氧化钐直接高温电解制备Sm2Fe17合金方法的研究

Rare-earth resource in China has abundant reserves, it has been exploited and utilized to contribute not only economic development but also has the far-reaching strategic significance. Recently the rare-earth product to export in the world has absolute advantage, but lots of rare-earth products to import need, that shows our preparation technology of the rare-earth product need is urgent to improved. In this project, a method of Sm2Fe17 alloy electrolyzed directly from samarium oxides is proposed according to thermodynamic principle, solving a bottleneck problem for preparation of Sm2Fe17Nx permanent magnet. In the research process, temperature from 1014oC to 1285oC is controlled for crystallization of Sm-Fe alloy with homogeneous phase. A mixed electrolyte of molten salt and molten slag is used to improve the properties of physical chemistry for high-temperature electrolysis. The electrode reaction and the coupling effect with the iron-cathode are investigated to reveal the formation mechanism of Sm-Fe alloy. The reaction kinetics of liquid-solid phases is researched to understand the rate-controlling step in the alloying process. Influences of ion-cycles and electronic conduction between anode and cathode in electrolyte are eliminated by a double-cathode to solve a common problem existing in electrolysis of multi-valence oxides. Moreover, the interaction of multiple factors is determined on combination of the above results to establish a new method of high-temperature electrolysis for preparation of Sm2Fe17 alloy, enhancing the rate and current efficiency of electrolysis, and developing of high-temperature electrolytic theory.

我国稀土资源储量丰富，它的开发和利用，不仅关乎经济发展，而且具有深远的战略意义。近年来，尽管稀土产品出口量在世界上已占绝对优势，但还有相当比例需要进口，反映了我国的稀土产品制备技术还亟待提高。本项目，根据热力学原理，提出氧化钐直接电解制备Sm2Fe17合金方法，解决制备Sm2Fe17Nx永磁材料中遇到的"瓶径"问题。研究过程，考虑控制合金的单一相析出，在1014oC -1285oC范围进行；探讨熔盐-熔渣混合电解质的使用，提高高温电解的物理化学性能；研究不同阴极上的电极反应及其耦合作用，揭示Sm-Fe合金形成规律；通过液-固相反应动力学研究，明确合金化过程的控速环节；研究双阴极抑制两极间离子循环等机理，解决变价氧化物电解中存在的共性问题。进一步，考虑多因素的交互作用，提出高温电解制备Sm2Fe17合金方法，以期提高电解速率和电流效率，发展电解理论。

Sm2Fe17Nx被誉为第四代永磁材料，其性能优异，具有较大的发展潜力。作为前驱体，Sm2Fe17制备有熔体淬冷法、机械合金法和还原扩散法，但都难获得Sm2Fe17单一相。本项目，根据Sm-Fe相图从理论上解决了这个问题，提出熔盐电解制备方法，经CaF2-CaCl2-SmCl3和LiF-CaF2-SmF3熔盐电解实验验证了方法的可行性，并获得了重要的基础数据，其创新性结果如下：.（I）弄清了熔盐电解制备Sm2Fe17关键参数。摩尔比4:6时CaF2-CaCl2熔盐Sm2O3溶解度最大（1100oC时10.66mg/g），提高温度有利于改善Sm2O3溶解动力学条件，获得了CaCl2-CaF2-SmCl3(1100oC)和LiF-CaF2-SmCl3(1160oC)熔盐Sm3+扩散系数分别为1.651×10-5 cm2/s和8.52×10-5 cm2/s。.（II）揭示了阴极上Sm离子还原的电化学规律。CaF2-CaCl2和LiF-CaF2熔盐电势窗分别为-1.30V（1100oC）和-1.18V（1160oC） vs Cr/Cr2O3，相对应的铁电极上Sm3++eSm2+和Sm2++2e Sm(Fe)开始还原电势分别为-0.26V和-1.18V与-0.37V和-0.77V vs Cr/Cr2O3，发现Sm3++e=Sm2+过程是可逆的、由Sm3+扩散控速。.（III）明确了Sm(l)+Fe(s)Sm2Fe17过程属于扩散控速，发现Sm2Fe17生成与Sm液相中Fe溶解同时进行，提出熔盐电解“上阳极-下阴极空间配置” 制备Sm2Fe17合金的关键技术。.（IV）利用CaF2-CaCl-SmCl3熔盐，验证了方法制备Sm2Fe17合金的可行性，电流效率达80%，提出了一种氧化钐卤化-熔盐电解制备单一相Sm2Fe17合金方法。