Silicon Dioxide

Silicon dioxide (SiO₂) is an inorganic compound widely found in nature. It is the main component of sand, quartz, and crystal minerals. Composed of silicon atoms and oxygen atoms bonded together by covalent bonds, silicon dioxide has a relatively simple and stable chemical structure. In its pure form, it appears as a white powder or a colorless, transparent crystalline substance. However, silicon dioxide in nature often exhibits various colors, such as yellow, brown, and black, due to the presence of impurities.

Form and Appearance

Silicon dioxide exists in multiple forms. Amorphous silicon dioxide, such as that found in diatomite, is typically a white or light yellow powder with a loose texture. Crystalline silicon dioxide, like quartz crystals, has a regular hexagonal columnar shape, is colorless and transparent, and possesses a glassy luster.

Hardness and Density

Crystalline silicon dioxide has a high hardness, with a Mohs hardness of around 7, allowing it to leave scratches on many common materials. Its density varies depending on the crystalline form, ranging from 2.2 to 2.65 grams per cubic centimeter.

Solubility and Melting Point

Silicon dioxide is almost insoluble in water and common organic solvents, and it is highly chemically stable. It has a high melting point, typically around 1600°C to 1700°C, which enables it to maintain structural stability even at high temperatures.

Optical Properties

Crystalline silicon dioxide has excellent light transmittance, especially in the visible light range, which is one of the reasons it is used in the manufacture of optical instruments. It also has certain refractive and reflective properties, making it suitable for the design and processing of optical lenses.

Stability

Silicon dioxide is extremely chemically stable. At room temperature and pressure, it does not readily react with most common chemicals such as acids except hydrofluoric acid), bases, and salts. However, it reacts with hydrofluoric acid to produce silicon tetrafluoride gas and water. This unique chemical reactivity is utilized in specific industrial processes.

Oxidation and Reduction Characteristics

Silicon in SiO2 is in its highest oxidation state (+4). It is generally very difficult to oxidize further and typically exists as a stable oxide. Only under extreme reducing conditions can it be reduced to elemental silicon or other forms.

Adsorption

Amorphous silicon dioxide has a large specific surface area and porous structure, which gives it good adsorption properties. It can absorb impurities, small molecules, and gases or liquids. For example, diatomite (whose main component is silicon dioxide) is commonly used as an adsorbent for wastewater treatment and air purification.

Electrical Insulation

Silicon dioxide is an excellent electrical insulator. It is widely used in electronic component packaging and as an insulating material for electrical wires and cables. Its insulating properties effectively prevent electrical leakage and ensure the safe operation of electrical equipment.

Silicon dioxide is relatively safe under normal conditions. However, inhaling large amounts of it, especially crystalline dust, can lead to silicosis and other lung diseases. Therefore, strict protective measures are necessary for production and processing operations that generate silicon dioxide dust. If it is not exposed to extremely corrosive environments or subjected to physical damage, silicon dioxide can maintain its stable physical and chemical properties over the long term.