Preparation and Characterization of Silicon-Metal Fluoride Reactive Composites

Fuel-rich composite powders combining elemental Si with the metal fluoride oxidizers BiF₃ and CoF₂ were prepared by arrested reactive milling. Reactivity of the composite powders was assessed using thermoanalytical measurements in both inert (Ar) and oxidizing (Ar/O₂) environments. Powders were ignited using an electrically heated filament; particle combustion experiments were performed in room air using a CO₂ laser as an ignition source. Both composites showed accelerated oxidation of Si when heated in oxidizing environments and ignited readily using the heated filament. Elemental Si, used as a reference, did not exhibit appreciable oxidation when heated under the same conditions and could not be ignited using either a heated filament or laser. Lower-temperature Si fluoride formation and oxidation were observed for the composites with BiF₃; respectively, the ignition temperature for these composite powders was also lower. Particle combustion experiments were successful with the Si/BiF₃ composite. The statistical distribution of the measured particle burn times was correlated with the measured particle size distribution to establish the effect of particle sizes on their burn times. The measured burn times were close to those measured for similar composites with Al and B serving as fuels.