Enhanced reaction velocity and diluent homogenization in Redox Foils using arrested reactive milling thermite powder

Fully dense thermite foils, commonly referred to as Redox Foils, provide a unique opportunity to enable exothermic brazing of components by utilizing the molten metallic product of the thermite reaction as a braze. Due to the propensity of thermites to produce gas, however, Redox Foils must be diluted to eliminate metal vapor formation. This dilution can lead to foils that react too slowly to fully propagate in a bonding configuration, and therefore the reactivity of the foils must be improved. To do so, we milled the constituent powders (Al, Cu2O, and Cu) before we mechanically consolidated them into dense Redox Foils. The milling process decreases the reactant spacing, or the distance between the fuel (Al) and oxide (Cu2O), thereby enhancing oxygen transfer between the fuel and the oxide. Two fabrication strategies are employed: milling the thermite reactants (Al and Cu2O) without the Cu diluent, then adding the diluent before consolidation into Redox Foils, and the second is milling all components (Al, Cu2O, and Cu) together before consolidation. Both milling processes results in foils that propagate faster and release heat earlier than foils consolidated from unmilled, single-phase powders of Al, Cu2O and Cu, due to decreased reactant spacings. However, only the second milling strategy is capable of suppressing the production of Cu metal vapor during the reaction of the foils, as confirmed using emission spectroscopy. The lack of Cu vapor in these foils is attributed to a more uniform distribution of Cu diluent that is verified using digital analysis of foil microstructures.