Trapped Field Properties of Large Disk MgB$_{2}$ Bulks Fabricated by an In-situ Infiltration and Reaction Method Using an Amorphous B Preform Containing Dilute Mg

Abstract

An in-situ infiltration and reaction (IR) method is one of the most promising methods for the mass production of dense MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a filling factor of over 90%. This is because it does not require an apparatus that applies physical pressure during synthesis, in contrast to the hot isostatic pressing, hot pressing, and spark plasma sintering methods. To promote the infiltration of Mg melt into the B preform, a low-reactivity crystalline B has usually been used to create MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks with centimetric dimensions. In this paper, we attempted to fabricate large MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks by the IR method using highly reactive amorphous B, which should result in a high critical current, as reported in the literature. To promote the intrusion of Mg melt, we mixed a small amount of Mg into the amorphous B preform, which is expected to give a similar effect to the socalled premix method. We successfully produced IR-processed MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> disk bulks, of 20 mm diameter and 5 mm thickness, at a reaction temperature of 700°C with a holding time of 9 or 24 h. A trapped field BT of 1.85 T at 20 K was obtained at the surface centers of the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks, which is comparable with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> values of dense MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks prepared by the hot isostatic pressing, hot pressing, and spark plasma sintering methods. Therefore, we can conclude that the Mg premixing method is an effective way of preparing dense MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulks with a high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> by the IR process using amorphous B.