Effect of composition and process control agents on the microstructure and ignition properties of ball-milled Al–Zr powders

We demonstarte the effect of varying Al-Zr chemistry on the morphology, microstructure, intermetallic reactions and ignition temperature of powders prepared using arrested reactive ball milling in hexane. Upon slow heating in Ar, 3Al:Zr, Al:Zr, and Al:3Zr (at.%) produces 19 ± 2.6 kJ/mol 22.0 ± 1.6 kJ/mol, and 14.0 ± 2.6 kJ/mol of heat respectively. When rapidly heated in air 3Al:Zr powders did not ignite, while Al:Zr and Al:3Zr had ignition temperatures of 461 ± 25 °C and 475 ± 25 °C, suggesting Zr oxidation is aiding ignition. To reduce cold welding of 3Al:Zr during milling, acetonitrile replaced a fraction of hexane. 3Al:Zr milled with 6.25 vol% and 12.5 vol% acetonitrile had smaller particles, higher heats and lower ignition temperatures compared to 0 vol%. 3Al:Zr with 6.25 vol% demonstrated the lowest ignition temperatures (433 ± 34 °C). 3Al:Zr with 12.5 vol% had the smallest mean diameter, largest surface area, smallest Zr inclusion areas, and highest heats, but had higher ignition temperatures (492 ± 27 °C), likely due to ZrC inhibiting the reaction of Zr with N and O.