Highly reactive spheroidal milled aluminum

Abstract

Mechanical milling of aluminum powders with two immiscible liquids, acetonitrile and hexane, produced roughly spherical aluminum particles with increased flowability and sizes in the range of tens to hundreds of microns and specific surface areas of 15 – 30 m2/g. The particles with near spherical shapes comprised agglomerated aluminum flakes. Samples were milled from 0.5 to 2 hours in a planetary mill. Longer milling times led to reduced sizes, while porosity and specific surface area peaked at intermediate times. Thermal analysis showed that samples heated in an oxidizing environment oxidized faster than nonporous micron-size aluminum, with oxidation rates comparable to those of nanopowders. The active aluminum content of these powders was comparable to that of micron-sized aluminum. Reaction steps and respective activation energies were consistent with other aluminum powders. However, unlike regular micron-sized aluminum, the spheroidal milled powders placed on a surface heated electrically at 3500 K/s ignited at temperatures ranging from 750 to 900°C. Ignition temperatures decreased with longer milling times and decreasing particle size. In low-temperature, humid environments, the spheroidal milled powders lost about half the active aluminum content compared to nonporous reference Al powders aged under identical conditions. Heterogeneous reactions in the prepared powders are interpreted using a model comprising a reactive shell and an inert core.