Synthesis and characterization of mechanically alloyed aluminum-based compounds as high energy density materials

A new type of metastable reactive powders for potential use as high energy density materials in propellants, explosives, and pyrotechnics was developed. These powders are intended to replace aluminum typically added to energetic formulations to increase reaction enthalpy and temperature. The new materials are metastable aluminum-based alloys, which enable achievement of substantially reduced ignition temperatures and accelerated bulk burn rates compared to aluminum. Titanium and lithium were used as alloying components. The materials properties and characteristics leading to their enhanced combustion performance were investigated. The powders were prepared using mechanical alloying and characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray spectrometer (SEM/EDX), and thermal analysis. Detailed ignition measurements were performed to identify the processes affecting ignition for the prepared metastable powders.;Al-Ti alloys were prepared with compositions ranging from Al0.95 Ti0.05 to Al0.75Ti0.25. Mechanically alloyed powders comprised solid solution of Ti and Al. Upon their heating, a number of subsolidus exothermic transitions were detected and assigned to formation of different modifications of Al3Ti. Three distinguishable oxidation steps were observed for the prepared alloys. The products formed at different oxidation stages were quantitatively analyzed by XRD. Ignition of mechanically alloyed Al-Ti powders was investigated experimentally for heating rates ranging from 3·103 to 2·10 4 K/s. It was shown that ignition was triggered by the exothermic formation of a metastable L12 phase of Al3Ti.;Al-Li alloys were synthesized with a fixed bulk composition of Al 0.7Li0.3. At short milling times, an intermetallic LiAl delta-phase was readily produced. At longer milling times, the LiAl phase disappears and a solid solution of Li in Al (alpha-phase) formed with as much as 10 at % of dissolved Li. Continuing milling resulted in the production of a uniform, x-ray amorphous phase. Kinetics of the exothermic processes of metastable relaxation in Al-Li alloys observed in thermal analysis was not found to directly correlate with the ignition kinetics. It was proposed that ignition in the prepared alloys was driven by selective oxidation of Li.