Chemistry Reference
In-Depth Information
Conclusion for Part I
The potential value of the experimental and theoretical results discussed in Part I for
the further development of ideas about the nature of the high-temperature decompo-
sition of energetic materials (in particular, composite solid and hybrid propellants)
is a matter of significant interest.
The spatially nonisothermal techniques of ignition and linear pyrolysis (which
allow one to obtain a certain essentially constant characteristic of the studied sys-
tem,
t
ign
or
U
, respectively) are considered to be “discrete” methods according to a
classification suggested in [1]. In the experiments the rates of the overall processes
are believed to be quite close to those of processes that occur in real solid-propellant
rocket engines and hybrid rocket engines. For example, the rate of polymer linear
pyrolysis performed in the LP installations reached a value of 10
−
1
cm s
−
1
.Thisis
quite close to the burning rates of hybrid propellants and only an order of magni-
tude lower than the linear pyrolysis rates characteristic of composite solid propellant
binders. The existence of the “third mode” of polymer linear pyrolysis (found for
PMMA at
U
>
5
10
−
2
cm s
−
1
) allows one to propose that similar macrokinetic
patterns occur for other polymeric fuel binders: a weak decrease in
T
S
at signifi-
cantly increased linear pyrolysis rates. The burning of polymer spheres was found
to obey the Sreznevsky law (the linear reduction in the surface area of a burning
polymer particle as a function of time:
d
2
=
d
0
−
κ
×
t
), which indirectly confirms
the existence of the third mode for fast linear pyrolysis. This leads to the resolu-
tion of the contradiction between data on high-temperature decomposition kinetics
obtained in early works on polymer linear pyrolysis [2, 3, 4] and burning rates and
surface temperatures as well as temperature profiles found for the condensed phases
of polymer-AP systems [5, 6, 7, 8, 9, 10]. Extrapolation of these experimental data
(by presenting the dependence of the linear pyrolysis rate on the surface temperature
in the form of an Arrhenius plot) to
U
1cms
−
1
resulted in unrealistically
high
T
S
values. In contrast, the
T
S
values determined for the third mode agreed
with the data obtained by microthermocouple measurements for the burning of bulk
PMMA in flowing oxygen [6, 11] and AP-PMMA mixtures [7].
In the chemical arc, linear pyrolysis of the components takes place in the flame
of interaction between the gaseous products of the oxidizer and fuel-binder decom-
position. Under these conditions, the burning occurs in one of its limiting modes
(in its “elementary act,” to be exact), which is an important stage in the complex
10
−
1
≈
−
