Silica is well known in the pharmaceutical industry as an excipient. While pure silica, SiO2, is common, there are silicates of calcium, magnesium, and aluminum that are widely used as anti-caking agents, glidants, opacifiers, and viscosity modifiers.
These silicas are considered bulk solids and come in many forms, including flakes, pellets, granules, and even nanoparticles. There is another class of silica excipients that are of interest in pharmaceuticals:
porous silica (poSi).
PoSi, as the name implies, is simply silica that has some level of pores throughout the solid body. These post materials are typically categorized by pore size, where silica with pores of less than 2 nanometers (nm) are considered microporous, and silica with pores 2 to 50 nm are mesoporous, and when the pores exceed 50 nm, they are called microporous. Sometimes the bulk of these three categories are more generally called “nonporous,” which indicates pores smaller than 100 nm. The pore size, as well as the level of porosity, are important to the silica’s functionalization and applications.