Chemistry Reference
In-Depth Information
Fig. 3.7
Kinetics of the
high-temperature
decomposition of crosslinked
PMMA [analysis of data
shown in Fig. 3.6 by using
expression (3.4)]
tgϕ [ϕ ,s
]
-1
1. 3
1. 4
1. 5
k
= 10
12
.
5
±
1
.
0
exp
s
−
1
.
43000
±
3000
−
(3.5)
R
T
3.2.2 Linear Pyrolysis of Cylindrical PMMA Samples
in the Presence of a Gas Film
In the experiments with samples of linear and crosslinked PMMA (
l
= 50 mm,
d
= 6-12 mm), installations LP-1, LP-2 and LP-4 were used. As well as the heater
temperature,
T
0
, the sample diameter,
b
, and the pressing force,
W
, were varied in
the following ranges:
b
=(0
.
6-1
.
2)
10
−
2
m,
W
= 5-17 N.
The experimental data are shown in Fig. 3.8 as a plot of lg
U
against
T
−
0
(a
coordinate system used in previous works on linear pyrolysis). In the studied range
of
T
0
, Arrhenius linearization does not take place, and the degree of curve divergence
increases with increasing
T
0
and
U
. This agrees qualitatively with ideas regarding
the gas-film effect: the temperature drop across the gas film,
×
T
=
T
0
-
T
S
, and its
thickness,
Z
, increase with increasing
U
and
b
and decreasing
W
.
Δ
U
, m/s
U
, m/s
0.9
1.0
1.1
1.2
1.3
1.1
1.2
0.9
1.0
1.3
b
Fig. 3.8
The influence of the sample diameter,
b
, and the pressing force,
W
, on the linear pyrolysis
of cylindrical samples of linear PMMA: (
a
)at
b
= 1
.
2
10
−
2
mand
W
= 16
.
5N (
1
), 12.3 N
(
2
) (points 2' correspond to the niobium plate), 9.9 N (
3
), 5.5 N (
4
); (
b
)at
W
= 16
.
5N and
b
=
1
.
2
×
10
−
2
m(
1
), 1
.
0
10
−
2
m(
2
), 0
.
8
10
−
2
m(
3
), 0
.
6
10
−
2
m(
4
)
×
×
×
×
