THE EFFECT OF SEVERAL BENZYL ALCOHOLS AND ELECTRON BRIDGING ANIONS ONTHE CURRENT EFFICIENCY FOR DEPOSITION OF CADMIUM

Because of the ability of millimolar concentrations of substituted ben zyl alcohols to block hydrogen evolution and to form complexes with th e cadmium ions, their addition to cadmium sulfate and chloride plating baths increased the current efficiency for depositing cadmium. In sul fate baths there was generally a linear correlation between the concen tration of the cadmium-alcohol complex and the current efficiency. In the cadmium-chloride system, in which the alcohol could not displace c hloride and form a complex, the current efficiency was primarily relat ed to the blocking of hydrogen evolution. Addition of electron bridgin g anions also catalyzes the deposition of cadmium, and this mechanism of catalysis does not change upon addition of the alcohol. The catalys is decreases in a very regular fashion as the size of the bridging ani on increases, indicating that the electron bridging occurred through h oles in the alcohol film. Addition of millimolar nonbridging strong co mplexing agents inhibits metal deposition and decreases current effici ency Addition of millimolar surfactants increases the current efficien cy by blocking hydrogen evolution.