Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, most commonly found in nature as quartz. In many parts of the world, silica is the principal constituent of sand. Silica is one of the most complex and abundant families of materials, existing as a compound of several minerals and a synthetic product. Notable examples include fused quartz, fumed silica, silica gel, opal, and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and components in the food and pharmaceutical industries. In most silicon dioxides, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atom (see 3-D Unit Cell). Thus, SiO2 forms 3-dimensional network solids in which each silicon atom is covalently bonded tetrahedral to 4 oxygen atoms. In contrast, CO2 is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule. SiO2 has several distinct crystalline forms but almost always has the same local structure around Si and O. In α-quartz, the Si–O bond length is 161 pm, whereas, in α-tridymite, it is 154–171 pm. The Si–O–Si angle also varies between a low value of 140° in α-tridymite up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°. Molten silica exhibits several peculiar physical characteristics similar to those observed in liquid water: negative temperature expansion, density maximum at temperatures ~5000 °C, and a minimum heat capacity. Its density decreases from 2.08 g/cm3 at 1950 °C to 2.03 g/cm3 at 2200 °C. If you are looking for high quality, high purity, and cost-effective Silicon dioxide, or if you require the latest price of Silicon dioxide, please feel free to email contact mis-asia.