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This paper is a rebuttal to the paper of Zsakó and Somasekharan. It has been shown that the criticisms of Zsakó and Somasekharan are baseless. The procedure proposed earlier by Agrawal to distinguish between true and false compensation effect is reasonable and gives good results. To establish true c.e., it has been reaffirmed that bothTiso and Inkiso are prerequisite.
Some preliminary considerations suggest that the so-called ‘compensation law’ is a result of the misinterpretation of evaluation
procedure. The both parameters: pre-exponential factor and activation energy are calculated from the same set of experimental
data. A confidence ellipse could describe the precision of these parameters. In the case of using the least square method
for straight-line parameters evaluation, we could calculate a axes of the ellipse, using experimental data. If the observed relationship between pre-exponential factor and activation
energy agree with the ‘pre-calculated’ direction of main axis of confidence ellipse, we have a strong support to believe that
the observed ‘compensation’ effect is only an artificial effect of misinterpretation. Some calculations performed for a published
experimental data have confirmed these suspicions. This also, indirectly indicates that precision of such experiments is probably
lower than expected.
On the basis of theoretical TG curves it has been shown that the kinetic compensation effect observed in thermal decomposition reactions is not due to the special form of the Arrhenius equation. Formally, the validity of a linear kinetic compensation law implies the existence of a characteristic temperature at which the rate constants of all reactions have the same value, but this temperature can be higher or lower than the temperatures at which the decomposition takes place.
It is generally accepted that the compensation effect arises when a linear relation between InA andE is detected for a simple reaction taking place over different catalysts or for different reactions over one catalyst. For
a perfect linear relation between InA andE representation of the reaction rate constant in an Arrhenius plot results in a series of straight lines which intersect in
a single point. The importance is stressed of defining unambiguously what is meant by the compensation effect, and it is shown
how the scatter in the values of InA is translated into Arrhenius plots.
Two kinds of compensation mechanism are suggested: a genuine one due to thermodynamic factors and a pseudo one arising from
experimental or data-processing artifacts. It is computationally demonstrated that the choice of reaction mechanism strongly
influences the kinetic parameters determined in thermal analytical studies. It is further shown that the kinetic parameters
determined at different heating rates by using a pseudo reaction mechanism exhibit kinetic compensation that gives the temperature
of the experiment as the so-called isokinetic temperature. A rule of thumb relating to the magnitude of the isokinetic temperature
is suggested to differentiate genuine compensation from pseudo compensation.
A number of 1145 sets of kinetic parameters derived in our earlier papers from TG curves have been worked up. The apparent activation energy and pre-exponential factor values have been found to obey a linear compensation law (isokinetic relation) if the thermal decomposition begins in the same temperature interval, irrespective of the nature of the chemical reaction. The isokinetic temperatureTi has been found to be very close to the mean value of the temperaturesT0.1 at which the conversion becomes equal to 0.1 and atTi the rate constant has been found to be approximately equal to 10−3s−1 in allT0.1 intervals investigated. It is concluded that the kinetic compensation effect observed in heterogeneous non isothermal TG kinetics is not a true one.