Sonochemical Preparation and Characterization of Ultrafine Chromium Oxide and Manganese Oxide Powders

Ultrafine powders of chromium oxide (Cr₂O₃) and manganese oxide (Mn₂O₃) have been prepared at room temperature by the sonochemical reduction of an aqueous solution containing ammonium dichromate [(NH₄)₂Cr₂O₇] and potassium permanganate (KMnO₄), respectively. The yield of the sonochemical reduction has been enhanced by raising the reaction temperature or by using an aqueous solution of ethanol (0.1 M). The solid oxide residue formed on insonation has been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), differential scanning calorimetry (DSC), elemental analysis, electron microscopy (TEM, SEM/EDX), powder density, particle size (adsorption and microscopy), and BET surface area measurements. The powders are nanosized (50-200 nm), and the surface area varies from 35 to 48 m²/g. The as-formed X-ray amorphous Mn₂O₃ and Cr₂O₃ powders were converted into crystalline form by heating them at 600 and 900 K, for 4 h, respectively.