Accuracy in the experimental calorimetric study of the crystallization kinetics and predictive transformation diagrams:
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Accuracy in the experimental calorimetric study of the crystallization kinetics and predictive transformation diagrams: Application to a Ga–Te amorphous alloy N. Clavaguera Grup de F´ısica de l’Estat S`olid, Departament d’Estructura i Constituents de la Mat`eria, Facultat de F´ısica, Universitat de Barcelona, Diagonal 647, 08028-Barcelona, Spain
M. T. Clavaguera-Mora and M. Fontanaa) Grup de F´ısica de Materials I, Departament de F´ısica, Edifici C, Universitat Aut`onoma de Barcelona, 08193-Bellaterra, Spain (Received 25 March 1996; accepted 12 May 1997)
The uncertainties inherent to experimental differential scanning calorimetric data are evaluated. A new procedure is developed to perform the kinetic analysis of continuous heating calorimetric data when the heat capacity of the sample changes during the crystallization. The accuracy of isothermal calorimetric data is analyzed in terms of the peak-to-peak noise of the calorimetric signal and base line drift typical of differential scanning calorimetry equipment. Their influence in the evaluation of the kinetic parameter is discussed. An empirical construction of the time-temperature and temperature-heating rate transformation diagrams, grounded on the kinetic parameters, is presented. The method is applied to the kinetic study of the primary crystallization of Te in an amorphous alloy of nominal composition Ga20 Te80 , obtained by rapid solidification.
I. INTRODUCTION
Kinetics of phase transformation studies include several experimental techniques; in particular, optical or electron microscopy, x-ray or neutron diffraction, electrical resistivity, magnetic susceptibility, M¨ossbauer spectroscopy, thermal analysis, and dilatometry are currently used. One of the thermal analysis methods, specifically differential scanning calorimetry (DSC), is of particular interest in first order phase transformations. It provides the rate of transformation as a function of time or temperature by measuring the heat released or absorbed during the phase change. Isothermal and continuous heating (or cooling) measurements are readily made, although care must be taken to account for heat capacity changes of the sample during the transformation and the peak-to-peak noise and base line drift in the calorimetric signal. The use of DSC data to evaluate kinetic parameters of solid state reaction is well established (see, for instance, Borchardt and Daniels,1 Freeman and Carroll,2 Coats & Redfern,3 and Hugo et al.4 ). The goal of kinetic studies is to determine the kinetic parameters which allow extrapolation of the transformaÙ to broader temperature ranges than those tion rate, x, accessible by DSC measurement. An important tool in this respect is the use of time-temperature-transformation
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Permanent address: Departamento de F´ısica, Facultad de Ingenieria, Universidad de Buenos Aires, Paseo Col`on 850 (1063), Buenos Aires, Argentina.
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J. Mater. Res., Vol. 13, No. 3, Mar 1998
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