Synthesis of Monodispersed Spherical Silica

Abstract

Conditions which lead to the formation of spherical silica particles of uniform size by the reaction of tetraalkyl orthosilicate in alcoholic solution with water in the presence of ammonia are described. A series of electron micrographs and pH measurements of the solution are observed during the hydrolysis. Numerous small particles having irregular shapes and particle sizes from 100 to 200 angstrom are observed in very early stages of the process. A part of the particles spontaneously gathered together followed by immediate coagulation. The aggre gates changed from irregular shape into perfect- spheres and grew larger by the exhaustible supply of the small particles in an instant.
Rapid decrease of pH at that tim e continued until the small particles disappeared. In the final step of the hydrolysis, slow growth of spheres are observed by the concentration of solu te Si(OH)₄ species on their surface. In the meanwhile, pH of the solution remained at a de finite value.