Nearly Pure Aluminum Powders with Modified Protective Surface

Abstract

The thermodynamically predicted benefits of aluminum combustion are rarely achieved because of extended ignition delays associated with protective alumina layer, which is always present on the aluminum surface. This effort focuses on adjusting aluminum combustion dynamics by modifying its surface and structure. Aluminum is cryo-milled with cyclooctane. The prepared material consists of micron-sized, equiaxial, nearly pure Al particles; their external surface and crystal grains are coated with a cyclooctane-modified layer with properties significantly different from those of regular alumina. The material's oxidation kinetics, as observed from thermo-analytical measurements, is different from that of pure aluminum. The powder ignites at substantially reduced temperatures, and produces shorter ignition delays and higher aerosol burn rates compared to a regular spherical Al powder with similar particle sizes. In air, single particles of the prepared composite material burn longer than pure Al and produce reduced molecular AlO emission, but generate nearly the same temperature as pure Al. In the combustion products of an air-acetylene flame, composite particles burn faster than pure Al.

Keywords:

• Ignition
• Metal combustion
• Oxidation
• Particle combustion
• Surface modification

ACKNOWLEDGMENT

This work was supported by Defense Threat Reduction Agency.