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

摘要

A procedure to optimize the isothermal calorimetric data of very slow transformationprocesses of metastable systems is proposed. The method uses an experimental baselineto identify the transitory effects due to the equipment. Moreover, the combined use ofisothermal and non-isothermal results is shown to be effective to overcome the intrinsicproblems of low signal and signal drift for such processes. The procedure has beenapplied to the analysis of the nanocrystallization kinetics of the Fe60Co18Nb6B16 alloy atdifferent devitrification stages. Based on microstructural observations, an instantaneousgrowth approach was assumed and a phenomenological expression of the dependence ofthe nucleation frequency with both the transformed fraction and the temperature wasobtained