Combustion of Aluminum‐Metal Fluoride Reactive Composites in Different Environments

Abstract

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.

Preparation and Characterization of Silicon-Metal Fluoride Reactive Composites

“…Burn time-particle size correlation for 50Si•50BiF3 powder ignited in air by a laser. For comparison, similar correlations are shown for powders of 50Al•50BiF3 [20] and 50B•50BiF3 [23] obtained by arrested reactive milling.…”

“…These times were shorter than reported burn times for Al particles of the same sizes. The burn time distribution was correlated with the particle size distribution for 50Si•50BiF3; the correlation plot is presented in Figure 15 along with earlier results for other metal-metal fluoride composites obtained using the same data processing method [20,23]. Like Al and B-based composites using BiF3 as an oxidizer, 50Si•50BiF3 composite powder particles burn rapidly, with most burn times under 1 ms.…”

“…These times were shorter than reported burn times for Al particles of the same sizes. [20] and 50B•50BiF3 [23] obtained by arrested reactive milling.…”

“…The particle surface temperature during combustion is expected to be close to 2750 K (predicted to be the adiabatic flame temperature), sufficiently high for gasifying a significant fraction of the main combustion product SiO2. [20] and 50B•50BiF 3 [23] obtained by arrested reactive milling.…”

An Unexpected Method to Synthesize Fluorinated Derivative of ANPZ

“…Fluorinated functionalization is an attractive modification for energetic materials [10]. High dielectric constant and electron-withdrawing capability of fluorine leads to greater chemical resistance and hydrophobicity, which will affect the safety issues advantageously.…”