Role of nano TiO2 and nano ZnO particles on enhancing the electrochemical and mechanical properties of electrochemically deposited phosphate coatings

Abstract

In this work, nanocrystalline phosphate coatings are systematically produced on low carbon steel with different preparation modalities using nano TiO2 and nano ZnO particles. For the sake of comparison, normal zinc phosphate coatings are also produced. All the phosphate coated samples are subjected to the thermal annealing at 100, 200, 300 and 400 °C for 1 h in argon atmosphere. Our results through combined electrochemical characterization and nanoindentation experiments revealed that nano TiO2 and nano ZnO particles act as a sealing agent, and therefore prevent crack propagation which enhances the electrochemical and mechanical properties of these coatings. Annealing treatment, along with the recrystallization of metallic matrix, promotes the corrosion resistance of all the phosphate coatings. In fact, among all the classes of coatings, annealed samples at 400 °C exhibit higher nanomechanical properties and lower corrosion rates. The results also invoked that nano TiO2 phosphate behaviour prevails over other two. Therefore, this dominant behaviour is mostly due to the accumulation of hard Zn-P precipitates upon annealing which exfoliates the outermost layer and therefore exposing the underneath layer to corrosive media, eventually delaying the onsets of corrosion attack. Our results highlight, for the first time, the ample avenues of enhancement in the electrochemical performance as well as nanomechanical properties of electrochemically deposited phosphate coatings using the incorporation of nano TiO2 and nano ZnO particles in water based phosphate bath followed by subsequent cost effective annealing treatment.