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arXiv · 1209.4689

Strongly connected ex-situ MgB2 polycrystalline bulks fabricated by solid-state self-sintering

Hiroya Tanaka·Akiyasu Yamamoto·Jun-ichi Shimoyama·Hiraku Ogino·Kohji Kishio
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Abstract

We have investigated the microstructure, normal-state electrical connectivity, and critical current density of ex-situ MgB2 polycrystalline bulks prepared by systematically varying the sintering conditions under low pressure. Samples heated at a high temperature of ~900°C for a long period showed an increased packing factor, a larger intergrain contact area, and a significantly enhanced electrical connectivity, all of which indicate solid-state self-sintering of MgB2. Sintered ex-situ MgB2 bulks from a laboratory-made ball-milled powder exhibited a greatly enhanced connectivity of 28%, which is the highest connectivity of pressureless ex-situ MgB2 bulks, wires, and tapes. Surprisingly, grain growth did not occur during long-duration (~100 h) sintering in the sintered ex-situ MgB2 bulks. This is in marked contrast to in-situ processed MgB2 samples for which significant grain growth occurred during heat treatment at ~900°C, producing grains that are several tens of times larger than the initial boron grains. Consequently, the critical current density as a function of the external magnetic field at 20 K progressively improved with sintering due to the relatively small grain size and good intergrain connectivity. We thus conclude that solid-state self-sintering is an effective approach for producing strongly connected, dense ex-situ MgB2 polycrystals without grain growth.

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Hiroya Tanaka, Akiyasu Yamamoto, Jun-ichi Shimoyama, Hiraku Ogino, Kohji Kishio. 2012-09-21. Strongly connected ex-situ MgB2 polycrystalline bulks fabricated by solid-state self-sintering. https://doi.org/10.1088/0953-2048%2F25%2F11%2F115022

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