Chemistry Reference
In-Depth Information
In [13, 14], the complete set of equations describing the macrokinetics of exothermic
and endothermic decomposition upon linear heating was considered and the funda-
mental role of the degeneration parameter used in the thermal explosion theory (the
Todes number)
R
T
2
=
c
Q
E
γ
,
where
T
∗
is the critical temperature of the thermal explosion under stationary con-
ditions (that is,
T
= const), was quantitatively analyzed.
Some other results from [13] and [14] relating to thermographic studies of sys-
tems with high values of the degeneration parameter
γ
are discussed in the following
sections.
6.2 Methods of Equalizing the Temperature and Decreasing
Self-Heating: Mechanical and Thermal Dilution
Let us consider methods that ensure the correctness of the experimental data on re-
action kinetics obtained under programmed heating. As was mentioned above, com-
mercially available devices are not designed to study reaction kinetics. Therefore, in
the general case, one cannot clearly identify the heat exchange conditions between
the environment and the experimental cell based on its design. This complicates the
quantitative analysis of the experimental data and markedly decreases the accuracy
of the estimated kinetic parameters. Special approaches that are intended to improve
this situation are proposed in [7, 11, 15, 16, 17]. For example, in an experimental
study of the kinetics of reaction in solution [11], the liquid reacting system was vig-
orously stirred. This allowed the process to be described by a set of equations in
which averaged characteristics were used. For obvious reasons, this method cannot
be applied to solid materials, including components of composite solid propellants.
Another approach based on the use of an experimental cell characterized by very
weak heat dissipation into the environment is proposed in [7]. In this case, the tem-
perature distribution over the reaction volume is quite uniform for liquid and solid
systems. However, the use of this method does not exclude thermal explosion for
highly exothermal reactions and, hence, it does not widen the extremely narrow
range of measurable reaction rates.
A method of equalizing the temperature based on the use of very light samples
(several
g) cannot be considered to be universal. It cannot be applied to study the
kinetics of heterogeneous systems containing coarse particles (fractions of mm),
including composite solid propellants. However for the study of “liquid-fine solid”
systems that react with low heat release, a combination of the methods proposed in
[7] and [11] may be quite promising.
In [15, 16, 17] we proposed an approach that not only ensured low coefficients
of heat exchange between the sample and the thermostat, but that also equalized the
temperature and at the same time decreased the self-heating via significant ballasting
μ
