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Ultrafine spherical titanium, silicon, and aluminium oxide particles were prepared by the thermal decomposition of their alkoxide vapors, produced by evaporation and subsequent heating. High-concentration ultrafine particles having geometric mean diameters ranging between 0.01 and 0.06 pm and a geometric standard deviation of about 1.4 were obtained by varying the temperatures of the evaporator containing the liquid alkoxides and the reactor furnace, and the flow rate of carrier gas. For furnace temperatures lower than 400°C for TiO, and 1000°C for SiO, and AI,O,, the particles obtained were found to be amorphous. The observed changes in the particle size distributions due to changes in operating conditions were compared with those predicted theoretically by solving the discrete-continuous aerosol general dynamic equation accounting for coagulation and generation of monomer by thermal decomposition. The effect of monomer number concentration on the size distribution of generated particles was found to be qualitatively explained.

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