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In situ formation process and mechanism of bulk MgB2 before Mg melting

Published online by Cambridge University Press:  31 January 2011

Qing-Zhi Shi ,
Yong-Chang Liu ,
Zhi-Ming Gao ,
Qian Zhao  and
Zong-Qing Ma
Qing-Zhi Shi
Affiliation:
Engineering Research Center of Shape Memory Materials of Ministry of Education, College of Materials Science & Engineering, Tianjin University, Tianjin 300072, People’s Republic of China
Yong-Chang Liu*
Affiliation:
Engineering Research Center of Shape Memory Materials of Ministry of Education, College of Materials Science & Engineering, Tianjin University, Tianjin 300072, People’s Republic of China
Zhi-Ming Gao
Affiliation:
Engineering Research Center of Shape Memory Materials of Ministry of Education, College of Materials Science & Engineering, Tianjin University, Tianjin 300072, People’s Republic of China
Qian Zhao
Affiliation:
Engineering Research Center of Shape Memory Materials of Ministry of Education, College of Materials Science & Engineering, Tianjin University, Tianjin 300072, People’s Republic of China
Zong-Qing Ma
Affiliation:
Engineering Research Center of Shape Memory Materials of Ministry of Education, College of Materials Science & Engineering, Tianjin University, Tianjin 300072, People’s Republic of China
*
a)Address all correspondence to this author. e-mail: licmtju@163.com
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Abstract

Differential thermal analysis, as the main means of measurement, was used to prepare bulk MgB2 samples and monitor the sintering reaction process. Combined with microstructure observation by scanning electron microscopy and x-ray diffraction analysis, the formation process of MgB2 phase at the temperature before Mg melting was summarized. Additionally, a new kinetic analysis (a variant on the Flynn–Wall–Ozawa) method under nonisothermal conditions was used to determine that the reaction between Mg and B powders involves random nucleation followed by an instantaneous growth of nuclei (Avrami–Erofeev equation, n = 2), which can properly explain the in situ formation process of bulk MgB2 at the temperature before Mg melting. The value of activation energy E and the function of conversion f(α) are obtained independently, and thereby the determination of mechanism function is not affected by the value of E. The values of E decrease from 175.418 to 160.395 kJ mol−1 with the increase of the conversion degrees (α) from 0.1 to 0.8. However, as the conversion degrees approach 0.9, the value of E increases to 222.647 kJ mol−1, and the corresponding pre-exponential factor A is about three orders of magnitude larger than the previous ones.

Keywords

Differential thermal analysis (DTA)KineticsPowder
Type
Articles
Information
Journal of Materials Research , Volume 23 , Issue 7 , July 2008 , pp. 1840 - 1848
Copyright
Copyright © Materials Research Society 2008

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References

REFERENCES

1Nagamatsu, J., Nakagawa, N., Muranaka, T., Zenitani, Y.Akimitsu, J.: Superconductivity at 39K in magnesium diboride. Nature 410, 63 2001CrossRefGoogle Scholar
2Dhallé, M., Toulemonde, P., Beneduce, C., Musolin, N., Decroux, M.Flükiger, R.: Transport and inductive critical current densities in superconducting MgB2. Physica C 363, 155 2001CrossRefGoogle Scholar
3Yu, R.C., Li, S.C., Wang, Y.Q., Kong, X., Zhu, J.L., Li, F.Y., Liu, Z.X., Duan, X.F., Zhang, Z.Jin, C.Q.: EELS studies of MgB2 superconductor obtained under high pressure. Physica C 363, 184 2001CrossRefGoogle Scholar
4Podder, A., Bandyopadhyay, B., Mandal, P., Bhattacharya, D., Choudhury, P., Shina, U.Ghosh, B.: Studies of transport properties of MgB2 superconductor. Physica C 390, 191 2003CrossRefGoogle Scholar
5Kumakura, H., Kitaguchi, H., Matsumoto, A.Hatakeyama, H.: Upper critical fields of powder-in-tube-processed MgB2/Fe tape conductors. Appl. Phys. Lett. 84, 3669 2004CrossRefGoogle Scholar
6Cooley, L.D., Kang, K., Klie, R.F., Li, Q., Moodenbaugh, A.M.Sabatini, R.L.: Formation of MgB2 at low temperatures by reaction of Mg with B6Si. Supercond. Sci. Technol. 17, 942 2004CrossRefGoogle Scholar
7Yamamoto, A., Shimoyama, J.I., Ueda, S., Katsura, Y., Horii, S.Kishio, K.: Improved critical current properties observed in MgB2 bulks synthesized by low-temperature solid-state reaction. Supercond. Sci. Technol. 18, 116 2005CrossRefGoogle Scholar
8Liu, Y.C., Sommer, F.Mittemeijer, E.J.: Abnormal austenite– ferrite transformation behaviour in substitutional Fe-based alloys. Acta Mater. 51, 507 2003CrossRefGoogle Scholar
9Yan, G., Feng, Y., Fu, B.Q., Liu, C.F., Zhang, P.X., Wu, X.Z., Zhou, L., Zhao, Y.Pradhan, A.K.: Effect of synthesis temperature on density and microstructure of MgB2 superconductor at ambient pressure. J. Mater. Sci. 39, 4893 2004CrossRefGoogle Scholar
10Feng, Q-R., Chen, C., Xu, J., Kong, L-W., Chen, X., Wang, Y-Z., Zhang, Y.Gao, Z-X.: Study on the formation of MgB2 phase. Physica C 411, 41 2003CrossRefGoogle Scholar
11Brook, R.J.: Pore–grain boundary interactions and grain growth. J. Am. Ceram. Soc. 52, 56 1969CrossRefGoogle Scholar
12Flynn, J.H.: Thermal analysis kinetics—Past, present and future. Thermochim. Acta 203, 519 1992CrossRefGoogle Scholar
13Prasad, T.P., Kanungo, S.B.Ray, H.S.: Non-isothermal kinetics: Some merits and limitations. Thermochim. Acta 203, 503 1992CrossRefGoogle Scholar
14Vyazovkin, S.: Alternative description of process kinetics. Thermochim. Acta 211, 181 1992CrossRefGoogle Scholar
15Ozawa, T.: A new method of analyzing thermogravimetric data. Bull. Soc. Chem. Jpn. 38, 1881 1965CrossRefGoogle Scholar
16Popescu, C.: Integral method to analyze the kinetics of heterogeneous reactions under non-isothermal conditions—A variant on the Ozawa-Flynn-Wall method. Thermochim. Acta 285, 309 1996CrossRefGoogle Scholar
17Liu, Y.C., Shi, Q.Z., Zhao, Q.Ma, Z.Q.: Kinetics analysis for the sintering of bulk MgB2 superconductor. J. Mater. Sci. 18, 855 2007Google Scholar