Progress in Surface Modification Technology and Application of Nd-Fe-B Powder
The Nd-Fe-B magnets are indispensable components for modern technologies,which are widely used in numerous devices such as electric motors,hybrid vehicles and wind generators due to their high coercivity(Hcj),high remanence(Br)and high maximum magnetic energy product((BH)max).Although Nd-Fe-B magnet is the most widely used permanent magnetic material at present,it still has many shortcomings,such as poor thermal stability,easy oxidation and corrosion,and low resistivity,which makes the application of Nd-Fe-B magnets limited.The development of bulk Nd-Fe-B magnets is usually based on magnetic powder as a precursor,followed by sintered,hot-pressed/hot-deformed or bonded magnets.The surface modification of Nd-Fe-B magnetic powder before the preparation of bulk Nd-Fe-B magnets is an effective means to solve the existing shortcomings of Nd-Fe-B magnets.However,the research on the surface modification of Nd-Fe-B magnetic powder is scattered and lacks systematic and detailed summary.Based on this,the work aims to introduce the preparation process of sintered Nd-Fe-B magnets,bonded Nd-Fe-B magnets,hot-pressed/hot-deformed Nd-Fe-B magnets and the preparation methods of different types of Nd-Fe-B magnetic powders.The mechanism of surface modification by deposition coating treatment,pickling activation passivation treatment and silane coupling agent treatment was summarized.Deposition coating treatment could form a dense and good protective film on the surface of Nd-Fe-B magnetic powder.Pickling activation passivation treatment could activate the surface morphology of Nd-Fe-B magnetic powder.Silane coupling agent treatment could form an organic polymer layer on the surface of Nd-Fe-B magnetic powder.Secondly,the effects of surface modification techniques such as deposition coating treatment,pickling activation passivation treatment and silane coupling agent treatment on the magnetic properties,oxidation resistance,corrosion resistance and resistivity of Nd-Fe-B magnets were emphasized.It was pointed out that different surface modification technologies were suitable for different types of Nd-Fe-B magnets.The Nd-Fe-B magnet prepared by Nd-Fe-B magnetic powder obtained by deposition coating treatment had a significant improvement in oxidation resistance,corrosion resistance and resistivity.The Nd-Fe-B magnet prepared by Nd-Fe-B magnetic powder obtained by pickling activation passivation treatment had a significant improvement in oxidation resistance and corrosion resistance.Compared with deposition coating treatment technology and pickling activation passivation treatment,silane coupling treatment mainly adopted organic silane solution to modify the surface of Nd-Fe-B magnetic powder,forming a molecular layer on the surface of magnetic powder,so as to change the surface morphology of Nd-Fe-B magnetic powder.The Nd-Fe-B magnetic powder treated with organic silane solution is suitable for bonding Nd-Fe-B magnets,mainly due to the low melting point of the organic polymer layer on the surface of the modified Nd-Fe-B magnetic powder,which is not suitable for high temperature and high pressure molding.Finally,the surface modification technology of Nd-Fe-B magnetic powder is summarized and prospected.It is extremely important to explore different surface modification methods and promote practical applications.For example,the development of modifiers with excellent and stable properties,the exploration of modification technology matching with mainstream molding methods,and the customization of magnetic powder surface modification methods corresponding to the specific application of magnets will be the development direction of powder surface modification technology.
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维普
