Propellants Explosives Pyrotechnics, Vol.44, No.10, 1327-1336, 2019
Combustion of Aluminum-Metal Fluoride Reactive Composites in Different Environments
Combustion of two nanocomposite powders comprising equal mass fractions of aluminum and a metal fluoride, BiF3 or CoF2, is characterized experimentally. The powders were prepared by arrested reactive milling; earlier work showed that they are readily ignited upon heating and are insensitive to ignition by electrostatic discharge. Here, powder particles were ignited in air by passing through a focused CO2 laser beam. They were also ignited and burned in oxygen-starved environments produced in the combustion products of an air-acetylene and air-hydrogen flames. Burn times and color temperatures of the particles were measured optically. Combustion products were collected and examined using electron microscopy. Correlations of burn times with particle sizes showed that the composites containing BiF3 burned faster than those containing CoF2. In air, the burn rates of both composite powders exceeded that of pure Al; in the oxygen-starved environments the burn rates of the prepared composites were comparable to that of Al. The flame temperatures of the CoF2-containing composite were limited by the Al boiling point while BiF3 containing composites burned at higher temperatures. Combustion mechanisms for the prepared materials are discussed qualitatively.