Kinetic study of the formation reaction of colloidal silica spheres in microgravity using aircraft

Polymerization reactions of colloidal silica spheres via the hydrolysis and dehydration processes of tetraethyl orthosilicate with ammonia and a tiny amount of water in ethyl alcohol have been studied in microgravity by the parabolic flights of a MU-300 rear-jet aircraft. Induction periods and polymerization rates are determined by fast-scanning transmitted-light-intensity measurements and the fast-scanning dynamic light-scattering method. Direct observation of the reaction mixtures is also made with a charge-coupled device video camera. Reproducible and reliable data are obtained in microgravity compared with those in gravity. Increases in the induction times and decreases in the polymerization rates are observed in microgravity compared with those in gravity. One of the main reasons for these observations is the fact that the translational Brownian movement of the reactants and/or product spheres is free from downward translational movement in microgravity. Very weak convection of the reaction suspensions in microgravity is another important factor.