Pulse Electroplated Sn-ZnO And Sn-Fe₂O₃ Nano-Composite Coatings With Ultrasonic Field Assisted

In this paper, Sn-ZnO and Sn-Fe2O3 composite coatings were fabricated by pulse nano-composite plating technique in the ultrasonic field. The properties of composite coatings, such as the surface morphologies and microstructures, microhardness, corrosion resistance, photocatalysis, were characterized and analyzed by scanning electron microscopy (SEM), micro hardness tester, UV-visible spectrophotometer, respectively. Thereby determined the influences of the ultrasonic field, type of the nano-particles, electroplating process parameters, heat treatment to the coating. The main works completed and conclusions are presented as follows:Firstly, by using the ultrasound, we obtained higher porosity and worse compact-ability Sn-ZnO composite coating. However, in the case of Sn-Fe2O3 composite coating, we obtained different results with lower porosity, better compact-ability and refinement of the grain.Secondly, Sn-ZnO composite coating with irregular whisker-shape grains can be obtained by pulse electroplating in ultrasonic field. Compared with constant current electroplating, Sn-Fe2O3 composite coating by pulse electroplating exhibited a more uniform grain size distribution, better compact-ability and better surface roughness.Thirdly, Sn-ZnO composite coating prepared in a lower pulse average current density shown smaller grain size, more uniform grain distribution. However, in the case of Sn-Fe2O3 composite coating, we obtained different results with a more uniform grain distribution, better compact-ability and much better surface.Fourthly, after a time period of heat treatment, the grains of the Sn-ZnO composite coating changed from whisker-shape to grain-shape with the diameter slightly increased, and a better compact-ability and low pore ratio of the coating were achieved. We also obtained the similar results from the case of Sn-Fe2O3 composite coating after a time period heat treatment, and a better surface smoothness was also achieved.Fifthly, in a 5% H2SO4 solution, Sn-ZnO composite coating prepared by pulse electroplating in ultrasonic field exhibits much worse erosion resistance than that of Sn coating prepared by pulse electroplating without ultrasonic field in the same average current density. However, in the case of Sn-Fe2O3 and Sn composite coating prepared by pulse electroplating in the same average current density in ultrasonic field, Sn-Fe2O3 composite coating shown much better corrosion resistance than that of Sn coating in a 5% H2SO4 solution. Moreever, Sn-Fe2O3 composite coating prepared in a lower average current density exhibited better corrosion resistance.Sixthly, Sn-Fe2O3 composite coating prepared by pulse electroplating in ultrasonic field exhibits much higher microhardness than Sn coating prepared by pulse electroplating in the same average current density. With decrease of average current density during the pulse electroplating process, Sn-Fe2O3 composite coating exhibit higher microhardness.Seventhly, the photocatalysis of the particles on Sn-ZnO nanocomposite coating prepared by pulse electroplating in ultrasonic field are stronger than that of Sn-Fe2O3 nanocomposite coating by pulse electroplating without ultrasonic field. Moreover, the photocatalysis of Sn-ZnO composite coating increased with decreasing average current densities.