The mechanism of the antimony/potassium permanganate combustion reaction
Results of a detailed thermoanalytical study of the
reactions in the antimony/potassium permanganate system,
which has been in use for many years as a delay
composition, are presented.
The starting points for such a study were the
investigation of the thermal decomposition of KMn04,
and the oxidation characteristics of the antimony as
well as the thermal analysis of the oxides of antimony.
Thermal decomposition of freshly prepared crystals
and finely powdered KMnO4 were studied utilising
thermogravimetry, differentia scanning calorimetry and
hot stage microsocopy techniques, under atmospheres of
air, nitrogen and argon. Data obtained from both TG
and DSC analysis were used to measure the non-isothermal
decomposition kinetics of KMnO 4- The activation
energy was calculated applying a number of different
methods, and the results were compared with the
isothermal evaluation of activation energy.
The decomposition of single crystals of KMn04 was
observed under a hot-stage microscope with a particular
interest in the fragmentation process, and the mechanism
of the decomposition reaction is discussed.
The gas-solid oxidation of antimony in air was
carried out by both DSC and TG methods. The results
revealed a two stage oxidation process corresponding to
the surface and bulk oxidation of antimony particles.
The reactions of the Sb/KMnO4 systems were
investigated extensively in pelleted form as well as in
powdered form by the thermoanalytical methods.
The ignition reaction, 9 of Sb/KMn 04 mixtures were
observed by a microscope as the temperature of the
sample increased rapidly. The effect of atmosphere on
the occurrence of the ignition reaction was t4sted. On
the basis of the results obtained from thermal analysis
and the studies of the mixtures in compacted form,
conclusions on the mechanisms of the main propagation
reaction were drawn.