## *H function H T H K* - =- ( ) (298.15 ) (15)

is expressed in usual form of *G*#

http://dx.doi.org/10.5772/55145

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the rate of dehydroxylation process decreases.

ence of *G*#-function and *H*#-function.

properties are listed in Table. 7.

function and *H*#

In Fig. 18(b) the temperature dependence of Δ*H*#

**3.7. Properties of artificial termite nest material analogue**


$$
\Delta S^\ddagger = R \left[ \ln \left( \frac{h \ A}{k\_B T} \right) - 1 \right] \tag{12}
$$

$$
\Delta G^\ddagger = \Delta H^\ddagger - T\,\Delta S^\ddagger = -RT\,\ln K^\ddagger\tag{13}
$$

Table 6 shows the overview of average values of thermodynamic results calculated for activated complex according to Eq. 10 – 13 for interval of Δ*T* according to Fig.17.


**Table 6.** Thermodynamics of thermal transformation of kaolin from termite nest.

The negative value of entropy (Δ*S*# < 0) indicating formation of more ordered transition state during dehydroxylation is out of the usual findings for thermal decomposition of kaolinite. Since pure well defined sample of kaolin shows mostly Δ*S*# > 0, SOM interacting with clay phase are responsible for this behaviour.

Theassessedkinetic tripletof combustionofSOMshows thattheactivationenergyoftheprocess is close tothe activationenergyfordehydroxylationbuttheburningof SOMproceeds fasterdue to the higher *A* and the lower *n*. The gas products of burning of SOM (Fig.15(b)) diffuse through the kaolinite aggregates and increase the pressure of water vapour affecting the thermodynam‐ ics of dehydroxylation via the equilibrium constant (Eq.13; the Δ*G*# increases due to negative value of Δ*S*# ) <sup>20</sup>. The temperature dependence of Δ*G*# determined by extrapolation of the values calculated from the experiment is shown in Fig.18 for both processes. From the kinetic point of view which is given by Eq.10, the rate constant of dehydroxylation with temperature increases more slowly than for the combustion process of SOM. In the other words, increasing pressure

<sup>20</sup> It must be pointed that combustion of SOM is strongly affected by the content of individual kind of humic substances and the both processes (combustion of SOM and dehydroxylation) show mutual relationship. For example, intensive origin of water vapor slows down diffusion of oxygen, leads to reducing conditions, changing composition of product and slowing down the rate of process [74].

of water vapour slows down the rate of decomposition of activated complex into product and the rate of dehydroxylation process decreases.

The thermodynamic parameters of activated complex, including free energy (Δ*G*#
