Rhodium sulfate compounds and rhodium plating

Details Rhodium sulfate compounds and rhodium plating Rhodium sulfate compounds and rhodium plating

1999-05-06

2001-06-05

Gorgos, Kathryn (Department: 1741)

Electrolysis: processes, compositions used therein, and methods

Electrolytic coating

Depositing predominantly single metal coating

Reexamination Certificate

active

06241870

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to methods for electroplating rhodium, and to new rhodium compounds and electrolytes for use in electroplating rhodium.
BACKGROUND OF THE INVENTION
Rhodium plated electrodes are used in the soda industry for electrolysis of salt water, and for electrodes for domestic water treatment. Rhodium plating is used widely in the jewelry industry. In the electronics industry, rhodium plating is used for electrical contacts in, e.g., ferreed switches.
It is known that rhodium metal tends to electroplate with high stress. This limits the thickness range over which electroplated layers can be produced without cracking. Moreover, the brightness of conventionally plated rhodium layers declines as the plating thickness increases. Accordingly the thickness of bright rhodium electroplated layers is typically limited to approximately 20 microinches or less. While this thickness may be suitable for some applications, thicker plated layers which retain the brightness of thin layers and are crack free would be desirable for nearly all applications.
STATEMENT OF THE INVENTION
We have developed an electroplating process for rhodium metal which produces relatively low stress electroplated layers that are full bright over a thickness range of 0.1-60 microinches. A feature of the process is the use of a novel rhodium sulfate compound in the electrolyte and the technique for preparing the novel rhodium sulfate compound. In the new rhodium sulfate compound the rhodium sulfate molecules complex with a minimum of metal to metal bonding, with the complex forming predominantly via bridged bidentate sulphato groups. This result is achieved by carefully controlling the hydrolysis of the rhodium sulfate in preparing the electrolyte.


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P. J. Durrant, B. Durrant. Introduction to Advanced Inorganic Chemistry. 2nd edition. 1970, pp. 709 —Month not available—.

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