Effects of solvent on powder characteristics of zinc oxide and magnesia prepared by flame spray pyrolysis

Zinc oxide (ZnO) and magnesia (MgO) powders were made by flame spray pyrolysis of zinc acetate and magnesium acetate, respectively, dissolved in methanol-water mixture. The product powders were characterized by nitrogen adsorption, infrared adsorption (IR), X-ray diffraction (XRD) and transmission electron microscopy. The effects of solvent on powder characteristics were examined by changing methanol content (X = 1-0.4) in the solvent. Polyhedral aggregates of nanoparticles were formed from the precursor solution with X = 1-0.6 for both ZnO and MgO syntheses, suggesting complete evaporation of the metal species and particle formation in the gas phase. Decrease of the methanol content to X = 0.4 lowered the spray flame temperatures, suppressing complete evaporation, resulting in a mixture of nanoparticles and large (e.q. > 100 nm) particles for both ZnO and MgO synthesis. On the other hand, the XRD and IR spectra indicated partial hydroxide formation for MgO synthesis, differed from ZnO synthesis. The reaction with water vapor in the combustion gas can be enhanced for MgO because of the larger Gibbs energy change for hydroxylation in MgO than in ZnO.