Chemistry Reference
In-Depth Information
tem. Thus one can conclude that the kinetics of the initial stage of DINA decom-
position is characterized by two limiting activation energies:
E
187
.
5kJmol
−
1
≈
in
145
.
8kJmol
−
1
at maximum autocatalysis. The
corresponding expressions for the rate are
the absence of autocatalysis and
E
≈
35000
/
R
T
)[
s
−
1
] at
P
∞
≥
10
−
1
MPa
,
10
13
exp(
k
= 2
.
5
×
−
(10.14)
10
18
exp(
45000
/
R
T
)[
s
−
1
] at
P
∞
<
5
10
−
3
MPa
.
k
= 3
×
−
·
(10.15)
Strictly speaking, the true rate constant of the initial stage is determined by ex-
pression (10.15), since otherwise—see Eq. (10.14)—it is implied that some of the
decomposition products have accumulated in the system.
10.5.3 Macrokinetics of Heat Evolution During DINA
Decomposition: Thermal Explosion
The experiments used to study the critical conditions for DINA thermal explosion
at various pressures were carried out using the experimental setup schematically
shown in Fig. 10.4.
First, let us consider the qualitative characteristics of the process (Fig. 10.6). At
low pressures (
P
∞
= 5
10
−
3
MPa) the maximum sample warm-up value,
×
Δ
T
st
=
T
max
-
T
0
, does not exceed 5
.
3
◦
C. As
T
0
grows,
T
st
initially increases, reaching
its maximum value at
T
0
= 152
◦
C, and then it decreases, passing zero (at
T
0
=
179
◦
C), so the sample temperature under stationary conditions becomes lower than
the thermostat temperature
T
0
(
Δ
T
st
<
0).
The increase in the pressure results in a dramatic change in the situation. As
T
0
grows up to a certain value (
T
c
0
), the warm-up value increases monotonously.
Upon passing
T
cr
0
Δ
10
−
2
MPa
it increases very rapidly. For example, at
P
∞
= 2
×
and
T
0
= 145
.
5
◦
C
T
st
= 12 deg, and at
T
0
= 150
◦
C
Δ
Δ
T
st
= 28 deg. As
T
0
is in-
creased further,
T
st
reaches its maximum value and then decreases. As the pres-
sure increases up to
P
∞
= 4
Δ
10
−
2
MPa, this pattern becomes more pronounced:
×
at
T
0
= 143
.
5
◦
C
T
st
= 11
.
5 deg, and at
T
0
= 145
.
5
◦
C
T
st
= 47
.
5 deg. The life-
time of such high warm-ups is quite short (several minutes) and they reduce due to
burning-out. The conversion degree corresponding to the maximum
Δ
Δ
Δ
T
st
estimated
= 0
.
1-0.2. At
T
0
>
T
0cr
and
using the method proposed in [10] does not exceed
η
0
.
1 MPa, quasi-stationary warm-up growth ceases at some point. The warm-ups
in the system grow very rapidly, attaining very high values. The maximum warm-up
values can be recorded with high accuracy, while the process dynamics cannot be
followed by devices with response times of about 1 s (microgalvanometric amplifier
and electronic potentiometer).
In this case, due to the absence of the temperature distribution over the sample
volume (Bi
≥
P
1), the classic Semenov scheme can be applied to analyze the heat
evolution:
