Sol (TiO2) Enhanced Nanocomposite Silver Coatings by Electroplating

Abstract

Electroplating as a surface treatment technology can significantly improve the properties of working parts and components which has been widely applied in a variety of technical fields. Recently this surface treatment technology has been developed to synthesize nanocomposite coatings. The nanocomposite coatings show a significantly improved mechanical properties due to the second-phase dispersed nanoparticles in the coating matrix. However, it is hard to realize a good suspension of solid nano-sized particles in a plating solution and good dispersion of nano-sized particles in the composite coatings because of the large surface energy of nano-particles. The traditional methods such as magnetic agitation, air injection, and ultrasonic vibration are always difficult to fully prevent agglomeration of nano-sized particles as the surface effect. To achieve a good dispersion of the nanoparticles in composite coatings, sol-gel enhanced electroplating is developed at the University of Auckland and intensively investigated. The aim of this research is to study the electroplating of sol enhanced Ag/TiO2 composite coatings. In the present thesis, TiO2 solid particles and a transparent TiO2 sol was added into a traditional cyanide silver electroplating electrolyte in order to prepare two different types of composite coatings. The research was started with an electroplating of pure silver coatings from traditional cyanide bath. Then investigations were carried out on the solid powder enhanced composite coatings and sol-enhanced composite coatings focused on the effect of the powder and sol concentration. The microstructure, mechanical properties, electrical properties as well as colour difference of the composite coating were investigated in the research. Both of the sol and powder enhanced electroplating successfully added dispersed TiO2 nanoparticles into the Ag coating matrix and improved the mechanical properties compared to the pure silver coating. The sol enhanced nanocomposite coatings shows better dispersion and mechanical properties.