Purification of Rare Earth Metals by Advanced Electron Beam Floating Zone Melting Method

本文研究了用传统的高真空电子束浮区熔炼（EBFZM）技术和两种新型的先进EBFZM技术提纯钕和镧，去除其棒中的非金属和金属杂质。对于后者，在低压氢气氛（P <H2>=10 <-3>~ 10 μ <-5>Pa）和外加直流电流（500 ~ 1000 A/cm ~ 2）条件下进行EBFZM处理，发现常规EBFZM处理后，碳和硫的含量因区带通过而降低，而钕和镧的氧和氮含量几乎没有降低。通过蒸发，可以除去钙、镁等蒸气压比钕、镧高的金属杂质。虽然铁、硅和铜的还原不可能通过蒸发进行，但它们可以在区域通过期间重新分布。EBFZM后，Nd和La的剩余电阻率比增加，这是由于相应杂质减少的结果。另一方面，先进的EBFZM技术有望比传统技术更有效地减少Nd和La中的非金属杂质。然而，人们认识到，我们应该首先研究并找到先进EBFZM处理的稳定区熔化的良好条件，以利用其对稀土金属的净化作用。

Purification of neodymium and lanthanum, removal of non-metallic and metallic impurifies from their rods, has been examined by the conventional electron beam floating zone melting (EBFZM) technique in a high vacuum and furthermore by two types of the novel advanced EBFZM techniques. In case of the latter, EBFZM treatments have been done in the atmosphore of low pressure of hydrogen (P_<H2>=10^<-3> to 10^<-5> Pa) and with a superimposed DC electric current (500 to 1000 A/cm^2) on the sample rods, respectively.After the conventional EBFZM treatment, carbon and sulfur contents are found to be reduced by their distribution caused by the zone pass, while the reduction of exygen and nitrogen contents are scarcely observed for neodymium and lanthanum. Metallic impurities having vapor pressures higher than neodymium and lanthanum, such as calcium and magnesium, can be removed through the vaporization. While the reduction of iron, sillicon and copper are not possible through vaporization, but they can be redistributed during zone passes. The residual resistivity ratios of neodymium and lanthanum increased after the EBFZM as a result of the decrease of respective impurities.On the other hand, the advanced EBFZM techniques are expected to be more effective for reduction of non-metallic impurities from Nd and La than the conventional one. However it is recognized that we should, first of all, investigate and find out the good conditions for the stable zone melting on the advanced EBFZM treatment, to utilize the purification effect of it on rare earth metals.