Process of electroplating a platinum-rhodium alloy coating

摘要

The present invention provides a process of electroplating a platinum- rhodium alloy coating of predetermined composition and predetermined thickness on a metal substrate. The composition is substantially uniform throughout the electrodeposited coating. The process includes the steps of electrolytically dissolving an anode made of platinum or rhodium into a molten cyanide bath to prepare separately a platinum bath and a rhodium bath, forming a mixed bath having a predetermined ratio of platinum to rhodium from the separate platinum and rhodium baths, and electroplating platinum and rhodium onto a metal substrate, using a predetermined electrical charge and alternating a platinum anode with a rhodium anode, while monitoring and controlling the deposition potential of the metal substrate. This coating substantially corresponds in composition to the composition of the mixed bath. The process is carried out in a dry, inert gas environment. The molten cyanide bath is moisture-free, and there is immersed in this bath a selective ion transport membrane, such as a Pyrex, that maintains the cathode in a moisture-free cyanide bath separate from the bath in which the anode is immersed. Also provided is a process wherein the electroplating step is followed by an alloy electrodissolution step.