The synthesis and characterization of aluminum nanoparticles passivated with epoxides and graphite and the modeling of size-dependent enthalpy of reaction.

摘要

Aluminum nanoparticles (Al NPs) show great promise for a variety of high-energy applications. Two problems exist in synthesizing Al NPs: kinetic instability to grain growth and oxidation. Therefore, a capping agent must be introduced to passivate the Al NPs. This thesis presents two passivation schemes. One reaction scheme is to use the Al NP to polymerize alkyl-substituted epoxides to produce a polyether passivating layer. Fourier transform infrared (FTIR) and carbon-13 nuclear magnetic resonance (NMR) show that a polyether is created. Powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) show the presence of ∼15 nm particle with a ∼7 nm thick polyether layer. Hydrogen gas emission and back-EDTA titration shows that the air stability of the material depends on the size of the alkyl-substituent chain of the epoxide and the moisture content in the air. The larger substituent chain of epoxydodecane protects the Al NP core better than epoxyhexane and epoxyisobutane, and epoxyisobutane-capped Al NPs are pyrophoric. Differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) shows that the Al NPs capped with epoxydodecane combusts completely unlike the Al NPs capped with epoxyhexane. Of what is reported to date, Al NPs capped with epoxydodecane have the highest air stability of any organically-capped Al NPs by over an order of magnitude. The 10:1 and 5:1 Al NPs capped with epoxydodecane have active Al content over 90% when exposed less than 30 minutes.;The other reaction mechanism uses graphite to coat the Al NPs. Initially, a self-assembled monolayer (SAM) of dodecylamine is developed on the surface of Al NPs. Then, the resulting nanopowder is sealed in a glass tube under vacuum and heated at 550 °C for 12 h. During the roasting process, the SAM pyrolyzes into graphite. FTIR shows no observable peaks for the Al NPs capped with dodecylamine roasted at 550 °C. The metallic Al content is lower and attributable to a layer of aluminum nitride.;This thesis also discusses a model describing the particle size dependence of the oxidation enthalpy of the Al NPs. The model includes the size dependence of the reactant nanoparticles, the size dependence of the product lattice energy, extent of product agglomeration, and surface capping agents. The strongest effects on Al NP energy release occur for particle diameters below 10 nm, with enhanced energy release for agglomerated oxide products and decreased energy release for nanoscale oxide products.