Kinetic analyses of colloidal crystallization in microgravity - aircraft experiments

Nucleation and growth processes in colloidal crystallization of silica spheres were studied in microgravity produced by parabolic flights of an aircraft. A continuous circulating type of stopped flow cell system was used, and the time-resolved reflection spectra were measured. The cell system is composed of a peristaltic pump, a column containing a mixed bed of ion-exchange resins and a quartz observation cell. They are connected to a PharMed tube in a closed circuit. Close-up observation with a CCD camera was made. Nucleation rates decrease in microgravity. Crystal growth rates of the face-centered cubic (fcc) lattices decrease in microgravity (0 G) by about 25% compared with those in gravity (1 G). One of the main reasons for the retardation is that the downward diffusion of spheres, which may enhance the inter-sphere collision, disappears in microgravity. No convection of the suspensions in microgravity is also important. (C) 1999 Elsevier Science B.V. All rights reserved.