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Chapter IV Thermal Studies of …..
neodymium tartrate. They also calculated various kinetic parameters and
suggested that the decomposition process took place according to cylindrical
kinetic model. The kinetics of dehydration of gypsum [26], lithium sulphate
monohydrate single crystals [27] as well as the kinetic and thermodynamic
parameters of decomposition of chromate in different gas atmosphere [28]
has been evaluated.
Usually, the kinetic parameters can be evaluated from the TG curves
by applying several equations [21-23], which are proposed by different
authors on the basis of different assumptions to the kinetics of the reaction
and the Arrhenius law. These equations are as follows:
(1) Coats and Redfern Relation
(2) Horowitz and Metzger Relation
(3) Freeman and Carroll Relation
However, in the present investigation, the Coats and Redfern
relation is discussed in detail because it facilitates not only to evaluate the
activation energy and order of reaction but also the frequency factor. Thus, it
helps to evaluate the thermodynamic parameters further.
The use of thermogravimetry data to evaluate the kinetic parameters of
solid state reaction involving weight loss has been investigated by many
workers [29-31]. The kinetic parameters of dehydration process of pure and
different amount of (0.3, 0.4 and 0.5 wt. %) amino acids (L-histidine, L-
threonine and DL-methionine) doped KDP crystals were evaluated by using
the Coats and Redfern relation [21], which is as follows,
1
T
1
1n
( 1
n)
log
log10 2
10
AR
2RT
E
.
1
aE
E
2.
3RT
172
(4.1)