Structural characterization and corrosive property of Ni-P/CeO 2 composite coating

Abstract

Electroless Ni-P/nano-CeO 2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO 2-free counterpart. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), X-ray diffraction spectrometer (XRD), and differential scanning calorimeter (DSC) were used to examine surface morphology and microstructure of the coating. Corrosive investigation was carried out in 3%NaCl+5%H 2SO 4 solution. The results showed that Ni-P coating had partial amorphous structure mixed with nanocrystals, whereas the Ni-P/CeO 2 coating had perfect amorphous structure. In high temperature condition, Ni 3P precipitation and Ni crystallization occurred in both coatings but at different temperatures, whereas the Ni-P/CeO 2 coating had sintered phase of NiCe 2O 4 spinels. The anticorrosion property and passivity were improved in the CeO 2-containing coating due to its less liability to undergo local-cell corrosion than its CeO 2-free counterpart. During the co-deposition process, some Ce n+ ( n=3, 4) ions may be adsorbed to the metal/solution interface, hinder nickel's crystal-typed deposition and promote phosphorous deposition. The nano-CeO 2 doping finally resulted in the coating' perfect amorphous structure and good anti-corrosive property.