Particle size distribution of spherical silica gel produced by sol-gel method

The sol-gel method was applied to the preparation of silica spherical powders, suitable for epoxy-molding compounds, with decreased thermal expansion coefficient, improved thermal conductivity and lowered shrinkage on curing. Tetramethyl orthosilicate, water and ammonia were mixed into sol solutions of a variety of compositions. A sample of 250 ml of each sol was dispersed in 500 ml of 1-butanol under stirring. After an hour of agitation by a magnetic stirrer, the dispersed sol droplets were gelled. The effect of parameters involved in the processing on the mean particle size D p and distribution index n was investigated. As a result, it was found that the wet gel particles were spherical and relatively narrow in particle size distribution, and D p and n varied depending on the composition and viscosity of sol and/or the rotation rate of the stirrer. It was also demonstrated that D p and n could be changed in the range from 22 to 42 μm and 1.7 to 2.2, respectively.