VOLATILE METAL-OXIDE EVAPORATION DURING AEROSOL DECOMPOSITION

The role of particle evaporation during synthesis of volatile metal ox ide powders (Bi2O3, MoO3, PbO, and V2O5) by aerosol decomposition (spr ay pyrolysis) in a heated how reactor was investigated. Solid particle s (0.1-0.6 mu m) of predominantly beta-Bi2O3 mere formed with smooth s pherical shape at all reactor temperatures (673-1173 K) employed. Soli d MoO3 particles (0.1-1.2 mu m) produced at low temperatures (673-773 K) had a roughly spherical or faceted morphology and at high temperatu res (873 K) had a platelike or layered structure. Solid V2O5 particles produced at low temperatures (573-673 K) mere spherical and at high t emperatures (973-1073 K) were platelike. The PbO particles were solid and spherical for all temperatures studied (773 degrees-1073 degrees C ). Evaporative losses of up to 100% to the reactor walls were observed for all the metal oxides, due to their substantial vapor pressures. T he evaporative losses mere modeled by considering simultaneous particl e evaporation and mass transfer of the metal oxide vapor to the reacto r walls. The calculations indicated that, for most of these volatile m etal oxides, evaporative losses mere limited by diffusional transport of the vapor to the reactor walls and that evaporative losses occur wh en the vapor pressure of the oxides in the reactor is above 10(-5)-10( -3) mm Hg.