Spherical composite powders combining boron and 5 wt% polytetrafluoroethylene (PTFE) with particle sizes around 10 µm were prepared by emulsion-assisted milling (EAM). Powders were milled using either zirconia or steel balls and thus contained either zirconia or iron contaminations, respectively. The oxidation of the prepared powders was studied using thermal analysis. The ignition temperature was determined using an electrically heated filament. Prepared powders were blended with KNO 3 as an oxidizer and ignited using a CO 2 laser beam. The powders were also aerosolized and burned in a closed vessel. The results showed no effect of zirconia contamination on the powder reactivity, while the added iron caused a reduction in the oxidation onset temperature by ∼50°C. The added PTFE did not substantially affect the oxidation onset for zirconia-milled powders but did reduce their ignition temperature. The added PTFE, in the absence of iron contamination, led to a higher combustion temperature and a brighter incandescent plume for the laser-ignited powders blended with KNO 3 . In the aerosol explosion experiments, peak pressures and rates of pressure rise increased respectively by ∼5 and 20% for the EAM-prepared boron powders with PTFE added and no iron impurity.
Momtaz et al. (Wed,) studied this question.