Identifying a combination of intermetallic and thermite reactions that result in a non-expanding compact

We investigate low gas generating, thermite formulations composed of ball-milled Al-Zr fuel and TiO₂ (anatase) oxide powders combined in a stoichiometric ratio. These thermite materials have applications as heat sources in confined geometries where gas generation and sample expansion would be detrimental. In this study, we identify the processing conditions that yield the most reactivity and the least expansion by changing milling conditions from single stage to dual stage milling to tune the thermite microstructure and by varying metallic fuel composition from Al to 3Al:Zr to Al:Zr. The loose powders milled in a single stage display better intermixing of Al, Zr, and TiO₂ compared to those milled in two stages, as well as lower Al melt temperatures and the formation of Zr oxides when heated slowly under Ar. All thermite powders containing Zr show a decreased ignition temperature compared to the Al:TiO₂ baseline sample. When uniaxially compacted and reacted, all TiO₂ thermites mixtures burned near their adiabatic reaction temperatures, and all single stage milled samples and dual stage milled Al-rich samples react with a flaking appearance, expanding up to 1.8 times the original compact size. In contrast, the dual stage milled, Al:Zr sample did not expand, had the slowest average burn rate at 1.6 mm/s, and displayed a unique two stage reaction front. We attributed this dual front to the initial reaction of Al and Zr and the formation of Al-Zr intermetallics, followed by the oxidation of these species. All samples containing TiO₂ reacted well below the boiling temperature of Al and the melting temperature of Zr, confirming condensed phase formation of Al and Zr oxides.