative plating, methods are known for producing gold electrolytic depositions that are yellow with a fineness greater than or equal to 9 carats, ductile with a thickness of 10 microns, and with a high level of tarnish resistance. These depositions are obtained by electrolysis in an alkaline galvanic bath containing 0.1 to 3 g/l of cadmium, in addition to gold and copper. The depositions obtained via these known methods have however cadmium levels of between 1 and 10%. Cadmium facilitates the deposition of thick layers, i.e. between 1 and 800 microns and provides a yellow alloy by reducing the quantity of copper contained in the alloy, however, cadmium is extremely toxic and prohibited in some countries.

Other known yellow depositions are alloys comprising gold and silver.

18 carat gold alloys containing copper and zinc and no cadmium are also known. However, these depositions are too pink (fineness too copper rich). Finally, these depositions have poor resistance to corrosion which means that they tarnish quickly.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome all or part of the aforementioned drawbacks by proposing a method for depositing a thick gold alloy layer that is yellow and has neither zinc nor cadmium as main components.

The invention thus relates to an electrolytic deposition in the form of a gold alloy, whose thickness is comprised between 1 and 800 microns and includes copper, characterized in that it includes indium as the third main component.

According to other advantageous features of the invention:

• • the deposition is substantially free of toxic metals or metalloids;
  • the deposition includes a colour comprised within the fields of 1N and 3N (in accordance with ISO standard 8654);
  • the deposition is shiny and is highly resistant to corrosion.

The invention also relates to a method for the galvanoplasty deposition of a gold alloy on an electrode dipped in a bath including gold metal in the form of aurocyanide alkaline, organometallic components, a wetting agent, a complexing agent and free cyanide, characterized in that the alloy metals are copper in the form of the copper II cyanide and potassium, and indium in complex aminocarboxylic or aminophosphoric form for depositing a shiny reflective yellow type gold alloy.

According to other advantageous features of the invention:

the bath includes from 1 to 10 g·l⁻¹ of gold metal in the form of alkaline aurocyanide and preferably 5 g·l⁻¹;

the bath includes from 30 to 80 g·l⁻¹ of alkaline copper II cyanide and preferably 50 g·l⁻¹;

the bath includes from 10 mg·l⁻¹ to 5 g·l⁻¹ of indium metal in complex form and preferably includes 1 g·l⁻¹;

the bath includes 15 to 35 g·l⁻¹ of free cyanide;

the wetting agent includes a concentration of between 0.05 to 10 ml·l⁻¹ and preferably 3 ml·l⁻¹;

the wetting agent is selected from among polyoxyalkylenic, ether phosphate, lauryl sulphate, dimethyldodecylamine-N-oxide, dimethyl-dodecyl ammonium propane sulfonate types or any other type able to wet in an alkaline cyanide medium;

the aminocarboxylic complexing agent includes a concentration of between 0.1 and 20 g·l⁻¹;

the bath includes an amine in a concentration of between 0.01 and 5 ml·l⁻¹

the bath includes a depolariser in a concentration of between 0.1 mg·l⁻¹ and 20 mg·l⁻¹;

the bath includes conductive salts of the following types: phosphates, carbonates, citrates, sulphates, tartrates, gluconates and/or phosphonates;

the temperature of the bath is maintained between 50 and 80° C.;

the pH of the bath is maintained between 8 and 12;

the method is carried out at current densities of between 0.2 and 1.5 A·dm⁻².

The electrolysis is preferably followed by a thermal treatment at least 450 degrees Celsius for at least 30 minutes in order to obtain optimum deposition quality.

The bath may also contain a brightener. The brightener is preferably a butynediol derivative, a pyridinio-propane sulfonate or a mixture of the two, a tin salt, sulfonated castor oil, methylimidazole, dithiocarboxylic acid, such as thiourea, thiobarbituric acid, imidazolidinethione or thiomalic acid.

In particular, in accordance with a non-limiting illustrative embodiment of the present invention, a method for galvanoplasty deposition of a gold alloy on an electrode dipped in a bath including gold metal in the form of alkaline aurocyanide, organometallic components, a wetting agent, a complexing agent and free cyanide is provided, wherein the method is characterized in that the alloy metals are copper in the form of copper II cyanide and potassium, and complex indium for depositing a shiny reflective yellow type gold alloy on the electrode. In accordance with a second non-limiting illustrative embodiment of the present invention, the first non-limiting embodiment is modified so that the complex indium is of the aminocarboxylic or aminophosphonic type. In accordance with a third non-limiting illustrative embodiment of the present invention, the first and second non-limiting embodiments are further modified so that the bath includes from 1 to 10 g·l⁻¹ of gold metal in the form of alkaline aurocyanide.

In accordance with a fourth non-limiting illustrative embodiment of the present invention, the first, second, and third non-limiting embodiments are further modified so that the bath includes from 30 to 80 g·l⁻¹ of copper II metal in the form of alkaline cyanide. In accordance with a fifth non-limiting illustrative embodiment of the present invention, the first, second, third, and fourth non-limiting embodiments are further modified so that the bath includes from 10 mg·l⁻¹ to 5 g·l⁻¹ of complex indium metal. In accordance with a sixth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth and fifth non-limiting embodiments are modified so that the bath includes from 15 to 35 g·l⁻¹ of free cyanide. In accordance with a seventh non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth and sixth non-limiting embodiments are further modified so that the wetting agent includes a concentration of between 0.05 and 10 ml·l⁻¹.

In accordance with an eighth non-limiting illustrative embodiment of the present invention, the first or seventh non-limiting embodiments are further modified so that the wetting agent is chosen from among the following types: polyoxyalcoylenic, ether phosphate, lauryl sulphate, dimethyledodecylamine N oxide, and dimethyldodecyl ammonium propane sulfonate. In accordance with a ninth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh and eighth non-limiting embodiments are further modified so that the bath includes an amine concentration of between 0.01 to 5 ml·l⁻¹. In accordance with a tenth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth and ninth non-limiting embodiments are further modified so that the bath includes an amine concentration of between 0.01 mg·l⁻¹ to 20 mg·l⁻¹. In accordance with an eleventh non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth non-limiting embodiments are further modified so that the bath includes a depolarising concentration of between 0.1 mg·l⁻¹ to 20 mg·l⁻¹. In accordance with a twelfth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth and eleventh non-limiting embodiments are further modified so that the bath includes conductive salts of the following types: phosphates, carbonates, citrates, sulphates, tartrates, gluconates and/or phosphonates.

In accordance with a thirteenth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh and twelfth non-limiting embodiments are further modified so that the temperature of the bath is maintained between 50° C. and 80° C. In accordance with a fourteenth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth and thirteenth non-limiting embodiments are further modified so that the pH of the bath is maintained between 8 and 12. In accordance with a fifteenth non-limiting illustrative embodiment of the present invention, the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth, thirteenth and fourteenth non-limiting embodiments are further modified so that the method is performed with a current density of between 0.2 and 1.5 A·dm⁻². In accordance with a sixteenth non-limiting illustrative embodiment of the present invention, an electrolytic deposition in the form of a gold alloy is provided, wherein the electrolytic deposition is obtained from a method according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth, thirteenth, fourteenth and fifteenth non-limiting embodiments of the present invention, wherein the electrolytic deposition has a thickness of between 1 and 800 microns and the electrolytic deposition includes copper, wherein the electrolytic deposition is characterized by including indium as a third main compound for obtaining a shiny colour that is between the fields 1N and 3N.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an example deposition, there is a gold alloy, free of toxic metals or metalloids, in particular free of cadmium, with a 2N yellow colour, a thickness of 200 microns, excellent brilliance and highly wear and tarnish resistant.

This deposition is obtained by electrolysis in an electrolytic bath of the following type:

Example 1

Au: 3 g·l⁻¹

Cu: 45 g·l⁻¹

In: 0.1 g·l⁻¹

KCN: 22 g·l⁻¹

pH: 10.5

Temperature: 65° C.

Current density: 0.5 A·dm⁻²

Wetting agent: 0.05 ml·l⁻¹ NN-Dimethyldodecyl N Oxide

Iminodiacetic: 20 g·l⁻¹

Ethylenediamine: 0.5 ml·l¹

Potassium selenocyanate: 1 mg·l⁻¹

Example 2

Au: 6 g·l⁻¹

Cu: 60 g·l⁻¹

In: 2 g·l⁻¹

KCN: 30 g·l⁻¹

NTA: 4 g·l⁻¹

Ag: 10 mg·l⁻¹

Diethylentriamine: 0.2 ml·l⁻¹

Gallium, selenium or tellurium: 5 mg·l⁻¹

Sodium hypophosphite: 0.1 g·l⁻¹

Thiomalic acid: 50 mg·l⁻¹

Current density: 0.5 A·dm⁻²

Temperature: 70° C.

pH: 10.5

Wetting agent: 2 ml·l⁻¹ ether phosphate

In these examples, the electrolytic bath is contained in a polypropylene or PVC bath holder with heat insulation. The bath is heated using quartz, PTFE, porcelain or stabilised stainless steel thermo-plungers. Proper cathodic agitation and electrolyte flow must be maintained. The anodes are made of platinum plated titanium, stainless steel, ruthenium, iridium or alloys thereof.

Under such conditions, cathodic efficiency of 62 mg·A·min⁻¹ can be obtained, with a deposition speed of 1 μm in 30 minutes in example 1 and, in example 2, a shiny deposition of 10 μm in 30 minutes.

Of course, this 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 negligible quantities of the following metals: Ag, Cd, Zr, Se, Te, Sb, Sn, Ga, As, Sr, Be, Bi. Moreover, the wetting agent may be of any type able to wet in an alkaline cyanide medium.

Most generally, the invention concerns the field of electroplating methods, and relates to an electrolytic deposition in the form of a gold alloy with a thickness of between 1 and 800 microns and that includes copper. According to the invention, the deposition includes indium as a third main compound.

Claims

1. A galvanic bath, comprising: gold metal in the form of alkaline aurocyanide;organometallic components;a wetting agent;a complexing agent;free cyanide;copper metal in the form of copper II cyanide and potassium; andindium metal in the form of a complex indium metal,wherein the galvanic bath does not comprise cadmium and zinc,wherein the galvanic bath may optionally comprise silver only in negligible quantity,and wherein the galvanic bath deposits a yellow gold alloy comprising gold, copper, and indium as main components.

2. The galvanic bath according to claim 1, wherein the complex indium metal comprises an aminocarboxylic group or an aminophosphonic group.

3. The galvanic bath according to claim 2, wherein the aminocarboxylic group, in complex form, is present in the galvanic bath at a concentration of between 0.1 g·l−1 to 20 g·l−1.

4. The galvanic bath according to claim 1, wherein the galvanic bath comprises from 30 to 80 g·l−1 of copper metal in the form of the copper II cyanide and potassium.

5. The galvanic bath according to claim 1, wherein the galvanic bath comprises from 10 mg·l−1 to 5 g·l−1 of the complex indium metal.

6. The galvanic bath according to claim 1, wherein the galvanic bath comprises from 15 to 35 g·l−1 of the free cyanide.

7. The galvanic bath according to claim 1, wherein the wetting agent is present in the galvanic bath at a concentration of between 0.05 to 10 ml·l−1.

8. The galvanic bath according to claim 7, wherein the wetting agent is selected from the group consisting of: polyoxyalkylenic, ether phosphate, lauryl sulphate, dimethyldodecylamine N oxide and dimethyldodecyl ammonium propane sulfonate.

9. The galvanic bath according to claim 1, wherein the galvanic bath further comprises an amine concentration of between 0.01 and 5 ml·l−1.

10. The galvanic bath according to claim 1, wherein the galvanic bath further comprises a depolarising agent in a concentration of between 0.1 mg·l−1 to 20 mg·l−1.

11. The galvanic bath according to claim 1, wherein the galvanic bath further comprises conductive salts selected from the group consisting of: phosphates, carbonates, citrates, sulphates, tartrates, gluconates and phosphonates.

12. The galvanic bath according to claim 1, wherein the galvanic bath comprises from 1 to 10 g·l−1 of the gold metal in the form of alkaline aurocyanide.

13. The galvanic bath according to claim 1, wherein the galvanic bath further comprises an additional metal selected from the group consisting of: Zr, Se, Te, Sb, Sn, Ga, As, Sr, Be and Bi, wherein the individual weight concentrations of gold, copper and indium in the galvanic bath are each greater than the weight concentration of the additional metal.

14. The galvanic bath according to claim 1, wherein the galvanic bath does not comprise silver.