Study On The Preparation And The Properties Of Silane Coating On NdFeB Magnets

Sintered NdFe B magnet with excellent magnetic properties has been widely used in each field of national economy since the advent of NdFe B magnet.However,the poor corrosion resistance of NdFeB magnet limits its further development in application fields.Therefore,a protective coating on the surface of sintered NdFeB magnetis required for improving the corrosion resistance of NdFeB magnets.Herein,silanization technique was adopted for NdFe B surface protection,silane conversion film was successfully prepared on the surface of NdFeB magnet,thus developping new type of environment-friendly temporary protective measurefor the NdFeB surface protection.Silane conversion films on the surface of of NdFeB magnet were prepared using dip-coating technique,and the corrosion resistance was studied by neutral salt spray test.Then,the orthogonal test was used to optimize the parameters of silane hydrolysis and film formation.The results showed that the optimum process parameters of silane hydrolysis was as follows: the concentration of silane coupling agent,ethanol water ratio,hydrolysis temperature,hydrolysis time and pH value are150 ml/L,80:20,30?,24 h and 11,respectively.The optimum parameters of silane film formation was that dip-coating for 2 min,prebaking at 80? for 15 min,curing at180? for 1.5h.The NdFeB magnets coated with silane conversion film which was prepared with optimized parameters show superior corrosion resistance yet poor mechanical properties.In order to further improve the mechanical properties and corrosion resistance of silane conversion film,CeO₂/silane composite film was prepared by doping CeO₂ nanoparticles in the dip-coating solution.The corrosion resistance of the prepared films was studied by neutral salt spray and potentiodynamic polarization tests.The binding force between the NdFe B substrate and the films as well as the microhardness of CeO₂/silane films were measured by tensile testing and microhardness tester respectively.The results showed that the CeO₂/silane composite films coated on the surface of NdFeB magnet show much better corrosion resistance and mechanical properties than that of silane conversion film.The corrosion mechanism of silane conversion films and CeO₂/silane composite films prepared on the surface of NdFeB magnet was systematically studied,and thecorresponding corrosion model was initially established as well.This work will provide technical support for the sintered NdFe B surface protection by silanization treatment.