Morphology of oxide particles made by the emulsion combustion method

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X-ray diffraction. Hollow gamma-Al2O3 particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid alpha-Al2O3 particles. Hollow spheres were obtained also for TiO2, ZrO2, and Y2O3 by ECM of TiCl4, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe2O3, CeO2, and MgO from aqueous solutions of their corresponding nitrates.