Charging and coagulation during flame synthesis of silica

Morphology and surface properties of fumed silicas

“…Equation (8) was solved using a regularization procedure assuming that normalized desorption and residual coverage are bounded by the equation…”

“…Features of the lower amount of water adsorbed under standard conditions in comparison with porous silica gel because primary particles of fumed oxides are nonporous; (vii) possibility of decomposition of secondary particles to primary ones under specific treatments, e.g., in aqueous suspension, if binding of primary particles occurs with no formation of the siloxane bridges (this could be controlled by synthesis conditions); and (viii) formation of stable concentrated aqueous suspensions characterized by very slow sedimentation [1][2][3][4][5][6][7][8][9][10][11][12][13]. Thus this set of the characteristics of fumed silicas is very impressive.…”

“…The specific surface area (S BET ) of fumed silicas produced by burning of SiCl 4 in an O 2 /H 2 /N 2 flame can be varied over a large range at S BET = 50-500 m 2 /g dependent on such synthesis conditions as the temperature map in the flame, the flame length, the flow turbulence and velocity, and the ratio of reactants [1][2][3][4][5][6][7][8][9][10][11][12][13]. Features of the lower amount of water adsorbed under standard conditions in comparison with porous silica gel because primary particles of fumed oxides are nonporous; (vii) possibility of decomposition of secondary particles to primary ones under specific treatments, e.g., in aqueous suspension, if binding of primary particles occurs with no formation of the siloxane bridges (this could be controlled by synthesis conditions); and (viii) formation of stable concentrated aqueous suspensions characterized by very slow sedimentation [1][2][3][4][5][6][7][8][9][10][11][12][13].…”

Coagulation of bipolarly charged ultrafine aerosol particles

“…In their theoretical study, Xiong, Pratsinis, and Mastrangelo (1992) showed that it is possible to considerably reduce the average particle size and narrow the particle size distribution by introducing unipolar charges during gas-phase particle formation. Vemury and Pratsinis (1996) investigated the effect of corona charging during flame synthesis of silica particles and showed that the primary particle size decreases with increasing field strength. Borra et al (1999) presented a new process where the controlled coagulation of droplets produced by electrosprays is achieved through electrical forces.…”

Thermal equilibration of soot charge distributions by coagulation

“…Low frequency AC electric fields were examined by Koizumi, Kawamura, Tochikubo, and Watanabe (2000) as a means to enhance coagulation and thereby increase the electrostatic precipitator efficiency for sub-micron particles. Vermury and Pratsinis (1996) explored the use of particle charging, with needle and plate electrodes, to control growth rates during flame synthesis of silica particles. A detailed study by Katzer, Weber, and Kasper (2001) concluded that electric fields play predominantly a secondary role in particle growth, for example, via changes in local flame temperature.…”