Silicon dioxide
[CAS# 7631-86-9]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Oxides and peroxides >> Non-metal oxides and peroxides
• Name: Silicon dioxide
• Synonyms: Silica
• Molecular Formula: SiO₂
• Molecular Weight: 60.08
• CAS Registry Number: 7631-86-9
• EC Number: 231-545-4
• SMILES: O=[Si]=O

Properties

• Density: 1.10-1.20 g/cm³ (Expl.), 2.2 - 2.6 g/mL (Expl.)
• Melting point: 1709.4 - 1710.6 ºC (Expl.)
• Boiling point: 2229.4 - 2230.6 ºC (Expl.)
• Solubility: Insoluble (water, acid), soluble (HF) (Expl.)

Safety Data

• Hazard Symbols: Pictogram(s)
• Risk Codes: R36/37
• Safety Description: S26;S37/39

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	2	H371
Specific target organ toxicity - single exposure	STOT SE	1	H370
Skin corrosion	Skin Corr.	1C	H314
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Acute toxicity	Acute Tox.	4	H312
Germ cell mutagenicity	Muta.	1B	H340
Carcinogenicity	Carc.	1A	H350
Specific target organ toxicity - repeated exposure	STOT RE	1	H373
Specific target organ toxicity - single exposure	STOT SE	2	H335
Substances or mixtures which in contact with water emit flammable gases	Water-react.	1	H260
Substances or mixtures which in contact with water emit flammable gases	Water-react.	3	H261
Flammable liquids	Flam. Liq.	2	H225
Carcinogenicity	Carc.	1B	H350
Skin corrosion	Skin Corr.	1	H314
Aspiration hazard	Asp. Tox.	1	H304
Skin sensitization	Skin Sens.	1	H317

Discovory and Applicatios

Silicon dioxide, also known as silica, is a naturally occurring compound composed of silicon and oxygen with the chemical formula SiO₂. It is one of the most abundant minerals in the Earth's crust and exists in various forms, both crystalline and amorphous. Crystalline forms include quartz, cristobalite, and tridymite, while amorphous silica occurs in materials such as opal and synthetic silica gels.

The discovery and early recognition of silicon dioxide dates back to ancient times. Quartz crystals were known to early civilizations, valued for their clarity and hardness. Although the compound itself was not chemically understood until much later, its physical manifestations were widely utilized. The modern scientific identification of silicon dioxide and its composition was established in the 19th century with the development of analytical chemistry techniques.

Silicon dioxide plays a fundamental role in numerous industries due to its unique combination of physical and chemical properties. It is chemically inert under most conditions, has a high melting point (approximately 1,710 °C), and possesses excellent mechanical strength and thermal stability. These features have made it an essential material in a wide array of applications.

One of the most widespread uses of silicon dioxide is in the production of glass. When silica is heated with sodium carbonate and calcium oxide, it forms soda-lime glass, the most common type of glass used in windows, bottles, and containers. High-purity fused silica is used to produce optical glass and laboratory glassware due to its high transparency and resistance to thermal shock.

In the electronics industry, silicon dioxide is a critical material in the manufacture of semiconductors. It is used as an insulating layer and as a mask during the photolithography process in integrated circuit fabrication. Silicon wafers, the base material for most electronic devices, are often coated with a thin layer of silicon dioxide to protect and insulate components.

Silicon dioxide also has numerous applications in construction. It is a major component of sand, which is used to make concrete, mortar, and bricks. In cement production, silica acts as a binder and helps improve the strength and durability of the material.

In the food industry, amorphous silicon dioxide is used as an anti-caking agent in powdered foods and supplements. It prevents clumping and improves the flow of materials during processing and packaging. It is generally recognized as safe for consumption in small quantities.

In the pharmaceutical industry, silicon dioxide serves multiple functions, including as a glidant to enhance powder flow in tablet manufacturing, as a carrier for active ingredients, and as a desiccant in packaging to protect moisture-sensitive products.

Synthetic amorphous silica is also widely used in cosmetics and personal care products as a thickening agent, abrasive, or absorbent. It contributes to the texture and performance of formulations in products such as toothpaste, powders, and skin creams.

In environmental and filtration technologies, silicon dioxide is employed in the form of silica gel, a highly porous material capable of adsorbing moisture and other substances. Silica gel is commonly used as a desiccant in packaging to protect against humidity. In chromatography, silica gel serves as a stationary phase for separating mixtures based on molecular properties.

Silicon dioxide’s role in biotechnology and life sciences has expanded with the development of silica-based materials for drug delivery, DNA purification, and biosensors. Functionalized silica surfaces can selectively bind biological molecules, facilitating advanced diagnostic and therapeutic techniques.

Despite its many beneficial uses, crystalline silica poses health risks when inhaled in fine particulate form over long periods. Occupational exposure, especially in mining, construction, and ceramics industries, can lead to respiratory conditions such as silicosis. Safety guidelines and protective measures are implemented in workplaces to mitigate such risks.

Silicon dioxide remains a cornerstone of modern material science, owing to its availability, versatility, and stability. Its ongoing utilization in both traditional and cutting-edge technologies highlights its enduring importance in scientific and industrial development.

References

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2025 Self-propelling intelligent nanomotor: A dual-action photothermal and starvation strategy for targeted deep tumor destruction. Biomaterials, 312.
DOI: 10.1016/j.biomaterials.2024.122968