NOBLE METAL SALT PREPARATION, A METHOD FOR PRODUCTION THEREOF AND USE FOR ELECTROPLATING

Abstract

The present invention relates to a method for production of a noble metal salt preparation, the noble metal salt preparation comprising at least one noble metal sulfonate and thiourea and the use for surface coating by electroplating or electroless plating of a noble metal or metal alloy.

Claims

1. A method for production of a noble metal salt preparation by membrane electrolysis comprising the steps: a) providing an electrolytic cell comprising an anode comprising a noble metal and a cathode, wherein an anodic region and cathodic region are separated by a membrane; b) providing of at least one sulfonate solution in the anodic region; and c) anodic oxidation of the noble metal and formation of a noble metal salt preparation comprising a noble metal sulfonate by passing a current through the electrolytic cell, wherein thiourea is added in the anodic region after step b) or after step c), and wherein the concentration of thiourea is 0.005 g/l to 200 g/l.

2. The method for production of a noble metal salt preparation of claim 1, wherein the noble metal is selected from gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and indium (In).

3. The method for production of a noble metal salt preparation of claim 1, wherein the membrane is a cation-exchange membrane or an anion-exchange membrane.

4. The method for production of a noble metal salt preparation of claim 1, wherein the sulfonate is an alkyl sulfonate.

5. The method for production of a noble metal salt preparation of claim 1, wherein the concentration of the at least one sulfonate solution is 0.1% (w/w) to 20% (w/w).

6. The method for production of a noble metal salt preparation of claim 1, wherein the method comprises at least one further step selected from precipitation, flocculation, complexation, oxidation and/or reduction.

7. A noble metal salt preparation comprising at least one noble metal sulfonate and thiourea, wherein the molar ratio of noble metal to thiourea is 10.000:1 to 1:10.

8. The noble metal salt preparation of claim 7, wherein the noble metal salt preparation is an aqueous, organic or ionic solution with a concentration of the noble metal of 0.001 mol/l to 5 mol/l.

9. The noble metal salt preparation of claim 7, wherein the noble metal sulfonate is selected from gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and indium (In) sulfonates.

10. The noble metal salt preparation of claim 7, wherein the pH value is pH 1 to pH 8.

11. The noble metal salt preparation of claim 7, comprising at least one further complexing agent.

12. The noble metal salt preparation of claim 7, wherein the stability of an aqueous solution of the noble metal salt preparation is at least one or more months.

13. The noble metal salt preparation according to claim 12 wherein the stability of an aqueous solution of the noble metal salt preparation is at least one year.

14. A method for electroplating of a noble metal or metal alloy comprising the steps: a) providing an electroplating bath comprising an anode, a cathode and a solution of at least one noble metal salt preparation according to claim 7; b) applying a current to the electroplating bath, whereby the at least one noble metal forms on the cathode; and c) removing the cathode from the electroplating bath.

15. A method for electroless plating of a noble metal comprising the steps: a) providing a plating bath comprising a solution of a noble metal salt preparation according to claim 7; b) contacting a solid substrate with the plating bath, whereby the noble metal forms on the solid substrate; and c) removing the solid substrate from the plating bath.

16. The method for production of a noble metal salt preparation of claim 4, wherein the sulfonate is a C1- to C10-alkyl sulfonate.

17. The noble metal salt preparation of claim 8, wherein the noble metal salt preparation has a concentration of the noble metal of 0.01 mol/l to 0.5 mol/l.

18. The noble metal salt preparation of claim 11, wherein the at least one further complexing agent is selected from chelating agents and organosulfur compounds.

19. The noble metal salt preparation of claim 11, wherein the at least one further complexing agent is selected from methylglycinediacetic acid or ethylenediamine-N,N-disuccinic acid (EDDS) or an alkali or alkaline earth salt of these acids, methionine or cysteine.

20. The method for production of a noble metal salt preparation of claim 1, wherein: the noble metal is selected from gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and indium (In); the membrane is a cation-exchange membrane or an anion-exchange membrane; the sulfonate is an alkyl sulfonate; and the concentration of the at least one sulfonate solution is 0.1% (w/w) to 20% (w/w).

Description

[0078] The present invention will now be further explained by the following non-limiting figures and examples.

[0079] FIG. 1 shows a schema of the electrolytic cell comprising an anode comprising a noble metal and a cathode, wherein the anodic region and the cathodic region are separated by a membrane.

PRODUCTION OF AN Au (I) SALT SOLUTION

[0080] For the production of Au (I) salt solutions the electrolytic cell of FIG. 1 was used. The electrolytic cell comprises an anode comprising gold with a high surface, which is produced according to known procedures, in particular by the Wohlwill process (Gmelin 1974), and a cathode, wherein the anodic region and the cathodic region are separated by a membrane. In the anodic region, the electrolyte is an alkyl sulfonic acid and thiourea. In the cathodic region, the electrolyte is an alkyl sulfonic acid.

[0081] The anodic oxidation is carried out with direct current of 0.5 A, 1 A or 10 A. The membrane electrolysis is carried out at 25 C. Alternatively, the membrane electrolysis can be carried out at temperatures between 20 C. and 80 C.

[0082] In the anodic region, the Au (I) salt solution is received and filtrated.

EXAMPLE 1: PREPARATION OF Au(I) METHANESULFONATE

[0083] The catholyte is mixed of 70% methane sulfonic acid and distilled water to a solution of 5% methane sulfonic acid. The anolyte comprises an aqueous solution of methane sulfonic acid (5%) with 20 g/l thiourea. Platinated titanium was used as cathode and the anode was pure gold from the Wohlwill process. The membrane between cathode and anode was a cation selective membrane from DuPont (Nafion).

[0084] The anodic oxidation is carried out with direct current of 1.0 A for two hours. Afterwards the anolyte contained 13.9 g gold as gold (I).

EXAMPLE 2 PREPARATION Au(I) METHANESULFONATE

[0085] The catholyte is mixed of 70% methane sulfonic acid and distilled water to a solution of 20% methane sulfonic acid. The anolyte comprises an aqueous solution of methane sulfonic acid (20%) with 40 g/l thiourea. Platinated titanium was used as cathode and the anode was pure gold from the Wohlwill process. The membrane between cathode and anode was a cation selective membrane from DuPont (Nafion).

[0086] The anodic oxidation is carried out with direct current of 1.0 A for five hours. Afterwards the anolyte contained 33.1 g gold as gold (I).

EXAMPLE 3 PREPARATION Au(I) METHANESULFONATE

[0087] The catholyte and anolyte are 100% methane sulfonic acid. Platinated titanium was used as cathode and the anode was pure gold from the Wohlwill process. The membrane between cathode and anode was a cation selective membrane from DuPont (Nafion).

[0088] The anodic oxidation is carried out with direct current of 0.5 A for four hours. Afterwards the anolyte contained 13.4 g gold as gold (I) and was diluted with distilled water with solved thiourea in a concentration of 20 g/l.

EXAMPLE 4 ELECTROPLATING

[0089] The Au(I) methanesulfonate solution of example 1 was used for electroplating a nickel plated messing plate in a regular Hull Cell. The Au (I) plating solution comprised 2 g/l Au (I), 5 g/l thiourea, 5 g/l sodium methanesulfonate and 5 ml of a 0.005% solution of sodium dodecyl sulfate. After plating with 0.5 A/dm.sup.2 for 5 min the cathodic nickel/messing plate was yellow by the gold plating.

EXAMPLE 5 ELECTROLESS PLATING

[0090] The Au(I) methanesulfonate solution of example 2 was used for electroless plating a nickel plated printed circuit board in a regular beaker. The Au (I) plating solution comprised 2 g/l Au (I), 5 g/l thiourea, 2 g/l Trilon M and 5 ml 0.005% solution of sodium dodecyl sulfate. After heating to 62 C. and plating for 5 min the printed circuit board was yellow by the gold plating.

[0091] Cited Non-Patent Literature

[0092] OECD (1992) OECD Guideline for testing of chemicals, Section 3-Degradation and Accumulation, Test No. 301: Ready Biodegradability, DOI: 10.1787/9789264070349-en.

[0093] Gmelin L (1974) Gmelin Handbuch der anorganischen Chemie: Gold. Lieferung 2, Springer-Verlag Berlin Heidelberg GmbH, 8th Edition, ISBN 3-540-93265-8.

REFERENCE SIGNS

[0094] 1 Cathode [0095] 2 Anode [0096] 3 Membrane [0097] 4 Catholyte [0098] 5 Anolyte