Study On Preparation Of Sm₂Fe₁₇N₃ Permanent Magnet Materials By Reduction Diffusion

The motor drives the magnet to rotate in the high temperature magnetic pump,achieving absolute sealing and zero leakage,which is of great significance to the petrochemical and petroleum refining industry.The magnetic drive device is key to the whole system and required to work stably in a high temperature environment above 150 ℃.At present,the permanent magnet materials including SmCo and NdDyFeB magnets are widely applied in the magnetic pump.However,SmCo magnets contain a large amount of strategic element Co which is high cost.Furthermore,the heavy rare earth element Dy is necessary for improving the high tempereature performace of NdDyFeB magnet,which also contain the scarce rare earth resource Nd.Therefore,it is of great significance to develop a new high-temperature permanent magnet material that does not require the addition of Dy,Nd,and Co elements to replace NdFeB and SmCo magnets.Sm2Fe17N3 has excellent intrinsic magnetic properties,expected to be used as a magnetic raw material in magnetic pumps working at high temperatures.The utilization of Sm2Fe17N3 also contributes to the efficient and balanced development of rare earth resources.In this research,the Sm2Fe17N3 permanent magnet materials is prepared by reduction diffusion method.The research contains the following aspects:The polyhedral single-crystal Fe3O4 particles with an average particle size of 0.44±0.18μm were prepared by an inexpensive Fe（Ⅱ）solution and Cu（Ⅱ）ions as catalyst under hydrothermal conditions at 200 ℃ for 1.5 h,the saturation magnetization Ms is 85 emu·g^-1.And the uniformly dispersed Sm（OH）3 colloid is directly attached to the surface of Fe3O4particles by precipitation method,thus realizeing magnetic separation.After reduction treatment at 600 ℃ for 4 h in a 10%H2/Ar atmosphere,and then a micro-oxidation treatment at 600 ℃ for 1 h in an Ar atmosphere,a stable submicron Fe@SmFeO3composite can be obtained in the atmospheric atmosphere.Under the condition of Fe/Sm≥7.5（Fe/Sm is the atomic ratio）,using metal Ca particles as reducing agent,the Sm2Fe17 particles with particle size between 0.69μm and 0.51μm were successfully obtained by reducing and diffusing in Ar environment at 900 ℃ for 1 h.According to the relationship between Fe/Sm ratio and the particle size of elemental Fe particles and Sm2Fe17 particles,it is found that the increase of Sm input amount will lead to the increase of the particle size of Sm2Fe17 particles.By tracing back the morphological changes of the samples at each treatment stage,it is believed that this phenomenon is caused by the generated Sm2Fe17 particles engulf each other and grow up,which resulting from the random diffusion of the reduced Sm elements to the surrounding Fe particles during the reduction diffusion treatment.Fe/Sm ratio has an important influence on the microstructure and properties of Sm2Fe17N3.When Fe/Sm=8.0,N2 was used as nitrogen source for nitridation at 420 ℃ for 10 h to obtain high purity phase spherical Sm2.03Fe17.00N2.40 with an average particle size of 1.22μm,but some particles are compacted.Its Ms and Hcj are 128 emu·g^-1 and 7609 Oe,respectively.In addition,the nitridation time of 16 h will cause the decomposition of Sm2Fe17N3 to formα-Fe soft magnetic phase.When Sm/Fe=8.5,the Sm input amount is consistent with the theoretical amount ratio,α-Fe is precipitated in the sample,resulting in a decrease in coercivity to 3261Oe,While Sm/Fe=7.5,due to the existence of Sm-rich phase,Ms and Hcj,also decrease to 116emu·g^-1 and 4000 Oe.