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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: [email protected]
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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

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