Pyrotechnic heater setup as a calorimeter: Micro- vs. nano- Mg/Fe2O3 thermites

Abstract

Combustion of thermite composition Mg/Fe2O3 with micron- and nano-sized components was studied in pyrotechnic heater setup. Pressed charges were burned out in hermetic steel tubes with simultaneous pressure and temperature registration. Advanced system of thermocouples connections allows drawing thermal maps of the steel case heating with high spatial and temporal resolution. Mathematical processing of raw thermal data gives the temperatures for thermite combustion. Initial temperature and setup orientation (either vertical or horizontal) show almost no influence on combustion temperature. Nanothermite produces in 500 K lower temperatures compared to micron-sized composition, apparently due to lower metal content in nano-Mg. Comparison of the experimental data with thermodynamic calculation output shows important differences in the combustion temperature and composition of products. Adiabatic temperature predicted is slightly lower than experimental and this fact is linked with formation of spinel MgFe2O4 phase, not accounted in computations. Thus, utilization of the pyrotechnic heater setup gives valuable information not only about pressure and porosity effects, but also about combustion temperature, composition of products and process mechanism.