An extended Kissinger equation for near equilibrium solid–gas heterogeneous transformations

• An extension of the Kissinger for reversible solid–gas trasformations is proposed.
• The equation applies to solid–gas heterogeneous transformations near equilibrium.
• The driving force due to the partial pressure of decomposition gas is included.
• The presence of partial pressure leads to overestimations of activation energy.

In this paper a generalization of the Kissinger equation for solid–gas heterogeneous transformations in the presence of a non-zero partial pressure is proposed, taking into account both thermodynamics and kinetics. A mathematical derivation of the extended equation obtained by incorporating a thermodynamic driving force factor into the rate equation is reported. The proposed method is applicable to the non-isothermal (isochronous) determination of the decomposition apparent activation energy of solids leading to the reversible evolution of gas in near equilibrium conditions. The proposed equation could be particularly useful when the experimental conditions used for the kinetic investigations do not allow to keep the system far from equilibrium during the whole experiment, e.g. in the case a volumetric device is employed to track the extent of reaction.