Study On Advanced Green Anticorrosive Coating For NdFeB Rare Earth Permanent Magnet

NdFeB rare-earth permanent magnet materials with superior high magnetic performances have been widely applied in the fields of electronics,information technology,motor,communications engineer,wind power and so on.However,NdFeB magnets perform a poor corrosion resistance,which has greatly limited the magnets applications.Normally,electroplating is a traditional method to protect NdFeB permanent magnet corrosion.The electroplating industry production process is accompanied by a large number of toxic and harmful liquid wastes.It doesn't only pollute the environment but also harms human health.The electroplating method doesn't meet the concept of green environmental protection in our country.Therefore,a new method to get an efficient and green coating is necessary.In this work,we proposed a new coating method.This method introduces Dacromet technology into NdFeB corrosion protection.And we also removed chromium from traditional Dacromet technology.The new coating method includes flaky zinc powder,aluminum powder,binder,organic solvents and other sing redients.The coating liquid was coated on the surface of NdFeB magnets,and then the coated magnets were heated to solidify the coating layer.Finally,the efficient protecting coating layer composed of zinc,aluminum flakes,and binder was obtained.Based on many experiments,the results are shown as follows.Firstly,the coating formula was determined according to the properties of the three different types of binders(phenolic resin,epoxy resin and silane coupling agent).The coating layer by using silane coupling agent binder presents good properties of corrosion potential,the minimum corrosion current and the highest resistance,salt spray test for 480 h,heat resistance for 36 h.Thesilane coupling agent is a optimal binder for coating.Secondly,the coating procedures of sintering have been studied.Silane layer surface could form a dense and excellent corrosion resistance,when the sintering temperature was at 300?,the coating layer perform a very perfect anticorrosion properties.The NSS test could take about 600 h,PCT test reached to 48 h.The new type of coating layer has better performance than that of traditional electroplating anticorrosion of Ni-Cu-Ni.We wish this new type of coating technology can take place of traditional electroplating technology.Finally,we tried to add different content of TiO2 nanoparticles in the new anticorrosive coating.With the increase of the content of TiO2 nanoparticles,the corrosion resistance of the coating improved gradually.When the TiO2 nanoparticle content was 3wt.%,the coating resistance to NSS test was 480 h and the resistance to PCT test was 48 h.The nanometer scale powder can fill the gap of the coating to improve the corrosion resistance.But when the non-conducting TiO2 nanoparticles are excessive,the particles exist in between flake zinc and aluminum will destroy the protective effect of Al powder Zn powder to form sacrificial protection of primary batteries in the process of electrochemical corrosion.