Synthesis of reactive Al/Ni structures by ball milling

Material systems that exhibit self-propagating exothermic reactions (SPER) can be potentially used for nano/microscale heater purposes in thermal nanomanufacturing applications. We propose that ball milling (BM) is a simple and cost effective technique that can be used to produce such materials. For this purpose, an interrupted BM run of aluminum/nickel powders with a molar ratio of 1:3 was performed, followed by the cold pressing of the powders into pellets that were ignited using an external heat source. Samples that exhibit SPER were characterized before and after ignition using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) with a Back Scattered Electron Detector (BSE), Energy Dispersive X-Ray analysis (EDX) and Differential Thermal Analysis (DTA). The results show that after 7 h of BM an aluminum/nickel lamellar structure forms at the particle boundaries. The characteristic lamella dimension reduces with increasing milling time down to ∼200 nm after 10 h of BM. The ignition conditions for compacts of milled powders indicate that samples with a higher volume fraction of the lamellae possess the shortest ignition time at 4.25 s.