Environmentally friendly baths for Cu-Sn co-electrodeposition: cyanide-free aqueous bath and deep eutectic solvents

This thesis describes the work of my Ph.D studies in Industrial Engineering during past three years. It regards preparation of copper-tin alloys from green solvents for decorative purposes. Actual industrial process involves cyanide based complex bath in order to produce white bronze layers and they often contain lead as brightener and whitener. The aim of the thesis is to develop a more environmental friendly process for white bronze electrodeposition. Two different electrolytes were considered as eligible candidates: one involves a simple organic acid aqueous solution as bulk electrolyte, and the other one is a new deep eutectic solvent bath. The investigation of electrodeposition using methanesulfonic acid as complexing agent considered a commercial bath and its optimization in order to be used in the decorative industry. The focus of the study was on the optimization of deposition parameters and verification of bath and deposit stability which was very important from industrial point of view. Obvious improvements on deposits quality and bath stability can be realized by replacement on anode material and utilization of pulse current. Contrary to that, research on electrodeposition from deep eutectic system was quite new and few relevant studies can be referred especially in the field of alloys. As a result, this work started from deposition of single metal for better understanding of behaviors of mixtures between choline chloride and ethylene glycol or urea. Successful deposition of copper-tin alloys can be carried out under warmed conditions and variation on film composition can be controlled by changing concentrations of metallic salts in the bath. Pulse current acted as an effective tool to refine microstructure of deposits in a similar way as in aqueous solvents. Since no brightener was added, reduced luster was observed here and working mechanism of additives was found to be rather different from that in conventional baths. In summary, operation parameters including temperature, salt concentration, anode material and supporting electrolytes influence the resultant properties of deposits in great extent. Deposit quality from both solvents can be improved by using pulse current with proper frequency.