Short Communication: A Geometrical Approach to the Structure of Noncrystalline Silica Precipitates

The structure of silica precipitates from solution may warrant examination from a viewpoint quite different from that applied to previous studies of silica glass from melt. An icosahedral model, instead of its conjugate form, a pentagonal dodecahedral type, is herewith proposed for the structure of a very basic particle 1–2 nm in diameter, which is larger than the size of a SiO₄ tetrahedron (about 0.5 nm in diameter). The model is regarded herein as a spherical, icosahedral cage composed of a fragmental sheet of polymerized SiO₄ tetrahedra oriented conforming to the surface structure of the icosahedron. The growth stage of the model "nucleus" is herein considered to comprise the formation of a concentric sheet structure that grows, however, to limited extents because of structural distortion. Beyond the size, further growth is in what may be called an essentially random array of the nucleus particles, which are found in places to be linked with each other to form varying shapes such as curved rod, ring, and concentric rings. The new perspective comes from the exploration of the basic structure of silica precipitates from solution.