# silica gel > granular, vitreous, porous form of silicon dioxide **Wikidata**: [Q308976](https://www.wikidata.org/wiki/Q308976) **Wikipedia**: [English](https://en.wikipedia.org/wiki/Silica_gel) **Source**: https://4ort.xyz/entity/silica-gel ## Summary Silica gel is a granular, vitreous, porous form of synthetic amorphous silicon dioxide that functions as a solid, cross‑linked gel. It is widely used as a hygroscopic desiccant, absorbent, and column‑packing material in chromatography and other industrial processes. ## Key Facts - **Chemical nature:** Granular, porous silica (SiO₂) classified as a synthetic amorphous silica gel.【source】 - **Density:** 2.20 g · cm⁻³ (measured at 20 °C).【source】 - **Melting point:** 3 110 °F; **Boiling point:** 4 046 °F at 760 mm Hg.【source】 - **Vapor pressure:** 0 mm Hg (practically non‑volatile).【source】 - **CAS Registry Numbers:** 68855‑54‑9 (silica gel) and 112926‑00‑8 (silicon dioxide).【source】 - **Hazard limits (NIOSH):** Time‑Weighted Average exposure limit = 6 mg · m⁻³; Immediately Dangerous to Life or Health (IDLH) = 3 000 mg · m⁻³.【source】 - **Primary classifications:** Subclass of gel, column‑packing material, and absorbent; instance of chemical substance.【source】 - **Key identifiers:** KEGG D06521; EC 272‑489‑0; NIOSH Pocket Guide ID 0552; UMLS C0074530.【source】 - **Common aliases:** Silica gel, Silicagel, Gel de silice, Trockensalz, 63231‑67‑4.【source】 - **Modified forms for chromatography:** C18, C8, Cyano, Amino, and Phenyl silica gels.【source】 ## FAQs ### Q: What is silica gel used for? A: Silica gel is primarily used as a hygroscopic desiccant to absorb moisture, as an absorbent for gases and liquids, and as a column‑packing material in chromatography. ### Q: Is silica gel hazardous? A: While silica gel itself is chemically inert, exposure to fine particles can be hazardous; NIOSH sets a TWA limit of 6 mg · m⁻³ and an IDLH limit of 3 000 mg · m⁻³. ### Q: What is silica gel made of? A: It is a porous, amorphous form of silicon dioxide (SiO₂) produced synthetically as a cross‑linked gel. ### Q: Can silica gel be regenerated after it absorbs moisture? A: Yes—heated drying restores its adsorption capacity, though the source material does not detail specific regeneration procedures. ### Q: How does silica gel differ from regular sand? A: Unlike sand, silica gel has a highly porous, high‑surface‑area structure and is hygroscopic, allowing it to adsorb water vapor efficiently. ## Why It Matters Silica gel’s unique porous structure gives it an exceptionally high surface area, making it one of the most effective solid desiccants available. By adsorbing moisture from sealed containers, it protects pharmaceuticals, electronics, food, and other moisture‑sensitive products from degradation, extending shelf life and preserving functionality. In analytical chemistry, modified silica gels (e.g., C18, Cyano) serve as the stationary phase in high‑performance liquid chromatography, enabling precise separation of complex mixtures. Its chemical inertness, low vapor pressure, and high thermal stability (melting point > 3 000 °F) allow safe handling across a wide temperature range. However, fine silica particles can pose inhalation hazards, prompting regulatory exposure limits and safety guidelines. Consequently, silica gel is a critical material in both industrial preservation and scientific analysis, balancing utility with well‑defined health safeguards. ## Notable For - **Extremely low vapor pressure (0 mm Hg)**, making it non‑volatile under normal conditions. - **High thermal stability**: melts at 3 110 °F and boils at 4 046 °F. - **Hygroscopic capability**: widely used as a desiccant to protect moisture‑sensitive goods. - **Versatility in chromatography**: base for C18, C8, Cyano, Amino, and Phenyl modified gels. - **Regulated occupational exposure** with specific NIOSH limits (TWA 6 mg · m⁻³, IDLH 3 000 mg · m⁻³). ## Body ### Composition and Structure - Silica gel is a synthetic amorphous form of silicon dioxide (SiO₂). - It consists of a cross‑linked network of Si–O bonds, creating a granular, vitreous, and highly porous matrix. ### Physical Properties - **Density:** 2.20 g · cm⁻³ (20 °C). - **Melting point:** 3 110 °F; **Boiling point:** 4 046 °F at standard pressure. - **Vapor pressure:** 0 mm Hg, indicating negligible volatility. - **Molecular mass:** Reported as 60.1 Da (source: CDC NIOSH). ### Classification and Related Materials - Subclass of **gel**, **column‑packing material**, and **absorbent**. - Part of the broader class **synthetic amorphous silica**. - Related modified gels used in chromatography: **C18, C8, Cyano, Amino, Phenyl** silica gels. ### Applications - **Desiccant:** Adsorbs moisture from sealed environments, protecting electronics, pharmaceuticals, and food. - **Absorbent:** Captures gases and liquids in industrial processes. - **Chromatography:** Serves as the stationary phase for separating chemical mixtures; functionalized variants tailor selectivity. ### Safety and Exposure Limits - **NIOSH TWA:** 6 mg · m⁻³ (average 8‑hour exposure). - **IDLH:** 3 000 mg · m⁻³ (immediate danger to life or health). - Classified as a **hygroscopic agent** and associated with **silica gel exposure** hazards. ### Identifiers and References - **CAS:** 68855‑54‑9 (silica gel), 112926‑00‑8 (silicon dioxide). - **KEGG:** D06521. - **EC number:** 272‑489‑0 (also 601‑214‑2). - **NIOSH Pocket Guide ID:** 0552. - **UMLS CUI:** C0074530. - **ECHA infocard:** 100.065.880 (68855‑54‑9) and 100.128.559 (112926‑00‑8). ### Visual Resources - Images: ![Silica gel indicator](https://commons.wikimedia.org/wiki/Special:FilePath/Indicating-silica-gel.png) and schematic surface view. --- All statements are derived exclusively from the supplied source material. ## References 1. [ChemIDplus](https://chem.nlm.nih.gov/chemidplus/rn/68855-54-9) 2. Silicon dioxide. ECHA Substance Infocard database 3. Freebase Data Dumps. 2013 4. [Source](http://www.cdc.gov/niosh/npg/npgd0552.html) 5. Kieselguhr, soda ash flux-calcined. ECHA Substance Infocard database 6. Medical Subject Headings 7. UMLS 2023 8. Quora 9. KBpedia 10. [OpenAlex](https://docs.openalex.org/download-snapshot/snapshot-data-format)