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Chapter IV Thermal Studies of …..
Where, = (W0 – W) /(W0 – Wf), W0 = Initial weight, W = Weight at time t,
Wf = Final weight, n = Order of the reaction, A = Frequency factor, E =
Activation energy of the reaction, R = Gas constant, a = Heating rate in
deg.min -1
To determine the value of activation energy and order of reaction, a plot of
log10[{1 – (1- ) 1 – n }/ {T 2 (1– n) }] versus 1/T is drawn for different values of
n. The best linear fit gives the correct value of n. The value of activation
energy can be calculated from the slope of a linear plot. The value of
frequency factor can be obtained from equation (4.1). Equation (4.1) is
applied for all values of n, except n = 1. For n =1, the modified equation has
been proposed [21].
log( 1 )
2
T
1n
log
log 10
10
AR 2RT
E
.
1
aE E
2.
3RT
173
(4.2)
Figures (4.8 - 4.11) show the best linear fitted plots drawn for Coats and
Redfern relation for pure and different amount of (0.3, 0.4 and 0.5 wt. %) L-
histidine, L-threonine and DL-methionine doped KDP crystals for dehydration
process.
Figure: 4.8 The plot of C-R relation for Pure KDP crystal.