FORMATION OF COBALT CYANIDE COMPLEXES IN HARD ACID GOLD BATHS

The release of free cyanide ions during electrolysis of hard acid gold baths can lead to substantial ''lock-up'' of transition metals added as co-depositing elements. This results in softer, duller gold deposit s which are unlikely to meet performance specifications. In order to r estore deposit properties, drastic action may be necessary. Whilst the phenomenon is well known amongst academia, there appears to have been little ''translation'' into practical guidelines for preventative mea sures and controls. These complexes are most often encountered in soph isticated plating plants. (e.g. reel-to-reel spot platers), where prac tical chemistry is subordinate to engineering and production demands. Cobalt systems are most affected. The formation mechanism and stabilit y of the complex, and remedial and preventative actions, are discussed .