AN AEROSOL CHEMICAL REACTOR FOR COATING METAL OXIDE PARTICLES WITH (NH4)2SO4-H2SO4-H2O__PART 2: MANIPULATION OF THE METAL OXIDE CORE

The complex chemical and morphological character of atmospheric particles challenges laboratory scientists to produce and study similar particles. In this paper, spray pyrolysis methods are adapted for the production of aerosols of hematite ((alpha)-Fe2O3), corundum ((alpha)-Al2O3), mullite (Al6Si2O13), and amorphous silica (am-SiO2). The particle mode diameter and the total number concentration vary from 30 to 300 nm and 105 to 107cm^-3, respectively, when the precursor concentrations are adjusted from 100 µM to 1M. The precursors include FeCl3·6H2O, Al(NO3)3·9H2O, and Si(OCH2CH3)4, which are nebulized and flowed through a tube furnace at 1200°C. Single-crystal hematite and mullite and polycrystalline corundum result. Decomposition products from Al(NO3)3·9H2O include NO(g) and NO2(g). Methanol, which is the precursor solvent for mullite and silica, thermally decomposes to yield several gases, including H2O, CO, CO2, CH4, C2H2, and C2H4. In a separate tube furnace incorporated in the aerosol flow stream, the oxide particles are coated with sulfuric acid, which is subsequently neutralized by NH3(g).