Chemistry Reference
In-Depth Information
Chapter 2
Isoconversional Methodology
2.1
Evolution of Isoconversional Methods
You must have accurate and honest weights and measures.
Deuteronomy 25:15
2.1.1
Early Methods
The birth of isoconversional methods dates back to the 1925 work by Kujirai and
Akahira [
1
]. In their work, they applied thermogravimetric analysis (TGA) data to
follow the decomposition kinetics of some insulating materials under isothermal
conditions. The mass loss data were fitted to an empirical equation
Q
T
(2.1)
log
t
=−
Fw
(
),
where
w
is the mass loss in percentage of the initial value,
t
is the time to reach the
extent of decomposition
w
at different temperatures, and
Q
is what they called “ma-
terial constant” that determines the temperature dependence of the decomposition
rate. The
Q
values were estimated as a slope of log
t
versus
T
−1
straight line.
It is not difficult to translate the meaning of
Q
and
F
(
w
) to modern kinetic lan-
guage. Our basic kinetic equation can be written as:
d
d
α
−
E
RT
=
A
exp
f
(
α
).
(2.2)
t
Its integration for isothermal conditions yields:
(2.3)
d
α
α
−
E
RT
α
∫
g
()
α
≡
=
A
exp
t
,
f
()
0
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