Visualization of reaction chemistry in W-KClO4-BaCrO4 delay mixtures via a Sestak-Berggren model based isoconversional method

TL;DR

This study visualizes the complex multistep reaction dynamics of W-KClO4-BaCrO4 delay mixtures using a Sestak-Berggren model-based isoconversional method, revealing detailed insights into their combustion chemistry.

Contribution

It introduces a systematic approach to analyze and visualize multistep combustion reactions using isoconversional methods and the Sestak-Berggren model.

Findings

Identification of three distinct combustion peaks corresponding to different reactions.

Calculation of activation energies for each reaction step.

Demonstration of plotting pre-exponential factors to understand reaction dynamics.

Abstract

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.