A simple and inexpensive method for rapid synthesis of MgB2 superconductor

doi:10.1016/j.matlet.2006.03.012

Materials Letters

Volume 60, Issue 28, December 2006, Pages 3328-3331

https://doi.org/10.1016/j.matlet.2006.03.012 Get rights and content

Abstract

MgB₂ samples were prepared by a sealed tube method and a systematic study on phase formation at different reaction temperatures was conducted. Phase analysis and structural studies were carried out using XRD and SEM together with optical microscope. Phase pure MgB₂ with better microstructure was obtained at 700 °C in less than 5 min. The synthesis method adopted here considerably reduces the overall production cost and the complexity of manufacturing procedure.

Introduction

The recent discovery of superconductivity in MgB₂[1], a simple binary intermetallic, has triggered great scientific and industrial interest as this material has a transition temperature (T_C) of 39 K which is higher than any of the low-T_C compound and higher than that predicted by BCS theory [2]. The relatively high T_C and the better current carrying capacity [3], [4], [5], [6] make it a promising material to replace low-T_C conductors as well as for cryogen free operations, supported by favourable properties such as lesser anisotropy and material complexities, absence of weak links [7], low cost, light weight, longer coherence length of ∼ 5 nm, weak thermal fluctuations and isotope effect [8], [9].

Mainly MgB₂ based superconductors are fabricated by either in situ (heat treatment of the powder mixture of Mg and B) or ex situ (sintering of commercially available MgB₂ powders) methods. For superconducting applications, high quality MgB₂ powder is required. But it is very difficult to obtain phase pure MgB₂ because Mg is extremely volatile and the difference of melting temperature between Mg and B is around 1500 °C. Mg itself is a very reactive element and it oxidizes during powder production, handling, etc. Birkedal et al. [10] found that MgO content in commercially available MgB₂ amounts more than 5 wt.% on an average. These and other impurities tend to degrade the transport properties of sintered MgB₂ wires [11], [12]. As of today the well accepted method for the production of MgB₂ based products is the in situ synthesis [13], [14], [15], [16], [17], since it provides better grain connectivity and is easier to create artificial pinning centres.

The present work deals with the rapid synthesis of MgB₂ through liquid–solid reaction between Mg and amorphous B by a method designated herein as Powder-in-sealed tube (PIST) method using stainless steel (SUS 304) tubes. So far Fe and its alloys have been reported to be the most suitable sheath material [18], [19], [20] for the preparation of MgB₂ since it is chemically inert with Mg and B and is having better hardness and strength. Thus by considering various alternatives, we selected SUS 304 (Fe with 20% Cr, 10% Ni, 2% Mn, 1% Si and traces of other elements) as the sheath material for MgB₂ preparation. The preparation route illustrated here can significantly reduce the evaporation and oxidation of Mg, cost of synthesis by avoiding expensive Nb/Ta tubes/foils, inert gases and special furnaces.

Section snippets

Experimental details

MgB₂ samples were prepared by in situ powder-in-sealed tube (PIST) method to suppress loss of Mg caused by evaporation and oxidation using stainless steel (SUS 304) tubes. Commercially available pure SUS 304 tubes of 10 cm long with an outside diameter (OD) of 6 mm and inside diameter (ID) of 4 mm were used for synthesis. One end of tube was pressed uniaxially at a pressure of ∼ 1 GPa using a hydraulic press (HERZOG TP 20P) so that it became tape shaped. Stoichiometric weights of commercially

Results and discussion

Fig. 1 shows the photograph of a typical tape specimen prepared by the present experiment. The stainless steel tube used for filling the powder is also shown in the photograph. The heat-treated samples were subjected to XRD analysis by mechanically peeling off the sheaths and grinding the tape shaped core in to powdered form. Fig. 2 shows the XRD patterns of the samples heated at 670 °C, 700 °C, 750 °C and 800 °C for 5 min. The XRD patterns of the samples reveal that almost single phase MgB₂ is

Conclusion

Phase pure MgB₂ has been successfully synthesized by a powder-in- sealed tube method using stainless steel tubes at a temperature as low as 700 °C in few minutes. Preliminary results show that the method is effective to completely suppress loss of Mg vapour and protect the reaction mixture from oxidation when the sealed tube is heated in air. The faster kinetics favoured by the Mg vapour pressure at the heat treatment temperature is responsible for the rapid formation of MgB₂ at relatively low

Acknowledgements

The authors, R.G. Abhilash Kumar, K. Vinod and R.P. Aloysius, acknowledge the Council of Scientific and Industrial Research (CSIR), India for providing research fellowships.

References (20)

R. Flukiger et al.
Physica, C
(2003)
W. Goldacker et al.
Physica, C
(2002)
P. Lezza et al.
Physica, C
(2004)
A. Malagoli et al.
Physica, C
(2002)
J. Nagamatsu et al.
Nature
(2001)
W.L. McMillian
Phys. Rev.
(1968)
S.X. Dou et al.
Appl. Phys. Lett.
(2002)
J. Wang et al.
Appl. Phys. Lett.
(2002)
K. Komori et al.
Appl. Phys. Lett.
(2002)
D.C. Larbalestier et al.
Nature
(2001)

There are more references available in the full text version of this article.

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Citation Excerpt :
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MgB₂ phase formation of samples with stoichiometric ratio of 1:2, prepared by sintering at different nine temperature values (500–900 °C) for 1 h were determined and examined by X-ray Diffractometry (XRD), Scanning Electron Microscopy (SEM) methods. In order to support the results obtained from the above measurements and analyses the Mg:B (1:2) powder was subject to thermal studies. In conjunction with this, the thermal behaviors of the non-sintered powder samples were also studied their characteristics via thermal analysis techniques including Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) simultaneously. During the thermal analyses, Mg:B (1:2) powder was placed in an Al₂O₃ cup with a lid were investigated at different heating rates (5, 7.5, 10, and 15 °C/min) under high-purity Argon atmosphere. By analyzing the graphics gathered from the measurement results the effect of fundamental thermal events on MgB₂ phase formation was deeply discussed by considering some data such as, crystallization, melting point, oxidation and evaporation, which can mainly be obtained from a usual thermal analysis technique. The peak temperatures of exothermic lines in DSC curves that indicate the formation of MgB₂ were determined by derivative lines of the curves. With help of this information, the value of activation energy of MgB₂ phase was found as E_MgB2 = 219.9 kJ/mol by Kissinger Method. Moreover, in order to study the superconductivity of the samples; the sample sintered at 900 °C which was showing a considerable single phase property, was chosen for AC susceptibility measurement. For this sample, the onset temperature which is also called the transition temperature for superconductivity phase was found as T_c = 38.7 K.
Doping effect of nano-SiC on structural and superconducting properties of MgB<inf>2</inf> bulks prepared by PIST method in air
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Bulk MgB₂ samples added with 0, 2, 5, 10 and 15 wt% of SiC nanoparticles were prepared by a powder-in-sealed-tube (PIST) method. XRD analysis shows the presence of secondary phase Mg₂Si and some unreacted SiC as impurities in MgB₂ matrix in SiC added samples. The a axis length decreases with increasing SiC doping level which is mainly due to carbon substitution at boron site which causes local strains in MgB₂ lattice. From SEM analysis, it is found that as the addition level of SiC increases the sharpness of MgB₂ grain boundaries loses and more grains coalesce to form bigger molten-like grains. DC magnetization measurements show systematic variations in T_C and ΔT_C as SiC doping increases. The in-field critical current density [J_C(H)] is highly enhanced for all doped samples and it is more for 10 and 15 wt% SiC added samples at higher fields. The uniformly dispersed nanosize intragrain impurities as seen in TEM and the lattice distortions caused by C substitution are the reasons for enhanced J_C(H) and F_P(H) at higher fields in doped samples.
Enhanced superconducting properties of bulk MgB<inf>2</inf> prepared by in situ Powder-In-Sealed-Tube method
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A systematic study on the superconducting properties of polycrystalline MgB₂ synthesized by in situ Powder-In-Sealed-Tube technique is carried out at different temperatures (750–900 °C). Both XRD and SEM results show well-crystallized MgB₂ grains in all the samples and grain size is found to be increasing with the sintering temperature. Sharp superconducting transitions are observed for all samples, irrespective of sintering temperatures, which implies the high degree phase purity and homogeneity of MgB₂ formed, while J_C(H) plot gives sample dependent critical current density. The samples heat treated at relatively low temperatures show enhanced flux pinning and hence improved J_C(H) performance. The reduced grain size and hence increased density of grain boundary pinning centers of MgB₂ bulks synthesized at low temperature are mainly responsible for the enhanced flux pinning and J_C.
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The effects of starting Mg particle size on the reactivity of Mg with B, and on remnant Mg in in situ MgB₂, and their influence on the superconducting system are studied. Samples were prepared by a powder-in-sealed tube (PIST) method, heat treated at 850 °C for 2 h in air and were characterized using XRD, SEM and magnetization measurements. As the particle size of Mg powder increases, residual Mg increases significantly. The MgB₂ prepared using smaller sized Mg powder does not have any residual Mg and show the best infield critical current density (J_C (H)).
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A simple and inexpensive method for rapid synthesis of MgB2 superconductor

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusion

Acknowledgements

Physica, C

Physica, C

Physica, C

Physica, C

Nature

Phys. Rev.

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

Nature

A simple and inexpensive method for rapid synthesis of MgB₂ superconductor