Sustainable Pyrotechnics: Combustion Behavior of B₄C/Bi₂O₃ for Delay Compositions

Understanding the combustion behavior of greener pyrotechnic delay compositions is key to developing more sustainable and efficient materials for practical applications. This study explores B₄C, a high-reactivity fuel, and Bi₂O₃, an efficient oxidizer, as eco-friendly alternatives to traditional formulations. Thermodynamic calculations guided formulation design, predicting major combustion products. After formulation, the compositions were granulated, pressed at varying pressures (64-385 MPa), burned, and analyzed for their burning rates. Results show that increasing compaction leads to a progressive decrease in burning rates, as reduced porosity shifts combustion from convective to conductive. Particle size influences combustion up to a certain limit, while the granule size of the final composition alters the burning profile. The reaction unfolds in multiple stages, starting with a solid-solid preignition phase, then moving to a solid-liquid phase, and eventually reaching a gas stage. Complementary analyses of solid residues and combustion gases supported the proposed reaction pathway. These findings provide crucial insights into optimizing both performance and environmental impact reinforcing the viability of B₄C/Bi₂O₃ formulations for practical applications.