  The combustion delay mixture of tungsten (W), potassium perchlorate (KClO4),
and barium chromate (BaCrO4), also known as the WKB mixture, has long been
considered to be an integral part of military-grade ammunition. Despite its
long history, however, their progressive reaction dynamics remains a question
mark, especially due to the complex nature of their combustion reaction. As
opposed to a one-step oxidation commonly observed in conventional combustions,
the WKB mixture is associated with a multibody reaction between its solid-state
components. To this end, the emergence of three combustion peaks, which we
corresponded with disparate chemical reactions, was observed using
thermogravimetric analysis on two separate WKB mixtures with differing mixture
ratios. We applied the stepwise isoconversional method on each of the peaks to
match the combustion chemistry it represents to the Sestak-Berggren model and
computed the conceptual activation energy. Further plotting the logarithmic
pre-exponential factor as a function of the reaction progress, we demonstrate a
method of using the plot as an intuitive tool to understand the dynamics of
individual reactions that compose multi-step chemical reactions. Our study
provides a systematic approach in visualizing the reaction chemistry, thereby
strengthening the analytical arsenal against reaction dynamics of combustion
compounds in general.
