On the isothermal kinetics analysis of transformations in metastable systems: combined use of isothermal and non-isothermal calorimetry

Abstract

A procedure to optimize the isothermal calorimetric data of very slow transformation processes of metastable systems is proposed. The method uses an experimental baseline to identify the transitory effects due to the equipment. Moreover, the combined use of isothermal and non-isothermal results is shown to be effective in overcoming the intrinsic problems of low signal and signal drift for such processes. The procedure has been applied to the analysis of the nanocrystallization kinetics of the Fe₆₀Co₁₈Nb₆B₁₆ alloy at different devitrification stages. Based on microstructural observations, an instantaneous growth approach was assumed and a phenomenological expression of the dependence of the nucleation frequency with both the transformed fraction and the temperature was obtained.

Acknowledgments

This work was supported by the Spanish Government and EU FEDER (Project MAT 2004-04618) and by the PAI of the Regional Government of Andalucía (Project PO6-FQM-01823) (Spain). J.S.B. acknowledges a research contract from this Regional Government.