Production of rounded Ti- 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 particles 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 microscopy showed that the particles were rounded and unagglomerated, indicating that coalescence rates exceeded coagulation rates. The experiments demonstrate a method for producing unagglomerated fine metal oxide 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 Analyzer. Number concentrations were in the range 10(7)-10(10) particles per cm(3) of gas. Size distributions were lognormally shaped with median 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 semiempirical expression which depended on the precursor vapor loading, axial position and jet velocity. The expression can be used to design turbulent jet particle generators. (C) 1998 Elsevier Science Ltd. All rights reserved.