Chemistry Reference
In-Depth Information
10
−
2
sdeg
−
2
. However, the linearization
of the experimental results in these coordinates does not completely prove the cor-
rectness of Eq. (5.6). The quantitative analysis of the parameters of the straight line
appears to be of significant importance. The absolute values of these parameters
that are strongly dependent on
Qk
0
,
E
and
T
0
cannot be estimated from Eq. (5.6)
with the required accuracy. In order to quantitatively compare the theoretical and
experimental data, the ratio
10
−
2
sdeg
−
1
,
b
= 2
.
3
where
a
= 1
.
6
×
×
= 8
R
T
a
b
E
, which is independent of
Qk
0
and slightly
(not exponentially) dependent on
E
and
T
0
, can be used. For
E
= 202 kJ mol
−
1
[12],
b
theor
= 82
◦
and
b
exp
= 70
◦
, which indicates a satisfactory agreement between
the theoretical and experimental data.
The kinetic parameters
Qk
0
and
E
can also be determined from the experimental
data using Eq. (5.6). Let's rewrite this expression as
= lg
c
Qk
0
1
.
6 + 0
.
2
E
R
+
E
lg
e
R
t
ign
T
0
−
T
0
−
T
∞
1
T
0
.
lg
(5.8)
T
0
T
∞
t
ign
T
0
−
against
T
−
0
is lin-
ear, and
E
can be found from the slope ratio and
Qk
0
from the intercept on the
y
-axis. Under regular experimental conditions,
T
0
−
T
∞
If
is kept constant in the experiments, a plot of lg
T
0
T
∞
T
0
−
T
changes only slightly; for ex-
ample, in the case of experiments with nitrocellulose samples at
T
∞
= 293-298 K
and
T
0
= 485-515 K, it varied by 5%. Thus, this approach can be used to analyze
experimental data obtained when
T
0
∞
T
0
const and
T
∞
= variable. This is very con-
venient, since if the initial sample temperature is equal to the room temperature, an
additional thermostat (
5
, Fig. 5.1) is not needed. Experimental data obtained for the
indicated range of
T
0
are presented in Fig. 5.3 (each point corresponds to a
t
ign
value
that is the average from three/four experimental runs). The good agreement between
the data obtained for samples of different diameters implies that
t
ign
is independent
of the lateral heat losses. Analysis of the data shown in Fig. 5.3 using Eq. (5.8) gave
≈
ign
.
.
Fig. 5.3
Arrhenius
anamorphosis presentation
of the experimental data
showing the dependence of
the ignition delay,
t
ign
,onthe
block temperature,
T
0
,at
T
∞
=
293-298 K for the samples
12 mm (
circles
) and 18 mm
(
squares
) in diameter
.
.
.
.
