ELECTRODEPOSITION OF THIN PD-AG FILMS

Thin Pd-Ag layers were electroplated preferably on brass and on nickel substrates using a two-compartment cell separated by an anion exchange membrane. The weakly alkaline electrolyte contained glycine-glycinate as the major complexing agents. The plating experiments were usually carried out without stirring, at different potentials and temperatures and in the absence or in the presence of sodium benzaldehyde-2,4-disulphonate (BDS). The samples were characterized by scanning electron microscopy and light microscopy. Their compositions were determined analytically by the inductively coupled plasma technique. In addition, the film porosity was tested. Electrodeposition in almost limiting current conditions for both components and without simultaneous hydrogen evolution led to deposits with compositions being in good agreement with the molar metal ratio in the electrolyte (77:23). The best results were achieved between 0 and - 50 mV with respect to a reversible hydrogen electrode at 0-degrees-C in the presence of BDS. These deposits were bright, had good adherence and exhibited no pores at a film thickness of 1.2 mum. At too negative potentials, the deposits became black and powdery.