Crystallization And Nitride Behaviors During The Preparation Of TbCu₇-type SmFe₉N_X Magnetic Powder

The TbCu7-type SmFe9Nx magnetic powder have high magnetic performance, good heat-resisting performance, low cost, and can be prepared into a complex magnet because of the isotropic characteristic. The excess rare earth samarium can be consumed to prepare the TbCu7-type SmFe9Nx magnetic powder, which can help balance the use of rare earth resources. Therefore, it has a very important significance for the development of new permanent magnetic materials to study the TbCu7-type SmFe9Nx magnetic powder.In this paper, the TbCu7-type SmFe9alloy powder was analyzed by DTA, oxygen and nitrogen content, magnetism testing results, XRD, VSM and so on after crystallization and nitride treatment, the relationship between the crystallization temperature, crystallization time, nitriding temperature, nitriding time and particle size of the SmFe9alloy powder with the magnetic properties was investigated. The diffusion behavior of the nitrogen atoms during the preparation of TbCu7-type SmFe9Nx isotropic bonded magnetic powder was studied, and the distribution of nitrogen atoms in the SmFe9alloy particles and the relationship between the distribution with diffusion temperature, diffusion time and particle size were calculated and discussed by Fick second diffusion law. Through the research, conclusion was been made as follows:(1) The nitriding effect has been greatly improved after crystallization heat treatment, nitrogen content and magnetic properties were increased with the rise of crystallization temperature and crystallization time, when the crystallization temperature exceeded750℃or crystallization time exceeded45min, nitrogen content and magnetic properties upgrading was no longer apparent. Based on experimental results, the magnetic properties of the SmFe9alloy was highest after crystallization treatment at750℃for60min and nitride treatment at same condition;(2) The SmFe9Nx interstitial compounds was formed, when the nitrogen atoms went into the crystal lattice of1:7phase after nitride treatment, the magnetic properties was greatly improved, and the curie temperature has increased about300℃. The nitriding temperature, nitriding time and particle size of the SmFe9alloy powder influenced nitriding efficiency. It has been found experimentally that nitrogen content increased with the rise of the nitriding temperature, but the SmFe9Nx would decompose if the nitriding temperature was too high; Longer nitriding time can increase the nitrogen content, however, nitrogen content upgrading was no longer apparent when the nitride time was more than11h. Nitrogen content increased with the SmFe9alloy powder particle size decreased, but the SmFe9alloy powder would be oxidized if the particle size was too small, which would affect the nitriding process and the final magnetic particle performance. Based on experimental results, the magnetic properties of SmFe9alloy powder which particle size was about80μm was highest after nitriding treatment at440℃for8h;(3) The nitrogen atom diffusion into its internal from SmFeg particle surface in nitridation process, which followed the Fick second diffusion law. Through the thermal magnetic curve of the SmFe9Nx and the diffusion theory calculation, the nitrogen content in SmFeg internal was not uniform distribution, and the closer particle center, the lower the nitrogen content. The values of the diffusion frequency factor (Do=9.565×10-4m2·s-1) and the diffusion activation energy (Q=147.282kJ·mol-1) for the nitrogen atoms diffusion in SmFeg particle were obtained through the computation, and the diffusion coefficient of the nitrogen atoms diffusion in the SmFe9alloy increased with the rise of the nitriding temperature.