Microstructure and corrosive property of Ni-P/nano-CeO2 coating electrolessly prepared in acidic condition

Abstract

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), transmission electronic microscopy (TEM) and differential scanning calorimeter (DSC) were used to examine surface morphology and microstructure of the coating. Aqueous corrosion was done in 3%NaCl+5%H2SO4 solution and high temperature oxidation was done at 750 °C in air. 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. At high temperature, Ni3P precipitation and Ni crystallization took place in both coatings at different temperatures. Aqueous corrosion property and high temperature oxidation property of the composite coating were remarkably improved due to the coating’s microstructure change and the rare earth doping effect. During the co-deposition process, some Cen+(n=3, 4) ions may be adsorbed to metal/solution interface and hinder nickel deposition. Ni-P/CeO2 coating’s perfect amorphous structure results from the hindered crystal- typed deposition of nickel and the promoted deposition of phosphorous.