From Si(OC2H5)4-NH3-H2O-C2H5OH system, monodispersed suspensions of spherical silica particles of colloidal size were prepared by means of hydrolysis of tetraethyl silicate.
Several attempts to produce silica spheres under the same experimental condition showed that a very narrow size distribution was always reproduced in each attempt, but it was not easy to obtain a constant median diameter.
In general, larger particles were grown during aging at a lower temperature and at a higher ester concentration, but these factors had no influence on their standard deviations.
An electron microscopic investigation of a series of samples were taken at different times from the same solution indicated that the spherical secondary particles were formed by coalescence of irregular shaped primary particles of a few hundreds Å diameter.
X-ray diffraction pattern showed that the spherical particles were amorphous just like a silica gel, and no crystallization has been observed even if they were heated at 1000°C for 7 hr in air. Although differential thermal analysis curve of the particles was the same as those obtained from silica gel, there was a slight difference in an amount of weight loss during heating, which might be attributed to a different amount of physically absorbed water.