# US 4,391,679 A · Electrolytic bath and process for the deposition of gold alloy coatings

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- Number: US 4,391,679 A
- Document ID: US4391679A
- Status: Granted
- Kind: A
- Application number: 06/250,142
- Filed: 1981-04-02
- Granted: 1983-07-05
- Earliest claimed: 1980-04-03
- Assignees: Degussa AG
- Inventors: Wolfgang Zilske; Werner Kuhn
- Web page: https://patentgrep.com/patent/US4391679A

## CPC

- C25D 3/62: containing more than 50% by weight of gold
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR

## Abstract

In the electro industry, there are needed acid gold alloy baths which give glossy, ductile coatings, operate at high current densities, and contain little non-metallic impurities. This is attained by a bath based on potassium cyanoaurate (III) and an acid whereby the bath contains at least one of the alloying metals cobalt, nickel, indium, tin, zinc, or cadmium in the form of a water soluble salt, together with an amine, an aminocarboxylic acid, or a phosphonic acid and has a pH of below 3.

## Claims

### Claim 1

A gold bath suitable for the deposition of high gloss and ductile gold alloy coatings consisting of either (1) water, potassium cyanoaurate (III), at least one alloying element selected from the group consisting of cobalt, nickel, indium, zinc, and cadmium in the form of a water soluble salt together with a hydrocarbyl amine, an aminocarboxylic acid, or a phosphonic acid which forms a complex with the alloying element and 20-200 g/l of sulfuric acid, phosphoric acid, citric acid or a mixture thereof, or (2) the gold bath (1) together with potassium dihydrogen phosphate, potassium hydrogen sulfate or potassium citrate, said bath having a pH of less than 3.

### Claim 2 (depends on 1)

A gold bath according to claim 1 wherein the bath has a pH between 0.4 and 2.5.

### Claim 3 (depends on 2)

A gold bath according to claim 2 wherein the pH is between 0.6 and 2.0.

### Claim 4 (depends on 2)

A gold bath according to claim 2 wherein the bath contains 1-20 g/l of gold in the form of potassium cyanoaurate (III).

### Claim 5 (depends on 4)

A gold bath according to claim 4 which contains potassium dihydrogen phosphate, potassium hydrogen sulfate, or potassium citrate.

### Claim 6 (depends on 5)

A gold bath according to claim 5, including 0.1-20 g/l of the alloying element in the form of a water soluble salt.

### Claim 7 (depends on 6)

A gold bath according to claim 6, including 1-100 g/l of the amine, aminocarboxylic acid, or phosphonic acid.

### Claim 8 (depends on 4)

A gold bath according to claim 4, including 0.1-20 g/l of the alloying element in the form of a water soluble salt.

### Claim 9 (depends on 8)

A gold bath according to claim 8, including 1-100 g/l of the amine, aminocarboxylic acid, or phosphonic acid.

### Claim 10 (depends on 1)

A gold bath according to claim 1 which is gold bath (1).

### Claim 11 (depends on 1)

A gold bath according to claim 1 wherein the alloying element is cobalt.

### Claim 12 (depends on 1)

A gold bath according to claim 1 wherein the alloying element is nickel.

### Claim 13 (depends on 1)

A gold bath according to claim 1 wherein the alloying element is indium.

### Claim 14 (depends on 7)

A process of depositing a high gloss and ductile gold alloy coating on a base metal comprising employing the gold bath of claim 7 with an electric current at a temperature of 40.degree.-60.degree. C.

### Claim 15 (depends on 14)

A process according to claim 14 wherein the current density is 0.1-20 A/dm.sup.2.

### Claim 16 (depends on 9)

A process of depositing a high gloss and ductile gold alloy coating on a base metal comprising employing the gold bath of claim 9 with an electric current at a temperature of 40.degree.-60.degree. C.

### Claim 17 (depends on 16)

A process according to claim 16 wherein the current density is 0.1-20 A/dm.sup.2.

### Claim 18 (depends on 9)

A process of depositing a high gloss and ductile coating on a base metal comprising employing the gold bath of claim 9 with an electric current at a current density of 0.1-20 A/dm.sup.2.

### Claim 19 (depends on 1)

A process of depositing a high gloss and ductile gold alloy coating on a base metal comprising employing the gold bath of claim 1 with an electric current at a temperature of 40.degree.-60.degree. C.

### Claim 20 (depends on 19)

A process according to claim 19 wherein the current density is 0.1-20 A/dm.sup.2.