Microgravity experiments on colloidal crystallization of silica spheres inthe presence of sodium chloride

Rate coefficients (k) in the colloidal crystallization of monodispersed sil ica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic Eights of an aircraft. Time-resolved reflection spect roscopy is made with a continuous circulating-type stopped-flow cell system . The ii values decrease as the salt concentration increases both at 0 and G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of th e salt lower than 2 x 10(-6) mol/l. The rates in flight at G are larger by 15% (maximum) compared with those at 1 G on the ground. The ii values obtai ned at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 x 10(-6) and 4 x 10(-6) mol/l sodium chlo ride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity.