PRODUCTION OF ROUNDED TI-HYDROXIDE AND AL-HYDROXIDE PARTICLES IN A TURBULENT JET BY COAGULATION-CONTROLLED GROWTH FOLLOWED BY RAPID COALESCENCE

Experiments were made to form titanium and aluminum hydroxide particle s in lab scale turbulent subsonic gas jets with nozzle diameters of 0. 2 to 0.4 cm. Small clusters formed by homogeneous nucleation near the nozzle and grew by coagulation as they flowed downstream. Electron mic roscopy showed that the particles were rounded and unagglomerated, ind icating that coalescence rates exceeded coagulation rates. The experim ents demonstrate a method for producing unagglomerated fine metal oxid e particles. Aerosol number concentrations and size distributions were measured ibr different nozzles, velocities, and positions in the jet using a Condensation Particle Counter and a Differential Mobility Anal yzer. Number concentrations were in the range 10(7)-10(10) particles p er cm(3) of gas. Size distributions were lognormally shaped with media n particle diameters of 10 to 100 nm and geometric standard deviations of 1.3 to 1.6. The median particle diameters were correlated by a sem iempirical expression which depended on the precursor vapor loading, a xial position and jet velocity. The expression can be used to design t urbulent jet particle generators. (C) 1998 Elsevier Science Ltd. All r ights reserved.