Silica

Abstract

Silica (SiO 2 ) 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 Products 1.1. Occurrence and Geochemistry 1.2. Si‐O Bond and Crystal Structures 1.3. Crystalline Silica Phases 1.3.1. Crystalline Silica Minerals 1.3.2. Crystalline Nonmineral Silica Phases 1.4. Noncrystalline Silica Minerals 1.5. Colored Silica Minerals 1.6. Silica Rocks 1.7. Crystalline Silica Products 1.7.1. Cultured Quartz Single Crystals 1.7.2. Polycrystalline Silica Products 1.8. Noncrystalline Silica Products 2. Quartz Raw Materials 2.1. Physical Forms and Occurrence 2.2. Processing 2.3. Uses 3. Diatomites 3.1. Introduction 3.2. Formation, Composition, and Quality Criteria 3.3. Occurrence and Mining 3.4. Processing 3.5. Analysis 3.6. Storage and Transport 3.7. Environmental and Health Protection 3.8. Uses 3.9. Recycling 4. Colloidal Silica 4.1. Introduction 4.2. Structure of Colloidal Silica Particles 4.3. Physical and Chemical Properties 4.4. Stability 4.5. Production 4.6. Analysis and Characterization 4.7. Uses 4.8. Storage, Handling, and Transportation 4.9. Economic Aspects 5. Silica Gel 5.1. Introduction 5.2. Structure, Properties, and Characterization 5.3. Production 5.4. Uses 5.5. Economic Aspects 5.6. Legal Aspects 6. Pyrogenic Silica 6.1. Flame Hydrolysis 6.1.1. Production Process 6.1.2. Morphology 6.1.3. Solid‐State Properties 6.1.4. Surface Chemistry 6.1.5. Surface Modification with Silicon Compounds 6.1.6. Characterization 6.1.7. Uses 6.1.8. Industrial Hygiene and Safety 6.2. Electric‐Arc Process 6.3. Plasma Process 7. Precipitated Silicas 7.1. Introduction 7.2. Production 7.3. Properties 7.3.1. Physicochemical Properties 7.3.2. Surface Chemistry and Surface Modification 7.3.3. Chemical Composition and Analysis 7.4. Uses 7.5. Industrial Hygiene and Safety 8. Porosils 8.1. Introduction 8.2. Physical and Chemical Properties 8.2.1. Zeosils 8.2.2. Clathrasils 8.3. Manufacture of Porosils 8.3.1. Synthesis of Porosils 8.3.2. Dealumination of Aluminosilicate Zeolites 8.3.3. Formation of Melanophlogite 9. Toxicology 9.1. Experiences with Humans 9.2. Animal Experiments

In Situ Detection of Opal‐A in Jezero Crater, Mars

“…% for opal-C/CT. Therefore, opal-A generally contained a higher concentration of silanols, consistent with earlier reports (Day & Jones, 2008;Flörke et al, 2008;Segnit et al, 1965). We were not able to estimate silanol concentration in two opal-C/T samples, presumably because silanol concentrations were <0.1 wt.…”

In Situ Detection of Opal‐A in Jezero Crater, Mars

“…% for opal-C/CT. Therefore, opal-A generally contained a higher concentration of silanols, consistent with earlier reports (Day & Jones, 2008;Flörke et al, 2008;Segnit et al, 1965). We were not able to estimate silanol concentration in two opal-C/T samples, presumably because silanol concentrations were <0.1 wt.…”

Effect of silica morphology on the structure of hard-templated, non-precious metal catalysts for oxygen reduction

“…The distribution widths correlated strongly with pore size. Fumed silica particle distributions follow a similar correlation, widening with increasing particle size [21]. This similarity reflects the expected direct impact of silica particle size on catalyst pore size.…”

Influence of the Physicochemical and Microstructural Properties on the Insecticidal Efficacy of Diatomaceous Earth on the Poultry Pest Alphitobius diaperinus

“…Calcination is a thermal process that may lead to the loss of chemical groups related to MB adsorption, as suggested by different authors. − , Indeed, Yan and colleagues reported that calcined DE microspheres reached maximum MB adsorption capacity (when calcined at 600 °C) but became less efficient at adsorbing the dye as the calcination temperature increased. The authors linked the reduction in the adsorption capacity, among other factors, to the loss of hydroxyl groups during heating at higher temperatures.…”

In Situ Detection of Opal‐A in Jezero Crater, Mars

“…% for opal-C/CT. Therefore, opal-A generally contained a higher concentration of silanols, consistent with earlier reports (Day & Jones, 2008;Flörke et al, 2008;Segnit et al, 1965). We were not able to estimate silanol concentration in two opal-C/T samples, presumably because silanol concentrations were <0.1 wt.…”

Effect of silica morphology on the structure of hard-templated, non-precious metal catalysts for oxygen reduction

“…The distribution widths correlated strongly with pore size. Fumed silica particle distributions follow a similar correlation, widening with increasing particle size [21]. This similarity reflects the expected direct impact of silica particle size on catalyst pore size.…”

Influence of the Physicochemical and Microstructural Properties on the Insecticidal Efficacy of Diatomaceous Earth on the Poultry Pest Alphitobius diaperinus

“…Calcination is a thermal process that may lead to the loss of chemical groups related to MB adsorption, as suggested by different authors. − , Indeed, Yan and colleagues reported that calcined DE microspheres reached maximum MB adsorption capacity (when calcined at 600 °C) but became less efficient at adsorbing the dye as the calcination temperature increased. The authors linked the reduction in the adsorption capacity, among other factors, to the loss of hydroxyl groups during heating at higher temperatures.…”

In Situ Detection of Opal‐A in Jezero Crater, Mars

“…% for opal-C/CT. Therefore, opal-A generally contained a higher concentration of silanols, consistent with earlier reports (Day & Jones, 2008;Flörke et al, 2008;Segnit et al, 1965). We were not able to estimate silanol concentration in two opal-C/T samples, presumably because silanol concentrations were <0.1 wt.…”

Effect of silica morphology on the structure of hard-templated, non-precious metal catalysts for oxygen reduction

“…The distribution widths correlated strongly with pore size. Fumed silica particle distributions follow a similar correlation, widening with increasing particle size [21]. This similarity reflects the expected direct impact of silica particle size on catalyst pore size.…”

Influence of the Physicochemical and Microstructural Properties on the Insecticidal Efficacy of Diatomaceous Earth on the Poultry Pest Alphitobius diaperinus

“…Calcination is a thermal process that may lead to the loss of chemical groups related to MB adsorption, as suggested by different authors. − , Indeed, Yan and colleagues reported that calcined DE microspheres reached maximum MB adsorption capacity (when calcined at 600 °C) but became less efficient at adsorbing the dye as the calcination temperature increased. The authors linked the reduction in the adsorption capacity, among other factors, to the loss of hydroxyl groups during heating at higher temperatures.…”