Self-sintering-assisted high intergranular connectivity in ball-milled ex situ MgB2 bulks
Self-sintering-assisted high intergranular connectivity in ball-milled ex situ MgB2 bulks
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DOI：
10.1088/0953-2048/27/11/114001
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发表时间：
2014-10
影响因子：
3.6
通讯作者：
S. Mizutani;A. Yamamoto;J. Shimoyama;H. Ogino;K. Kishio
中科院分区：
文献类型：
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作者：
S. Mizutani;A. Yamamoto;J. Shimoyama;H. Ogino;K. Kishio
为了了解使用无压自烧结技术制备的多晶非原位 MgB2 获得更高晶间连通性的机制，研究了 MgB2 粉末初始粒径的影响。使用球磨粉末在 900 °C 下烧结 24 小时的 MgB2 块体呈现出网络结构，在质量和数量上都改善了晶间耦合。使用正常状态传输测量计算的连通性达到了约 40% 的高值，这与通过 Mg 扩散或高压辅助工艺制造的 MgB2 块体的连通性相当。此外，实现 25-30% 相当高的连通性所需的烧结时间不到 1 小时。值得注意的是，微观结构分析证实了在烧结早期阶段晶间颈和晶界的形成。这些结果表明球磨 MgB2 块体的自烧结比使用 MgB2 粉末未经球磨的烧结进行得快得多。生坯中晶粒间接触点的增加和晶粒之间间隙长度的减少被认为是受激自烧结和电连接性相应增加的根源。
To understand the mechanisms leading to higher intergranular connectivity in polycrystalline ex situ MgB2 prepared using a pressure-less self-sintering technique, the influence of the initial particle size of the MgB2 powder was investigated. MgB2 bulks sintered at 900 °C for 24 h using ball-milled powders exhibited a network structure with both qualitatively and quantitatively improved intergranular couplings. The connectivity calculated using normal-state transport measurements reached a high value of ∼40%, which is comparable to that of MgB2 bulks fabricated via Mg diffusion or high-pressure-assisted processes. Moreover, the sintering time required to achieve a reasonably high connectivity of 25–30% was less than 1 h. Notably, microstructural analyses confirmed the formation of intergranular necks and grain boundaries during the early stage of sintering. These results suggested self-sintering of the ball-milled MgB2 bulks proceeded much more rapidly than those sintered using an MgB2 powder without ball-milling. Increased intergranular contact points and decreased gap length between grains in green compact are assumed to be the origins for the stimulated self-sintering and corresponding increase in the electrical connectivity.