What Is Silicon Dioxide?
Silicon dioxide, also known as silica, is a compound of silicon and oxygen.
It occurs naturally in several forms, including quartz, scaly silica stone, and cristobalite. Quartz is the most prevalent, making up about 12% of the Earth’s crust. Beyond minerals, organisms such as diatoms and some sponges use silicon dioxide for their skeletons or shells, and it is also found in certain plants like some ferns and grasses.
Uses of Silicon Dioxide
Silicon dioxide is utilized in various applications, including:
1. Silica Glass
As silica glass, silicon dioxide is used in analytical cell materials, semiconductor manufacturing, and optical fibers. It is valued for its purity, heat resistance, broad light transmission range, and resistance to acid and alkali attack.
2. Silica Gel
Silica gel, derived from silicon dioxide, is a popular moisture absorbent used as a desiccant, particularly in food preservation.
3. Silica Particles
Depending on their shape, size, and porosity, silica particles find use in cosmetics, HPLC columns, and as coating agents. Colloidal silica, water or solvent-dispersed silica particles serve as an abrasive.
4. Fumed Silica
Fumed silica is a white, low-density powder produced by flame hydrolysis of silicon tetrachloride or by decomposing water glass with inorganic acid. It is a rheology modifier.
5. Silica Aerogel
Silicon dioxide aerogel, a highly porous material, consists mostly of air and is transparent due to its fine particle network and small pore size. It is an effective insulator and is made by hydrolyzing tetraethoxysilane (TEOS) in a solvent, followed by supercritical drying.
Properties of Silicon Dioxide
With the formula SiO2 and a molar mass of 60.08, silicon dioxide is used in glass and ceramics for its high heat and corrosion resistance. It reacts with hydrofluoric acid to form hexafluorosilicic acid (H2SiF6).
Types of Silicon Dioxide
Silicon dioxide exists in several crystal forms, based on different arrangements of the SiO4 tetrahedra, which influence its stability under varying conditions.
1. Cristobalite
A cubic or octahedral crystal with a structure similar to diamond when considering only the Si atoms.
2. Tridymite
Hexagonal plate-like crystals with high and low-temperature forms; the latter has a slightly altered lattice.
3. Quartz
Exists as high-temperature hexagonal pyramidal crystals and low-temperature hexagonal columnar crystals. The latter is known as quartz crystal when well-formed.
4. Coesite
Monoclinic crystals, resistant to concentrated hydrofluoric acid erosion.
5. Stishovite
A tetragonal crystal with a rutile-type structure.
More Silicon Dioxide Information
Silicon Dioxide as a Raw Material for Glass
Silicon dioxide is the primary component of soda-lime glass, used widely in buildings and vehicles. It is sourced from silica sand, with soda ash or lime added to reduce the melting temperature and stabilize the glass.