Ce在镧系元素中是具有特殊性质的一员,其根源在于它的混合价特性.在Ce2 Fe14 B化合物中,Ce表现出强烈的+4价倾向,不仅自身4 f电子缺失无法贡献稀土离子磁性,而且离子半径过小导致Fe-Fe间距缩减,使Ce2 Fe14 B居里温度和饱和磁极化强度都以较大的幅度地下降.另外,在Ce-Fe-B三元合金中,Ce倾向于生成Laves相CeFe2,而非富稀土低熔点晶界浸润相,不能在烧结磁体中产生使主相晶粒退磁耦合的矫顽力机制,烧结Ce-Fe-B难以实现高矫顽力.尽管如此,Ce2 Fe14 B仍具有优良的内禀磁性,通过快淬方法可制备出性能适中的(Ce,Nd)-Fe-B各向同性磁粉,而通过贫Ce富Nd和贫Nd富Ce双合金或双主相烧结的方法,用富Nd相承担分割主相晶粒提高矫顽力的功能,也实现了高性价比(Ce,Nd)-Fe-B烧结磁体的商品化.综合阐述了元素Ce影响钕铁硼磁体内禀磁性和矫顽力方面的研究工作.
Cerium is a very special element in Lanthanide, originating from its mixed valence characteristics. Ce exists in Ce2 Fe14 B as Ce4+ ion. The lack of 4f electron leads Ce4+ to make no contribution to magnetism. Small ion radius shrinks the Fe-Fe distances and decreases the Curie temperature and saturation polarization of Ce2 Fe14 B. In addition, it is in favor of CeFe2 Laves phase instead of Ce-rich phase to magnetically decouple Ce2 Fe14 B grains. Sintered Ce-Fe-B magnet has very poor coercivity. Rapidly quenched isotropic ( Ce, Nd)-Fe-B powder can realize reasonable HcJ for certain applications. By dual-alloy or dual-main-phase techniques, using Ce-rich/Nd-lean alloy and Nd-rich/Ce-lean alloy as starting materials, sintered ( Ce, Nd)-Fe-B magnet is commercialized with high ratio of performance to cost. The key point is to let Nd-rich phase decouple ( Ce, Nd) 2 Fe14 B grains. This article reviews the effects of Cerium on the intrinsic and extrinsic magnetic properties of Nd-Fe-B permancent magnets.
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