高性能Sm2Fe17N x 粉体制备的研究进展

新能源汽车的高速发展,需要能稳定工作在120℃~200℃温度区间的永磁材料。居里温度为476℃、各向异性场为14.7 T的Sm₂Fe₁₇N₃,具有优良的本征磁性能,可应用在这个温度区间。为了提高Sm₂Fe₁₇N₃粉体的磁性能,必须将颗粒的粒径减小到临界单畴尺寸以实现高各向异性场；同时,还要避免颗粒尺寸减小产生的表面氧化,以保证高剩磁和最大磁能积。粉体破碎、机械合金化、甩带、薄带连铸、还原扩散以及表面镀覆等多种制备工艺,可用于制备高性能Sm₂Fe₁₇N₃。目前,实验室制备的Sm₂Fe₁₇N₃粉体的矫顽力和最大磁能积已经达到28.1 kOe和43.6 MGOe。本文评述近年来Sm₂Fe₁₇N₃粉体制备的研究成果,包括对制备机理的系统总结并提出仍待解决的关键问题：Sm₂Fe₁₇N₃粉体的矫顽力、剩磁等与其颗粒尺寸的量化规律以及与颗粒磁畴结构的关联机制；对NH₃/H₂混合气体中H₂对提高氮化效率的作用机制仍需探索；进一步开发在低氧环境下的颗粒粒径均匀化、控制形貌的二次破碎技术；对于还原扩散法,开发适合规模化应用的新前驱体及其制备方法以及快速去除钙副产物的水洗技术等。

Recent Development for Preparation Processes of Sm2Fe17N x Powders with High Magnetic Properties

The rapid development of new energy vehicles requires permanent magnet materials that can work stably in the temperature range of 120℃~200℃. Sm₂Fe₁₇N₃ with Curie temperature of 476℃ and anisotropic field of 14.7 T has excellent intrinsic magnetic properties, and can be used in this temperature range. In order to improve the magnetic properties of Sm₂Fe₁₇N₃ powder, the particle size of which should be reduced to the critical size close to a single domain, so that to gain high anisotropic field; Meanwhile, surface oxidation caused by particle size reduction should be avoided to ensure high remanence magnetism and maximum magnetic energy product. High performance Sm₂Fe₁₇N₃ can be prepared by powder crushing, mechanical alloying, strip casting, thin strip continuous casting, reduction diffusion and surface plating. At the present, the coercivity and maximum magnetic energy product of Sm₂Fe₁₇N₃ powder prepared in laboratory have reached 28.1 kOe and 43.6 MGOe respectively. In this paper, the research results on the preparation of Sm₂Fe₁₇N₃ powders in recent years are reviewed, including preparation methods and the relevant mechanism, and key problems that remain to be solved, namely the relation of the coercivity and remanence of Sm₂Fe₁₇N₃ powder with the particle size, as well as with the particle magnetic domain structure；the mechanism related with the enhanced effect H₂ within the gas mixture NH₃/H₂ on the nitriding efficiency of the powder still needs to be revealed; further the secondary crushing technique in low oxygen pressures, which can prepare particles with uniform distribution of particle size, while adjust their morphology, remains to be developed; for the present reduction diffusion method, new precursors, and their preparation methods suitable for massive production, and water washing technology for rapid removal of calcium by-products were also needed to develop.