Microstructure and corrosion behavior of electroless deposited Ni–P/CeO2 coating

Electroless Ni–P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) spectrometer were used to examine surface morphology and structure of the as-plated coating. Differential scanning calorimeter (DSC) and transmission electronic microscopy (TEM) were used to study the coating’s phase change at high temperature. The coating’s corrosive behavior in 3%NaCl + 5%H2SO4 solution was also investigated. The results showed that Ni–P coating had partial amorphous structure mixed with nano-crystals, while the Ni–P/CeO2 coating had perfect amorphous structure. In high-temperature condition, Ni3P precipitation and Ni crystallization took place in both coatings but at different temperatures, while the Ni–P/CeO2 coating had sintered phase of NiCe2O4 spinels. The anti-corrosion property was better in the CeO2-containing coating, and this was due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart. Ni–P/CeO2 coating’s pure amorphous structure was the result of Ni’s hindered crystal-typed deposition and P’s promoted deposition.