Properties and Overview of Silicon

Overview:

Silicon (Si) is a chemical element with the symbol Si and atomic number 14, belonging to group 14 of the periodic table. It is classified as a metalloid, which means it possesses properties of both metals and nonmetals. Silicon is the second most abundant element in the Earth's crust, making up about 27.7% of its mass. This high abundance is primarily due to silicon's presence in various forms of silicon dioxide (silica) and silicate minerals. Silicon was first identified in 1787 by Antoine Lavoisier and later isolated in its pure form by Jöns Jacob Berzelius in 1824. Physically, silicon is a hard, brittle crystalline solid with a bluish-gray metallic luster. It has a density of about 2.33g/cm³, a melting point of 1,414°C, and a boiling point of 3,265°C. These high melting and boiling points reflect the strong covalent bonds in its crystal lattice. Silicon crystallizes in a diamond cubic structure, contributing to its semiconducting properties and making it an essential material in the electronics industry. In its crystalline form, silicon is a relatively good conductor of heat, with a thermal conductivity of 149 W/m·K at room temperature. However, it behaves as a semiconductor in terms of electrical conductivity, which can be manipulated by adding impurities, a process known as doping.
Chemically, silicon is relatively inert at room temperature but becomes more reactive at higher temperatures. It readily forms compounds with oxygen, resulting in the formation of silicon dioxide (SiO₂), commonly known as silica, which exists in various forms, such as quartz, sand, and glass. Silicon also forms silicates, the building blocks of most minerals in the Earth's crust. In its pure form, silicon reacts with halogens such as fluorine and chlorine, forming silicon tetrahalides (SiX₄), and with hydrogen to form silanes (SiH₄). Silicon does not react with most acids but dissolves in hydrofluoric acid, forming hexafluorosilicic acid (H₂SiF₆). Due to its strong affinity for oxygen, silicon is crucial in ceramics, glass, and refractories.
Regarding safety, silicon in its elemental form is not considered hazardous to human health. It is chemically inert and poses no significant risk when appropriately handled. However, inhalation of crystalline silica dust, which is a common form of silicon dioxide, can lead to serious respiratory diseases such as silicosis, lung cancer, and chronic obstructive pulmonary disease (COPD). These risks are particularly relevant in occupational settings where workers are exposed to airborne silica particles, such as mining, construction, and glass manufacturing. Safety measures, including personal protective equipment (PPE) such as masks and respirators, and engineering controls like ventilation and dust suppression systems, are critical to prevent inhalation and reduce exposure to silica dust.

Production:

Silicon is produced commercially through several processes, the most common of which is the reduction of silicon dioxide using carbon in an electric arc furnace. This method produces metallurgical-grade silicon, which is about 98-99% pure. To obtain higher-purity silicon for semiconductor applications, further refinement is necessary. This is typically achieved through the Siemens process, which involves converting metallurgical-grade silicon to a volatile silicon compound like trichlorosilane (SiHCl₃) and then purifying it by fractional distillation. The purified compound is then decomposed to pure silicon through chemical vapor deposition at high temperatures, resulting in electronic-grade silicon with a purity of 99.9999999% or higher. Another method for producing high-purity silicon is the Czochralski process, where a single silicon crystal is grown from molten silicon. This single-crystal silicon, a boule, is then sliced into thin wafers for use in semiconductor devices.

Applications:

Silicon's applications are vast and diverse, owing to its unique properties. One of its most critical applications is in the electronics industry, where it serves as the primary material for semiconductors used in integrated circuits and microchips. Silicon's semiconducting properties and its ability to form an insulating layer of silicon dioxide when oxidized make it ideal for use in transistors, diodes, solar cells, and other electronic components. Silicon wafers are the foundation of most modern electronic devices, from computers and smartphones to advanced medical equipment and renewable energy technologies.
In addition to its role in electronics, silicon is widely used in producing glass, ceramics, and cement. Silica, a silicon dioxide form, is the primary ingredient in most commercial glasses, contributing to their durability and resistance to thermal shock. In ceramics, silicon carbide (SiC) is a crucial material known for its hardness, thermal stability, and resistance to chemical corrosion, making it suitable for high-temperature applications, such as kiln linings, abrasives, and cutting tools. In construction, silicon-based materials, such as silicate minerals and silica fume, are used in concrete production to improve strength and durability.
Silicon is also important in metallurgy as an alloying agent. It improves the strength, hardness, and corrosion resistance of aluminum, steel, and other metals. Silicon alloys, such as ferrosilicon and aluminum-silicon, are essential in the production of cast irons. In this process, silicon serves as a deoxidizer, removing oxygen from the molten metal and preventing oxidation. In addition, silicon alloys are used in the automotive and aerospace industries, where materials must withstand high temperatures and mechanical stresses.
In renewable energy, silicon is a crucial material in photovoltaic (solar) cells, which convert sunlight into electricity. The photovoltaic industry primarily relies on crystalline silicon used to manufacture solar panels. Silicon-based solar cells are currently the most widely used and commercially available, accounting for most of the global solar market. Recent advancements in silicon technology, such as the development of monocrystalline and polycrystalline silicon cells, have increased the efficiency and cost-effectiveness of solar energy systems.

Summary:

Silicon is a versatile and abundant element with many physical and chemical properties that make it invaluable across multiple industries, including electronics, construction, metallurgy, and renewable energy. Its semiconducting properties are fundamental to the electronics industry, where silicon is the cornerstone of modern microelectronics. While silicon is generally safe in its elemental form, precautions are necessary to avoid inhaling silica dust, which poses significant health risks. Silicon is produced on a large scale by reducing silicon dioxide, and advanced refinement processes are employed to achieve the high purity levels required for electronic applications. As technology advances, silicon's role in emerging fields such as renewable energy and advanced materials will likely expand further, underscoring its importance in current and future technological developments.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for silicon below: