Ignition and Combustion of Al/Zr Composite Powders in Varied Gas Environments

It is well known that reactive metal composite powders can be ignited at relatively lower temperatures due to exothermic intermetallic formation reactions which help drive the particles to higher temperatures. This study systemically assesses the impact of intermetallic reactions contributing to particle ignition in three Al/Zr composite powders and differentiates its impact from oxidation and nitridation which may also influence ignition initiation.<br/> <br/>Here we synthesized three different shaker milled Al/Zr composite powders with varying Zr at% content: 3Al:Zr, Al:Zr, and Al:3Zr. After sieving particles below 75 microns, powder samples were heated to different temperatures at a slow heating rate (20C/min) in Argon based on initial DTA traces done to 1000C for each powder. Those samples were then characterized via XRD, DSC, TGA, and SEM to explain wire ignition results. Wire ignition experiments performed at heating rates between 15-25,000 K/s revealed that increasing Zr at% decreased the overall relative ignition temperature rise as all the intermetallic heat was removed.<br/> <br/>The combustion properties of the annealed powders were investigated to see if removal of the intermetallic heat affected the powder’s combustion behavior. A custom spectroscopy system called hyperspectral imager for emission and reactions (SHEAR) was used to gather key combustion data including combustion temperature profiles, burn durations and emission spectra. We relate this data to the microexplosion frequency and ignition delay of the three different powders.