Aluminum Nanoparticle Production by Acetonitrile-Assisted Milling: Effects of Liquid- vs Vapor-Phase Milling and of Milling Method on Particle Size and Surface Chemistry

Milling aluminum balls together with either vapor- or liquid-phase acetonitrile (ACN) leads to production of nanoparticles by mechanical attrition; however, vapor-phase ACN is far more efficient at inducing size reduction, leading to more, smaller, and more uniform particles. The attrition process is also more efficient than traditional milling of particulate starting material and produces nanoparticles with substantially lower contamination levels. This paper is aimed at better understanding the nature of the size reduction process, the chemistry driving it, and the particles it produces. Mass spectrometry was used to probe gases generated during milling, and a combination of X-ray photoelectron spectroscopy, infrared spectroscopy, dynamic light scattering, helium ion microscopy, scanning electron microscopy, and thermogravimetric analysis/mass spectrometry was used to probe the particles and their surface layer. To provide further insight into the chemistry occurring between ACN and aluminum under milling conditions, high-level ab initio theory was used to calculate the structures and energetics for binding and reactions of ACN and its fragments at different sites on an Al 80 model surface.