DISPERSIBILITY OF FUMED SILICA IN SIMPLE MEDIA

Dispersion of fumed silica powders having specific surface areas (S(BE T)) of 50-500 M2.g-1 was investigated based on the optical absorption (T) in the wavelength (lambda) range of 460-700 nm. Light scattering i ndex (n) was evaluated by using the equation tau = alambda(-n). In the fumed silica-water disperse system, n and tau at lambda = 700 nm chan ged rapidly to reach n and tau*700 nm, respectively, in the steady st ate under strong ultrasonic agitation conditions. n and tau*700 nm we re found to be more useful than S(BET) as a dispersibility index of fu med silica. In general n tended to increase as S(BET) increased, indi cating that aggregated silica particles became finer in water as the s ize of primary silica particles decreased. Dispersion behavior of fume d silica was also well correlated with tau700 nm. The fumed silica ha ving a larger tau700 nm easily reached an ultimate dispersion state i n water under mild ultrasonic agitation, while that having small tau7 00 nm started dispersion as rather grossy particles, which were subseq uently divided into finer pieces to reach a very fine dispersion state eventually. Fumed silica was dispersed similarly in other polar media such as methanol and acetone but not in nonpolar or poorly polar medi a such as n-hexane and toluene.