Chemistry Reference
In-Depth Information
Chapter 2
Methods for the Experimental Study of
the Linear Pyrolysis of Condensed Materials
Abstract
Original instruments for measuring rates of linear pyrolysis (the stationary
one-dimensional propagation of the reaction front in condensed compound thermal
decomposition) are described. Kinetic constants of the fast high-temperature de-
compositions of polymers and inorganic materials (which cannot be obtained using
isothermal kinetic methods) can be calculated from the experimental data provided
by them. These instruments were used to study the burning mechanisms of modern
solid rocket propellants over wide heating temperature ranges (up to 900
◦
C) and
pressures (100 Pa-3 MPa). An instrument called the “chemical arc” is described for
the first time. In the chemical arc, the high-temperature linear pyrolysis of solid pro-
pellant components (polymer and oxidizer) occurs in the stationary burning mode
under the influence of the flat flame of interaction between the gaseous products of
linear pyrolysis.
2.1 Equipment for Studying Linear Pyrolysis on a Hot Plate
at Pressures
P
∞
=0
.
1
kPa-3 MPa
A schematic of the LP-1 installation used to study linear pyrolysis on a hot plate at
pressures in the range 0.1 kPa-0.1 MPa is shown in Fig. 2.1.
Hot plate
1
is mounted on copper rods
2
fixed on a bulky vinyl plate. The hot plate
(heater) should be made of a material (metal or alloy) with a high melting point,
such as nichrome, stainless steel or niobium. In some experiments (see Sect.
??
), the
heater and a sample were separated by a thin layer of mica (5-10
m) to eliminate
the catalytic effect of the heater material on the kinetics of the linear pyrolysis.
A Pt/Pt-Rh thermocouple (50
μ
m in diameter) is spot-welded to the center of the
heater (just above the sample). The sample (
3
) is fixed at the end of a steel cylinder
4
which slides along a guiding Teflon rod
5
. The sample is pressed onto the heater by
a load
6
which is connected to the steel cylinder (
4
) by a Capron thread that passes
over a pulley fixed onto an axle. During linear pyrolysis, rotation of the pulley causes
chopper
7
, mounted onto the same axle as the pulley, to rotate. A conical gear with a
mirror
10
for measuring low rates of linear pyrolysis is fixed to the other end of the
μ
