E. Rosolymou, S. Spanou, A. Karantonis, E.A. Pavlatou
Nano & Dispersion Coatings, European Interfinish (2015), 26-27 February, Politecnico di Milano, Italy (oral)
Tin-nickel alloys are widely known in industry and microelectronics due to their attractive features, such as resistance to corrosion, ductility and solderability. These alloys are nonallergic to skin. The non-allergic property allows it to replace the electroplated nickel on fasteners for garments. It finds application in replacing chromium in decorative and light engineering industries and in printed circuit boards as an etching resist. Tin-nickel alloys are ideal for fabrication of Li-ion batteries. In particular, the Sn-Ni electrode has high electrochemical capacity and delivers a steady capacity even after 100 charge-discharge cycles. The regulation of alloys structure has a significant practical importance. The possibility to obtain metastable phases by electroplating is well ascertained. In most cases, this fact is related to irreversibility of an alloy phase composition and microstructure. The electroplating is a prospective and economic way of Sn-Ni alloys production but it is rather difficult to obtain films with the desired chemical and phase composition. This work aims to correlate the observed structural characteristics of Sn-Ti coatings reinforced by TiO2 nanoparticles (i.e. chemical analysis of the alloy, percentage of the embedded nanoparticles in alloy matrix) with the type of applied current and the resulting mechanical and chemical properties. Under this framework, composite coatings of tin-nickel matrix enhanced by titania nano-particles were produced under direct (DC) and pulse current (PC) conditions. The electrodeposition was carried out from a chloride/fluoride electrolytic bath with constant temperature of approximately 70±1oC and pH 4.4. Additionally, tin-nickel pure coatings were also produced and characterized for comparison reasons. The influence of the variable electrolysis parameters (current density, frequency and duty cycle of pulses, load of particles in the bath) on the surface morphology, structure, mechanical and chemical (anticorrosive) and photocatalytic properties were examined. According to the experimental findings it is proven that the use of low current density in the bath favors increased incorporation percentage of titania nanoparticles and enhanced microhardness values. In general, the overall experimental data reveal that the proper selection of electrodeposition parameters could lead to the production of nano-structured tin-nickel matrix composites exhibiting enhanced mechanical and anticorrosive properties.