Authors:J. Criado, M. Gonzalez, A. Ortega, and C. Real
It has been demonstrated that the kinetic data on solid-state reactions show a good fitting to the expressiong(α)=kt, regardless of the nature of theg(α) function previously assumed for performance of the calculations. Moreover, the activation energy value obtained from the
Arrhenius law is quite independent of the kinetic function assumed.
Authors:E. Donoso, A. Zúñiga, M. Diánez, and J. Criado
The precipitation processes in a Cu–1.0 at.%Co–0.5 at.%Ti (Cu–1.5 at.%Co2Ti) alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardeness
measurements. The analysis of the calorimetric curves from room temperature to 900 K shows the presence of two exothermic
reactions attributed to the formation of CoTi and Co2Ti particles in the copper matrix. On the basis of enthalpy calculations, it was found that the decomposition begins with
the precipitation of CoTi, followed by the formation of Co2Ti particles. The activation energies calculated using the modified Kissinger method were lower than the ones corresponding
to diffusion of cobalt and titanium in copper. Kinetic parameters were obtained by a convolution method based on the Johnson–Mehl–Avrami
(JMA) formalism. The values obtained for the parameter n were indicative of a particle nucleation process from preexistent
nuclei. Microhardness measurements and TEM micrographs confirmed the formation of the mentioned phases.
Authors:J. Criado, L. Pérez-Maqueda, M. Diánez, and P. Sánchez-Jiménez
The SCTA method implies to control the temperature in such a way that
the reaction rate changes with the time according to a function previously
defined by the user. Constant Rate Thermal Analysis (CRTA) is one of the most
commonly used SCTA methods and implies achieving a temperature profile at
which the reaction rate remains constant all over the process at a value previously
selected by the user. This method permits to minimize the influence of heat
and mass transfer phenomena on the forward reaction. The scope of this work
is to develop a universal CRTA temperature controller that could be adapted
to any thermoanalytical device. The thermoanalytical signal is programmed
to follow a preset linear trend by means of a conventional controller that
at the time controls a second conventional temperature programmer that forces
the temperature to change for achieving the trend programmed for the thermoanalytical
signal. Examples of the performance of this control system with a Thermobalance
and a Thermomechanical Analyser (TMA) are given.
Authors:J. M. Criado, L. A. Pérez-Maqueda, and P. E. Sánchez-Jiménez
The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation
energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has
been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence
of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach
used for carrying out the kinetic analysis of TG data.