Silica
Authors: Flörke Otto W. , Graetsch Heribert A. , Brunk Fred , Benda Leopold , Paschen Siegfried , Bergna Horacio E. , Roberts William O. , Welsh William A. , Libanati Cristian , Ettlinger Manfred , Kerner Dieter , Maier Monika , Meon Walter , Schmoll Ralf , Gies Hermann , Schiffmann Dietmar 
Published: April 2008

Silica (SiO2) is a commonly occurring compound in nature. Various crystalline and noncrystalline silica minerals of inorganic and biogenic origin are known. Depending on temperature, pressure, composition of the precursor phases, etc., several different crystalline modifications are formed. Quartz is the most abundant and well‐known polymorph. Silica occurs as meter‐sized quartz crystals or as amorphous masses made up of submicroscopic crystallites having different microstructures or growth fabrics. In addition, synthetic polymorphs have been produced for which no natural counterparts exist. In industry, quartz sand and silica rocks are widely used as raw materials for production of glass, ceramics, and silicon. Single crystals of quartz are grown artificially for application as resonator crystals in clocks, communication technology, and computer electronics. Both natural and synthetic silica powders are used as fillers to improve the mechanical properties of plastics.

The article contains sections titled:

1.Silica Modifications and Products1.1.Occurrence and Geochemistry1.2.Si‐O Bond and Crystal Structures1.3.Crystalline Silica Phases1.3.1.Crystalline Silica Minerals1.3.2.Crystalline Nonmineral Silica Phases1.4.Noncrystalline Silica Minerals1.5.Colored Silica Minerals1.6.Silica Rocks1.7.Crystalline Silica Products1.7.1.Cultured Quartz Single Crystals1.7.2.Polycrystalline Silica Products1.8.Noncrystalline Silica Products2.Quartz Raw Materials2.1.Physical Forms and Occurrence2.2.Processing2.3.Uses3.Diatomites3.1.Introduction3.2.Formation, Composition, and Quality Criteria3.3.Occurrence and Mining3.4.Processing3.5.Analysis3.6.Storage and Transport3.7.Environmental and Health Protection3.8.Uses3.9.Recycling4.Colloidal Silica4.1.Introduction4.2.Structure of Colloidal Silica Particles4.3.Physical and Chemical Properties4.4.Stability4.5.Production4.6.Analysis and Characterization4.7.Uses4.8.Storage, Handling, and Transportation4.9.Economic Aspects5.Silica Gel5.1.Introduction5.2.Structure, Properties, and Characterization5.3.Production5.4.Uses5.5.Economic Aspects5.6.Legal Aspects6.Pyrogenic Silica6.1.Flame Hydrolysis6.1.1.Production Process6.1.2.Morphology6.1.3.Solid‐State Properties6.1.4.Surface Chemistry6.1.5.Surface Modification with Silicon Compounds6.1.6.Characterization6.1.7.Uses6.1.8.Industrial Hygiene and Safety6.2.Electric‐Arc Process6.3.Plasma Process7.Precipitated Silicas7.1.Introduction7.2.Production7.3.Properties7.3.1.Physicochemical Properties7.3.2.Surface Chemistry and Surface Modification7.3.3.Chemical Composition and Analysis7.4.Uses7.5.Industrial Hygiene and Safety8.Porosils8.1.Introduction8.2.Physical and Chemical Properties8.2.1.Zeosils8.2.2.Clathrasils8.3.Manufacture of Porosils8.3.1.Synthesis of Porosils8.3.2.Dealumination of Aluminosilicate Zeolites8.3.3.Formation of Melanophlogite9.Toxicology9.1.Experiences with Humans9.2.Animal Experiments