US3586611A - Process for the electrolytic deposition of gold-copper-cadmium alloys - Google Patents

Abstract

THE ELECTROLYTIC DEPOSITION OF GOLD-COPPER-CADMIUM ALLOYS ACCORDING TO HEILMANN U.S. PAT. 3,056,733 IS IMPROVED BY INCLUDING SMALL AMOUNTS OF SILVER IN THE AQUEOUS ALKALINE CYANIDE BATH.

Description

United States Patent US. Cl. 204-44 2 Claims ABSTRACT OF THE DISCLOSURE The electrolytic deposition of gold-copper-cadmium alloys according to Heilmann US. Pat. 3,056,733 is improved by including small amounts of silver in the aqueous alkaline cyanide bath.

In Heilmann US. Pat. 3,056,733 (German Pat. 1,141,- 849) there is described a process for the electrolytic deposition of gold-copper-cadmium alloys from an aqueous alkaline cyanide bath by means of a periodically reversed current density using insoluble anodes. This process is characterized by use of a bath containing 1 to 3 grams/ liter of gold as potassium gold cyanide, 5 to 15, preferably 8 to 13 grams/liter of copper as potassium copper cyanide or sodium copper cyanide, 0.1 to 0.8 gram/liter of cadmium as potassium cadmium cyanide or sodium cadmium cyanide and 3 to 8 grams/liter of free cyanide calculated as potassium cyanide. The bath has a pH of 9 to 11 and a current density of 0.5 to 1.5 a./dm. during the cathodic phase of 4 to 20 seconds as well as a current density of 0.75 to 3.75 a./dm. preferably 1.0 to 3.0 a./dm. during the anodic phase of 0.5 to 2 seconds. The ratio of cathodic to anodic current density is preferably less than 1:15.

A disadvantage of the described process consists in that the permanent bright current density range is relatively small so that it can only be used for electroplating small and as much as possible simple formed parts. Besides the deposition of reddish coatings sets tight boundaries for their film thickness and finally the roughness of the coating at greater film thickness are increased.

Unexpectedly it has turned out that these disadvantages can be avoided if one adds a small amount of silver to the bath. This addition can be in the form of potassium silver cyanide or other silver salts compatible with the rest of the bath composition. The concentration of the bath in silver should be between 0.01 and 0.1 gram/liter. This silver content must be maintained over the entire useful life of the bath that the supplemental addition of silver corresponds to an amount of 0.2 to 2% of the content of gold and alloying metals.

Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1 An aqueous bath containing 1.5 grams per liter of gold as potassium gold cyanide, 10.5 grams per liter of copper as potassium copper cyanide, 0.3 gram per liter of cadmium as potassium cadmium cyanide, 0.05 gram per liter of silver as potassium silver cyanide and 5.0 grams per liter of free potassium cyanide was electrolyzed with a cur- Patented June 22, 1971 ice Percent Gold 74 Copper 15 Cadmium 10 Silver 1 A portion of the alloying metals exists in the supplementary additive in the form of a simple, non-cyanide, in aqueous solution acid reacting salt, e.g. salts of sulfuric acid in order to keep the free cyanide content of the bath and the pH value within the necessary limits. The silver content of the bath can be supplemented with the remaining metals or separately.

There are also obtained with film thicknesses of 20 or higher in a relatively wide brilliant current density range, highly lustrous, smooth, yellow to red about 18 carat gold coating of especially high hardness.

The conditions of operation are l to 3 grams per liter of gold as potassium gold cyanide 5 to 15 grams per liter, preferably 8 to 13 grams per liter of copper as potassium copper cyanide or sodium copper cyanide 0.1 to 0.8 gram per liter of cadmium as potassium cadmium cyanide or sodium cadmium cyanide, 0.01 to 0.1 gram per liter of silver as potassium silver cyanide.

3 to 8 grams per liter of free cyanide as potassium cyanide.

Current density of 0.5 to 1.5 a./dm. during the cathodic phase of 4 to 20 seconds.

Current density of 0.75 to 3.75 a./dm. preferably 1.0 to 3.0 a./dm. during the anodic phase of 0.5 to 2 seconds.

The temperature can be between 60 and C.

The supplementary additive can for instance consist in two solutions. The first of these solutions contains 40 grams per liter of gold as potassium gold cyanide, 0.5 gram per liter of silver as potassium silver cyanide and 10 grams per liter of copper as potassium copper cyanide or sodium copper cyanide. The second solution contains 3 grams per liter of cadmium as cadmium sulfate or cadmium nitrate or cadmium acetate. For supplementation equal amounts of the two solutions are added to the bath.

What is claimed is:

1. In a process for the electrolytic deposition of goldcopper-cadmium alloys from aqueous alkaline cyanide baths using periodically reversed direct current, the steps which comprise electrolytically depositing a gold-coppercadmium alloy from an aqueous cyanide bath maintained at a pH of 9-11 and containing 1 to 3 grams per liter of gold as potassium gold cyanide, 5 to 15 grams per liter of copper as potassium or sodium copper cyanide. 0.1 to 0.8 gram per liter of cadmium as potassium or sodium cadmium cyanide, 0.01 to 0.1 gram per liter of silver as potassium silver cyanide and 3 to 8 grams per liter of free cyanide as potassium cyanide, the duration of each cathodic phase being 4 to 20 seconds and the duration of each anodic phase being 0.5 to 2 seconds and maintaining References Cited a current density of 0.5 to 1.5 a./dm. during the cathodic phase and a current density of 0.75 to 3.75 a./dm. during UNITED f PATENTS the anodic phase 3,056,733 10/1962 Hellmann 20444 2. A process according to claim 1 wherein the bath 5 concentration is maintained by adding supplementary ad- GERALD KAPLAN Primary Exammer ditives containing salts of gold, silver, cadmium and copper U S Cl X R and wherein the silver is 0.2 to 2% based on the total of 75 165 t the gold and alloying metals.