Constant volume explosions of aerosols of metallic mechanical alloys and powder blends

High-energy ball milling was used to prepare sets of mechanical alloys in the systems Al-Mg, Al-Mg-H, B-Mg, and Ti-B. X-ray diffraction, electron microscopy, and low-angle laser diffraction were used to characterize structures, morphology, and sizes of the alloys, respectively. The produced materials were metastable and nanocrystalline; the particle sizes were in the range of 1-50 mum. A constant volume explosion technique was used to evaluate performance of the mechanical alloys and to compare it to the performance of blends of elemental powders of the same bulk composition. For reference, samples of mechanical alloys were annealed to produce stable intermetallic phases and tested in the same explosion experiments. Pressure traces recorded in real time served as the main piece of experimental information. After selected experiments, combustion products were collected and analyzed. The results have shown that the combustion rates of mechanical alloys are appreciably higher than those of the respective powder blends, thermodynamically stable intermetallics, and pure metals. The analyses of the combustion products also showed that combustion was more complete for mechanical alloys. It was found that combustion parameters of mechanical alloys compared to other metallic fuels were significantly improved even though their particle sizes were identical or greater than those of the reference metals. The use of mechanical alloy powders with relatively large particle sizes is expected to be advantageous in many practical applications requiring mixing and handling of energetic formulations.