Reducing the effects of noise in the calculation of activation energy by the Friedman method

• A modified version of the Friedman method is proposed in order to decrease the effect of noise.
• The method is applied to simulated data and more accurate activation energy values than those given by the Friedman method are obtained.
• The proposed method is used to determine activation energy on the thermal degradation of γ-Ti(PO4)(NH4HPO4).

The Friedman method for analysis of kinetic parameters of solid-state reactions has been widely used. One of the drawbacks of this method is its sensitivity to noise which can be caused by both experimental error and the intrinsic inaccuracy of the differential methods, particularly for non-isothermal kinetic data obtained by means of thermogravimetric analysis (TGA). This paper proposes a modified version of the Friedman method in order to decrease the effect of noise and consequently obtain more accurate activation energy values. The new method is based on the idea of considering, for a given value of the extent of conversion α, not only information corresponding to α but also data in its neighbourhood. To check the procedure, it is applied to simulated data and the activation energy obtained is compared with the preset value and that given by the Friedman method. Moreover, the proposed method is used to determine the activation energy on the thermal degradation of γ-Ti(PO4)(NH4HPO4) compound as a function of the extent of conversion.