The effects of Al content on mechanical properties, thermal reaction behavior, and ignition characteristics of Al-Bi₂O₃ thermite

For thermite-based energetic structural materials (ESMs), it is a key challenge to balance safety performance and energy output. In this paper, four kinds of Al-Bi₂O₃ thermites with different Al contents were successfully compressed as bulk materials. The mechanical properties of Al-Bi₂O₃ thermites under different strain rates were determined by quasi-static compression tests and split Hopkinson pressure bar experiments. Thermal reaction behavior of Al-Bi₂O₃ thermite was characterized by an oxygen bomb calorimeter and a synchronous thermal analyzer. The fracture and ignition process of Al-Bi₂O₃ thermite under dynamic loading was captured by a high-speed camera. The experimental results showed that the compressed Al-Bi₂O₃ thermite was a kind of elastic-brittle material with the ultimate stress ranging from 100.4 to 129.5 MPa. The strain-rate effect of all designed Al-Bi₂O₃ thermites was observed from 0.001 to 4500 s⁻¹. Thermal analysis showed that the reaction rate of Al-Bi₂O₃ thermite at an Ar atmosphere was faster than at an air atmosphere. It was determined that Al-Bi₂O₃ thermite with a higher Al content has higher reaction heat based on the oxygen bomb calorimeter results. The dynamic ignition period revealed that the ignition delay time and ignited whole zone time of Al-Bi₂O₃ thermite increased with the addition of the Al content, and the absorbed energy also increased. Therefore, Al powder could be a multifunctional additive in enhancing the mechanical strength, increasing total reaction heat, and improving the safety performance, which would provide valuable insights for designing thermite-based ESMs with specific mechanical properties and reaction parameters.