Designing Metal Fuels for Custom Thermite Compositions

Thermites are combinations of metal and oxide powders that, when ignited, exothermically react to release tremendous amounts of energy that can be used in welding, pyrotechnic, and military applications. Past work explored thermites by altering the oxidizer, morphology, microstructure, or fuel to oxidizer ratio and typically used the traditional fuel of choice, aluminum. Recent research on combustion of various metals and the development of the machine learning (ML) algorithms enables one to accelerate design of custom thermites. Materials can be customized to increase the rate of energy release, target specific temperature, generate specific gases, or have a gasless reaction. This customization can be achieved by combining thermite and intermetallic reactions, generating tunable mixing scale distributions of fuel and oxidizer, and exploiting distributions of particle sizes, shapes, and porosities. Here, the effect of the combination of such metal fuels as aluminum and zirconium is explored on the microstructure and reactivity of thermites with CuO, Fe₂O₃, and TiO₂ oxidizers. Composite thermite powders are formed by arrested reactive milling, a high-energy ball milling technique. Materials are characterized through SEM imaging and X-ray diffraction to explore morphology, microstructure and phases to aid establishing structure-function-performance relationships. Differential scanning calorimetry is used to observe the low temperature reaction sequences and product phases that may be relevant to employ in the optimized ignition and combustion scenarios. Preliminary results show that in argon environments up to 1273K, samples with greater than 25 at% Zr have low-temperature exotherms likely due to the formation of aluminides prior to subsequent oxidation of aluminum. Prepared samples are ignited using an electrically heated wire in air. A 440-nm wavelength laser ignites small batches of the prepared thermites in a closed 17-mL chamber, operated from 1 to 760 torr. A CO₂ laser ignites similar samples in room air. Ignition delays, burn times, and pressures traces are recorded for the laser-ignited samples. Emission produced by the flame is explored spectroscopically. Condensed combustion products are collected and analyzed. This work will focus on tailoring thermite reaction by tuning metal fuel composition and microstructure. The key experimental data will be used by an ML algorithm to optimize the tunable material parameters and develop novel thermite formulations on demand.