Chemical Processes - Isoconversional Kinetics of Thermally Stimulated Processes - page 215

4.4.2 Isoconversional Treatment

According to Eq. 4.64, the mass of a solid product B s is less than the mass of a solid
reactant A s by the mass of released gas C g . The decrease in mass that accompanies
thermal decomposition of solids is usually large enough to be accurately measured
by TGA. The use of this technique is the most common way of measuring the kinet-
ics of thermal decomposition.
Calcium carbonate appears to be the compound whose thermal decomposition
has been studied most frequently. In 1987, Maciejewski and Reller [ 108 ] published
a statistical distribution of 168 values of the activation energy reported for this pro-
cess (Fig. 4.41 ). The values range from 100 to over 300 kJ mol − 1 , with absolute
majority of the values falling in a somewhat narrower range: 170 and 250 kJ mol − 1 .
The wide spread of the values was proposed [ 108 ] to be due to the effect of experi-
mental conditions on the reversible decomposition. Although this effect is undeni-
able (see, for example, Fig. 4.36 ), the method by which the kinetic triplets were
estimated is just as important. The authors did not comment what fraction of the
values was estimated by using single-heating-rate methods that are presently known
[ 109 - 113 ] to be computationally flawed and, thus, generally incapable of producing
reliable kinetic triplets.
Considering that the single-heating-rate methods had been dominating the field
until the beginning of the twenty-first century, one can safely infer that a great many
numbers presented in Fig. 4.41 are no more than computational mishaps. This in-

Fig. 4.41 Statistical distribu-
tion of the literature values
for the activation energy of
the thermal decomposition
of calcium carbonate. Each
dot represents an individual
literature value. (Reproduced
from Maciejewski and Reller
[ 108 ] with permission of
Elsevier)