title: Rapid Aluminum Nanoparticle Production by Milling in NH₃ and CH₃NH₂ Atmospheres: An Experimental and Theoretical Study.
abstract: Ball milling of aluminum in gaseous atmospheres of ammonia and monomethylamine (MMA) was found to produce particles in the 100 nm size range with high efficiency. A combination of mass spectrometry, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis with mass spectrometric product analysis (TGA-MS), scanning electron microscopy (SEM), infrared spectroscopy, and dynamic light scattering (DLS) was used to study the particles and the chemical interactions responsible for particle production. To help understand the nature of the surface chemistry, high level quantum chemical calculations were performed to predict the structures and energetics for binding and reactions of NH3 and MMA on aluminum surfaces. Both NH3 and MMA react with aluminum under milling conditions, producing H2 and other gaseous products, and leaving the surfaces functionalized. The surface functionalization enhances size reduction by reducing the surface free energy and the tendency toward mechanochemical welding. For both NH3 and MMA, the particle cores are metallic aluminum, but the surface chemical properties are quite different. The ammonia-milled particles are capped by an AlNxOyHz layer ∼10 nm thick, which passivates the particles. The MMA-milled particles are capped with a thinner passivating layer, such that they are pyrophoric in air and react with N2 at elevated temperatures.
authors.affiliation: †Department of Chemistry, University of Utah, 315 S. 1400 E., Salt Lake City, Utah 84112, United States.
authors.forename: Brandon W
authors.initials: BW
authors.lastname: McMahon
authors.affiliation: †Department of Chemistry, University of Utah, 315 S. 1400 E., Salt Lake City, Utah 84112, United States.
authors.forename: Jiang
authors.initials: J
authors.lastname: Yu
authors.affiliation: ‡Propellants Branch, Rocket Propulsion Division, Aerospace Systems Directorate, Air Force Research Laboratory, AFMC AFRL/RQRP, 10 East Saturn Boulevard, Edwards AFB, California 93524, United States.
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Boatz
authors.affiliation: †Department of Chemistry, University of Utah, 315 S. 1400 E., Salt Lake City, Utah 84112, United States.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Anderson
keywords: aluminum; ammonia; milling; monomethylamine; nanoparticle synthesis