3.2 Dependence on the intrinsic and morphological changes of the material G(α)

At constant temperature and pressure, the reaction rate depends on intrinsic factors and morphological changes of the solid (defects, crystalline structure, size and morphology of the particles, etc.), i.e., G(α) [34, 35]. Thus, Eq. (5) can be expressed:

$$\frac{da}{dt} = k \times G(a) \tag{6}$$

$$k = K(T) \times F(P),\tag{7}$$

k is the kinetic constant and it contains the temperature and pressure dependences as seen in Eq. (7). Reordering Eq. (6), it is possible to obtain an expression for the evaluation of G(α):

$$\text{g}(a) = \int\_0^a \frac{da}{G(a)} = k \times t,\tag{8}$$

where g(α) is the integral form of the gas-solid kinetic models for the material's changes. The gas-solid kinetic models describe different physical phenomena. There are four main sets of models: (1) nucleation and growth models, (2) geometrical
