Question

How would you prove that a silica microsphere made by the Stobber process is actually spherical? What affect might deviations from an exact spherical shape have on crystallizing opals and their optical properties?

Answer 1

Spherical shape of silica microsphere can be proved by TEM ( Transimission Electron Microscope) analysis. By using this analysis we may know the diameter of particles and we can see the shape of the particle in TEM image.

      Effects which can deviate from an exact spherical shape of particles.

1. Depending on the particle formation mechanism in the sol - precipitation process a huge number of primary particles is first nucleated in the initial high supersaturated solution which called the induction period. After this particle induction period, any further primary particles generated under supersaturation are consumed for the growth of stable particles. In this case, the resulting particles in the product suspension were highly monodispersed in size and spherical in shape, But, if the generation of primary particles by supersaturation exceeds the consumption of primary particles for the growth of stable particles during sol - precipitation, new stable particles are spontaneously formed by the self -aggregation of the extra primary particles and this can deviate the size of particles.

2. Concentration of tetraethyorthosilicate (TEOS) can also effect the size and shape of particles.

3. Concentration of catalyst can also effect size and shape of particles.