Effect of Milling Temperature on Structure and Reactivity of Al-Ni Composites

摘要

Reactive Al·Ni composites are of interest for combustion synthesis, joining, and as components of energetic formulations. Mechanical milling is one of the most practical techniques used fortheir preparation. This study investigated the effect of ball milling at cryogenic temperatures on the reactivity and structure of the Al·Ni composites. Stoichiometric mixtures of Al and Ni powders were milled both at room temperature and in a vial cooled by liquid nitrogen. The products were characterized using SEM images of cross-sectioned particles, differential scanning calorimetry (DSC), and X-ray diffraction. Powders were ignited on an electrically heated filament. Cryogenically milled powders contained aluminum and nickel mixed on a finer scale compared to those prepared at room temperature. Ignition temperatures of the powders prepared at room temperature decreased as a function of the milling time; the cryogenically milled powder ignited at the lowest temperature among all samples. DSC traces of the cryogenically milled powder contained three exothermic peaks, while only two clearly resolved peaks were observed for the powders milled at room temperature. The activation energy was found as a function of the reaction progress from a model-free isoconversional processing of DSC traces; it was qualitatively different for early stages of the exothermic reaction for the powders prepared at different temperatures.