Isoconversional Methodology - Isoconversional Kinetics of Thermally Stimulated Processes - page 31

Fig. 2.4 The activation ener-
gies reported by Ozawa [ 14 ]
for the thermal decomposi-
tion of calcium oxalate ( open
circles ) and Nylon 6 ( solid
circles )

α

clues about the reaction mechanisms as well as estimates of the activation energies
of the individual steps [ 29 ].
As mentioned earlier, Eq. 2.11 is based on a very crude approximation of the
temperature integral and, thus, should not be used without performing an iterative
correction as described elsewhere [ 30 , 31 ]. Alternatively, one can use isoconver-
sional methods based on a more accurate approximation to the temperature integral.
Starink [ 32 ] has demonstrated that many of these approximations give rise to linear
equations of the general form:

β E

RT

i α

α

ln = Const − C ,

(2.12)

B

T

, i

α , i

where B and C are the parameters determined by the type of the temperature in-
tegral approximation. For example, Doyle's approximation gives rise to B = 0 and
C = 1.052 that turns Eq. 2.12 into Eq. 2.11 used by the methods of Ozawa and Flynn
and Wall. A more accurate approximation by Murray and White gives rise to B = 2
and C = 1 and leads to another popular equation that is frequently called the Kiss-
inger-Akahira-Sunose equation [ 33 ]:

β E

RT

i α

α

ln = Const − .

(2.13)

2

T

, i

α , i

Relative to Eq. 2.11, Eq. 2.13 offers a significant improvement in the accuracy of
the E ʱ values. According to Starink [ 32 ], even more accurate estimates of E ʱ can
be accomplished when setting B = 1.92 and C = 1.0008 so that Eq. 2.12 takes the
following form:

β E

RT

i α

α

(2.14)

ln = Const − 1 0008 . .

192 .

T

, i

α , i