Mechanical activation (MA) of Al-based reactives has proven advantageous in modifying combustion behavior; however applying the same approach to Si-based reactives has been more challenging. In this work, we present a two-step mechanical activation process to prepare an activated silicon (Si)/polytetrafluoroethylene (PTFE) composite reactive powder. The two-step mechanical activation process consisted of first cryogenic milling, followed by high intensity milling at room temperature. This process resulted in particle refinement of the hard, brittle silicon particles and dispersion within the more ductile PTFE matrix. The resulting reactive powder was characterized for particle size distribution, morphology, powder X-ray diffraction (XRD), specific surface area (SSA), and combustion enthalpy. For the MA composite powder, no intermediate crystalline phases were detected by powder XRD. However, the measured combustion enthalpy was 15.6±0.4 kJ/g, which is 15.9% lower than the predicted heat of combustion of 18.6 kJ/g. The MA composite powder has a flake-like morphology with a bimodal particle size distribution (peaks at 79 μm and 479 μm). Surface area was found to be moderate at 1.75±0.06 m~2/g. The ductile nature of the resulting composite particles allowed for near full density pellets to be realized (98.5% theoretical maximum density) without additional binder. Combustion experiments showed that burning rates (from videography) ranged from 1.6 to 2.1 mm/s and combustion temperatures (from visual and infrared spectroscopy) ranged from 1708 to 1889 K. It was shown that these values had comparable performance to mixtures prepared with nanoscale and nanoporous silicon powders.
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