Effect of additions of Ca compounds to the filling powder on the reduction of MgO and the critical current density properties of ex situ processed MgB2 tapes
Effect of additions of Ca compounds to the filling powder on the reduction of MgO and the critical current density properties of ex situ processed MgB2 tapes
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DOI：
10.1016/j.jallcom.2016.01.027
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发表时间：
2016-04
影响因子：
6.2
通讯作者：
H. Fujii;Akira Ishitoya;S. Itoh;K. Ozawa;H. Kitaguchi
中科院分区：
文献类型：
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作者：
H. Fujii;Akira Ishitoya;S. Itoh;K. Ozawa;H. Kitaguchi
本文研究了在填充粉中添加Ca化合物CaC2和CaH2对原位法MgB2带材输运临界电流密度（Jc）特性的影响。这些添加剂有望减少收到的商业MgB2粉末中的MgO，并改善带材中MgB2的晶粒耦合。与热处理后的MgB2粉末相比，MgB2粉末和Ca化合物混合粉末的热处理既导致MgB4的消失，又导致CaB6和Mg的形成。对于添加CaH2的混合物，它们观察得更清楚。MgO的含量降低，这些化合物的添加。MgB 2的a轴和c轴参数均未因添加而改变，表明MgB 2中没有发生Ca取代Mg和C取代B的反应。添加CaC2的手拌填充粉试样的Jc性能下降，而添加CaH2的手拌填充粉试样的Jc性能略有提高。当使用球磨混合物时，a轴参数的轻微收缩仅由CaC2添加发生。虽然添加引起的反应类似于那些观察到的手混合粉末，MgO含量减少更明显，相比MgB2含量。CaC2和CaH2的添加分别增强了带材在高场和低场区域的Jc性能。这些增强归因于碳替代、改善的晶粒耦合和MgB2含量的增加。
We have studied the effect of additions of Ca compounds, CaC2and CaH2, to the filling powder on the transport critical current density (Jc) properties ofex situprocessed MgB2tapes. These additives are expected to reduce MgO present in as-received commercial MgB2powder and improve the grain coupling of MgB2in the tapes. Heat treatment of the hand mixed powders, MgB2and the Ca compounds, brings about both disappearance of MgB4and formation of CaB6and Mg, compared with heat treated MgB2powder. They are observed much more clearly for the mixtures with CaH2addition. The MgO content decreases by the additions of those compounds. Neither of thea-axis and thec-axis parameters of MgB2are changed by the additions, suggesting no reactions of substitutions of Ca for Mg and C for B in MgB2. TheJcproperties of the tape samples using the hand mixed filling powder with CaC2addition degrade, whereas those with CaH2addition are slightly improved. When using the ball milled mixtures, slight contraction of thea-axis parameter occurs only by CaC2addition. Although the additions cause the reactions similar to those observed for the hand mixed powders, the MgO content reduces more clearly, compared with the MgB2content. TheJcproperties of the tapes are enhanced in the high-field and low-field regions by the additions of CaC2and CaH2, respectively. These enhancements are attributed to the carbon substitution, the improved grain coupling and the increased content of MgB2.