Kissinger method was the first kinetic free method based on differential thermal analysis (DTA) data, applying heat transfer differential partial equation to the heat which is transferred to or from a sample in a DTA cell, allied to Arrhenius equation. It is still applied also to curve data obtained by derivative thermogravimetry (DTG) and/or by differential scanning calorimetry (DSC). By this method the activation energy (Ea) can be obtained from at least three constant heating rate (?) curve data, plotting respective values of In (?.Tm-2) versus Tm-1, where Tm is the temperature of maximum transformation rate, which corresponds to the temperature of the maximum or minimum of the considered DTA, DTG or DSC peak. From the plot angular coefficients equal to -Ea. R-1, the respective Ea value is calculated, where R the Universal Gas Constant. It must be noted that, as Kissinger method assumes a constant Ea value during the entire transformation peak and this rarely occurs, currently it is used to have the mean activation energy of a selected transformation peak, which allow a fast evaluation when many transformation peaks occur. As the activation energy is a function of the conversion degree of a transformation, due to the fact that kinetic mechanisms are function of the conversion degree, except for zero order transformations, other thermal Analysts beginning by Ozawa and Flynn-Wall, developed the so called isoconversional free kinetic methods, based on the fact that, if the sample is the same, at a same conversion degree, the activation energy of a transformation is the same, independently of the heating rate. Thus, all the kinetic free methods which were developed afterwards, were mostly applied to same ? conversion degree thermogravimetric data, because, independently of the complexity of the function of the kinetic model, its value is constant when comparing data of different heating rates at same ?. The main differences consist on the admitted kinetic model and hypothesis used to proceed the integration of the differential Arrhenius equation, expressed in terms of the specific kinetic model function. Thus, depending on each admitted hypothesis, for each considered ? conversion degree, when there is an effective correlation, straight lines of In ?, ln(?.T?-1) or ln(?.T?-2) versus T?-lare obtained, from which the values of E? are obtained, as in Kissinger method. The present developed isoconversional hypothesis and kinetics free method uses directly the Arrhenius equation in its differential equation expression, as a function of the used heating rate and other experimental parameters that can be directly measured from respective TG and DTG curve data, obtained at different heating rates. Without using any integration method or assuming any hypothesis or kinetic model, but only using thermal analysis measured parameter data, the method was applied to the same example of the standard isoconversional ASTM 1641-16 kinetic method, showing very compatible results of activation energies. It was also applied to estimate the activation energies of an oil sample at different conversion degrees, when heated in inert atmosphere, obtaining very similar values to those calculated by three other conventional and well known isoconversional methods, using the above correlations.
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