Oxidation behavior of the supercritical water on the ternary Ni-W-P coating

In this work, the Ni-W-P coating was deposited on the specimen surface and oxidation of supercritical water (SCWO) experimental rig was specially established. Meantime, the structure and composition of ternary Ni-W-P coating on the specimen surface were profoundly analyzed with scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). After SCWO, the surface of Ni-W-P coating is still dense and has non-observed exfoliation due to its protection. Amorphous Ni-W-P coating crystallizes to some extent. Wrapped W and P elements in nickel cell are released after SCWO, resulting in the formation of nickel oxide and tungsten oxide. But the diffusion of metal cations and the growth of oxides are the vital factors inhibiting the oxidation of SCW. There is no viewing boundary layer between the oxidized Ni-W-P coating and the substrate, as the interface between the substrate and the shallow layer has been fused due to the decomposition of amorphous nickel cell at high temperature. Moreover, fractal method was specially investigated to evaluate the SCWO resistance of Ni-W-P coating. It was found that with the increase of W content in the coating, the fractal dimension decreases. Thereupon the SCWO resistance and stability of Ni-W-P coating become worse. The results express that the fractal characterization of non-seriously oxidized Ni-W-P coating is approximately linear after SCWO. The ternary Ni-W-P coating with a certain component still has good SCWO resistance at high temperature and high pressure. The compactness of the coating surface can be excellent and the SCWO in the head of nickel furuncle can be effectively inhibited.