Silicon dioxide is commonly called as silica. It occurs in several crystalline forms namely quartz, cristobalite and tridymite.
pure silicon dioxide
Systematic name : Dioxidosilicon
Molecular formula: SiO2
Density :2.634 g/cm3
Melting point :1650(±75) °C
Boiling point :2230 °C
SiO2 is a three dimensional covalent solid, in which each Si atom is tetrahedrally bonded to four oxygen atom and each oxygen atom is attached to two silicon atom by covalent bond .the entire crystal may be considered as a giant molecule.
Silica is relatively inert because of very high Si-O bond enthalpy .the important amorphous form of silica are silica gel and kieselguhr. Silica gel is used as drying agent, as a support for chromatographic material, catalyst and also used as humidity detector.
Uses of silicon dioxides
Silica is also used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes.
As hydrophobic silica it is used as a deformer component. In hydrated form, it is used in toothpaste as a hard abrasive to remove tooth plaque.
In its capacity as a refractory, it is useful in fiber form as a high-temperature thermal protection fabric