Evaluation of aging precipitation kinetics and potential in aluminum alloys using indiscriminately integrated peak areas
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reported by Neijmeijer and Koster,[9] (Figure 8). Even though both of the processes are diffusion controlled, the variation in the activation energy is due to the difference in nature of the reactants (precursors). In the present work, Nb3Sn was formed using elemental niobium and tin powder as the starting material, while Neijmeijer and Koster made Nb3Sn via the reaction between Nb6Sn5 powder and elemental niobium.[10] The powder mixture comprised of stoichiometric proportions of elemental niobium and tin powder was mechanically alloyed for 3 hours and the mechanically alloyed powder mixture was heat treated. X-ray diffraction studies failed to show the presence Nb3Sn formation in powders milled for up to 3 hours. This observation is consistent with the findings reported by Cho et al.[6] While MA resulted in Nb-Sn solid solution, the reaction leading to the formation of Nb3Sn occurred during the subsequent heat treatment of the powder mixture. The important conclusion that can be drawn from the current studies is that the Nb-Sn powder mixture mechanically alloyed for a short duration could be used as an effective precursor for making the Nb3Sn superconductor. From the results obtained, it is clear that MA would ensure complete and near instantaneous transformation of the Nb-Sn powder mixture to Nb3Sn thereby, eliminating the need for independent long duration heat treatments that are normally required during the processing of Nb3Sn superconductors. The activation energy associated with the transformation of the mechanically alloyed Nb-Sn powder mixture to Nb3Sn is 312 kJ mole1. This value is marginally higher than the one reported for Nb3Sn formation via reaction between Nb6Sn5 powder and elemental niobium. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.
http://128.104.186.21/asc/pdf_papers/theses/cmf02msc.pdf http://superconductors.org/Type2.htm http://www.americanmagnetics.com/tutorial/supercon.html http://hyperphysics.phy-astr.gsu.edu/hbase/solids/scond.html#c5 http://www-dapnia.cea.fr/Stcm/nb3sn/pdf/lecture3.pdf Y.S. Cho and C.C. Koch: Mater. Sci. Eng., 1991, vol. A141, pp. 139-48. H.E. Kissinger: Anal. Chem., 1957, vol. 29, p. 1702. J.H. Flynn and L.A. Wall, J. Res. Nat. Bur. Stand. A Phys. Chem., 1966, vol. 70A, p. 487. 9. J.H. Flynn and L.A. Wall: Polymer Lett., 1966, vol. 4, p. 323. 10. W.L. Neijmeijer and B.H. Kolster: J. Less Common Met., 1990, vol. 160, pp. 161-70.
Evaluation of Aging Precipitation Kinetics and Potential in Aluminum Alloys Using Indiscriminately Integrated Peak Areas in Calorimetry Curves W. SHA This article explores the possibility of evaluating aging precipitation kinetics and potential using differential scanning calorimetry curves without the need of peak separation or
W. SHA, University Reader, is with the Metals Research Group, School of Civil Engineering, The Queen’s University of Belfast, Belfast BT7 1NN, United Kingdom. Contact e-mail: [email protected] Manuscript submitted January 16, 2004. 3012—VOLUME 35A, SEPTEMBER 2004
considering individual precipitation
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