In:
Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 70, No. 19 ( 2021), p. 197401-
Abstract:
Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 was previously studied as a promising hydrogen storage material, because of its high gravimetric storage capacities for hydrogen and suitable thermodynamic properties. Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 began to decompose at about 300 ℃, and formed MgB〈sub〉2〈/sub〉 at the end of hydrogen desorption process with the weight content of 14.9% of hydrogen lost. Aside from the prominent hydrogen storage property, the decomposition process from Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 to MgB〈sub〉2〈/sub〉 can be a potential method for fabricating superconducting MgB〈sub〉2〈/sub〉 at a low sintering temperature. In this paper, MgB〈sub〉2〈/sub〉 bulk was prepared by an 〈i〉in-situ〈/i〉 reaction, using the Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 pressed block as a precursor. The resistance change of the sample was monitored during the Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 decomposition process and the resistance-temperature (〈i〉R〈/i〉-〈i〉T〈/i〉) curve of this process was recorded. Phase of MgH〈sub〉2〈/sub〉, Mg and B were formed as the block slowly release its hydrogen before MgB〈sub〉2〈/sub〉 occurred. According to the 〈i〉R〈/i〉-〈i〉T〈/i〉 curve, the phase formation of MgB〈sub〉2〈/sub〉 started in a relatively low temperature of 410 ℃. Because MgB〈sub〉2〈/sub〉 was critically formed by Mg and B derived from Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉, we can compare our formation temperature with previous study on MgB〈sub〉2〈/sub〉 prepared by Mg and B in different particle size. The fitting result indicated that the particle size of Mg and B harvest from Mg(BH〈sub〉4〈/sub〉)〈sub〉2〈/sub〉 decomposition was only 3.4 nm on average. The nearly atomic level mixture of Mg and B resulted in a high chemical reactivity, which was the main reason for low sintering temperature. X-ray diffraction results showed that the purity of MgB〈sub〉2〈/sub〉 was 95.2%, and the size of MgB〈sub〉2〈/sub〉 grains was 10–18 nm. SEM images showed that the MgB〈sub〉2〈/sub〉 bulk had a porous structure and poor connectivity, which was caused by large amount the hydrogen release during the decomposition. MgB〈sub〉2〈/sub〉 nanofibers can also be observed inside the bulk. In the superconductivity test, the superconducting transition temperature of the bulk was 35 K. After all, such 〈i〉in situ〈/i〉 method to fabricate MgB〈sub〉2〈/sub〉 showed a great advantage in some aspects, as its low-cost precursors, low sintering temperature, small grain-size and high superconducting transition temperature in the formed MgB〈sub〉2〈/sub〉, which have the potential in industrial scale fabrication of MgB〈sub〉2〈/sub〉 bulks and wires.
Type of Medium:
Online Resource
ISSN:
1000-3290
,
1000-3290
DOI:
10.7498/aps.70.20210620
Language:
Unknown
Publisher:
Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
Publication Date:
2021
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