Preparation And Corrosion Resistance Of NiP/TiO₂ Composite Film On NdFeB Magnets And Remove Ni～(2+) From Spent Electroless NiP Plating Bath

NdFeB magnet have been widely used in electronic industries and apparatus industries, etc, because of their excellent magnetic properties, comparatively low price and a store of raw material. But NdFeB magnet is unstable, and they are easy to be oxidated in common atmosphere, especially to be highly susceptible to corrosion in the humid environments, so its applied field is restricted. To resolve the problem, a NiP/TiO2 composite film, coating on NdFeB magnet, has been studied. On the other hand, there is some residual nickel ion with higher concentration in the spent electroless Ni-P plating solution. The nickel ion will cause the serious pollution of the water resource, and do harmful to the human health. Removal of the Ni ion in the spent electroless Ni-P plating bath has been studied in the paper.The pretreatment teghnology of Ni-P electroless plating is confirmed, and the process of the electroless plating has been optimized by the orthogonality experiment. The preparation of NiP/TiO2 composite film has been investigated. Corrosion resistance of the NiP coating and NiP/TiO2 composite film have been characterized by the polarization resistance, polarization curve measurements. The structures of NiP coating and NiP/TiO2 composite film have been studied by XRD, the surface photographs and the chemical components of them have been investigated by SEM-EDS. Results show that the Ni-P coating and NiP/TiO2 composite film has a good corrosion resistance in 0.5 mol·L-1 H2SO4 solution and 0.5 mol·L-1 NaCl solution.In the spent electroless Ni-P plating bath, most of the nickle ion are presents with the complexing existence, so the chemical oxidant is used to destory the complexation system, then pH of the bath is adjusted to 13.20 by NaOH solution.The removal rate of Ni ion can reach 95%. But the residual concentration of Ni is still higher. An ion exchange resin is used to remove theresidual Ni ion, and the concentration of Ni in the spent bath decreased below to 20 mg·L-1.The problems should be resolved in the next study are: (1) optimizing the preparation of NiP/TiO2 composite film with a better corrosion resistance property; (2) study of the new technology for Ni ion removal and reuse.