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

• Published in: Philosophical magazine (Abingdon, England) Vol. 87; no. 27; pp. 4151 - 4167
• Main Authors: Blázquez, J. S., Millán, M., Conde, C. F., Conde, A.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 21.09.2007; Taylor and Francis
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Materials science; Methods of crystal growth; physics of crystal growth; Nucleation; Physics; Solid-solid transitions; Specific phase transitions; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Quaternary alloys; Frequency dependence; Nucleation; Metastable states; Crystallization; Niobium alloys; Nanostructures; Boron alloys; Phenomenological model; Equipment; Growth mechanism; Isothermal transformations; Calorimetry; Kinetics; Microstructure; Cobalt alloys; Nanocrystal; Iron base alloys
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786430701530990

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 Fe 60 Co 18 Nb 6 B 16 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.