SILICON

Name: Silicon (from the mineral Flint)

Symbol: Si

Group: 14

Period: 3

Block: p

Category: Metalloids

Atomic Number: 14

Atomic Mass: 28.085 u

Electrons per Shell: 2, 8, 4

Electronegativity: 2.04

Density: 1.9 g/cc

Melting Point: 1414ºC

Boiling Point: 2900ºC

Thermal Conductivity: 150 W (m·K)

Electrical Conductivity: 1000 S/m

Magnetic Order: Diamagnetic

Ordinary State: Solid

Oxidation States: -4, -3, -2, -1, 1, 2, 3, 4

Mohs Hardness: 6.5

Vickers Hardness: 9630

Brinell Hardness: No data

Most stable isotopes: Si-28 (92.2%), Si-29 (4.7%), Si-30 (3.1%)

Discoverer: Jöns Jakob Berzelius (1823)

Silicon (Si), a chemical element with an atomic number 14, is a Group 14 metalloid with a density of 2.33 g/cm³ and an abundance of 282,000 ppm (28.2%) in the Earth's crust, making it the second most abundant element after oxygen (O). Present in over 90% of terrestrial minerals, especially as silicates and oxides like quartz (SiO₂), silicon is a lithophile par excellence, with a strong affinity for oxygen. Its cosmic abundance (650 ppm in the observable universe) places it among the most common elements, formed in large quantities during stellar nucleosynthesis in massive stars through alpha-capture processes. The silicon nucleus, with 14 protons, is particularly stable, releasing significant energy during its formation, which makes it more abundant than nearby elements like magnesium (Mg) or sulfur (S), and only surpassed by iron (Fe) in rocky planets such as Mercury, Venus, Earth, and Mars.

Although pure silicon is not found in nature due to its reactivity with oxygen, its compounds, such as quartz and silicates, have been used since prehistory. The Stone Age (3.4 million years ago–2,000 BC) indirectly depended on silicon, as hominids used SiO₂-rich rocks, such as flint, to make tools, weapons, and rudimentary hammers. Gem-quality quartz, known as rock crystal, represented the purest form of silicon in antiquity, valued for its clarity and hardness (7 on the Mohs scale). Elemental silicon was first isolated in 1823 by the Swedish chemist Jöns Jacob Berzelius, who reduced silicon tetrafluoride (SiF₄) with potassium (K), naming it "silicium" (from Latin silex, flint) for its presence in siliceous rocks. This discovery marked a milestone in chemistry, although silicon did not gain prominence until the 20th century.

The modern importance of silicon lies in its role as a semiconductor in the electronics industry. Since the invention of the transistor in 1947, high-purity silicon (99.9999% or higher) has become the basis of microchips, solar cells, and integrated circuits, driving the technological revolution. Its global production (~8 million tons annually in 2025) reflects its demand in electronics, construction (glass, cement), and renewable energy. The history of silicon, from prehistoric tools to modern devices, underscores its role as the structural "bone" of Earth and its importance in contemporary science and technology.

Silicon (Si), a chemical element with atomic number 14, is a Group 14 metalloid with a density of 2.33 g/cm³ and an abundance of 282,000 ppm (28.2%) in the Earth's crust, making it the second most abundant element after oxygen (O). Its appearance is a dark bluish-gray with a metallic luster, but it is hard, brittle, and easily pulverized, with a hardness of ~7 on the Mohs scale, comparable to quartz (SiO₂). Although abundant in minerals like silicates and oxides, obtaining it in pure form is expensive (1–2 USD/kg for metallurgical silicon; ~100 USD/kg for high purity in 2025) due to the need for processing high-purity quartz sand through reduction with carbon and purification with chlorine (Siemens process) to achieve electronic grades (>99.9999%). Silicon is highly resistant to corrosion, especially in air and water, forming a protective layer of silicon dioxide (SiO₂) that stabilizes it.

Silicon exhibits several allotropic forms: monocrystalline, polycrystalline, and amorphous. Monocrystalline silicon, with an ordered structure, is essential in the electronics industry for semiconductors, such as microchips and solar cells, due to its conductivity controlled by doping (with boron, B, or phosphorus, P). Polycrystalline silicon is less ordered, used in less demanding applications, such as lower-cost solar panels. Amorphous silicon, with a disordered structure, has little industrial utility due to its lower stability and conductivity. From a metallurgical perspective, silicon is valued as an alloying agent, improving the mechanical and chemical properties of alloys, although its brittleness limits its use in its pure state.

In alloys, silicon is a key component in ferrosilicon (Fe-Si, 15–90% Si), used in steel production to improve strength, hardness, and elasticity, removing oxygen during smelting (deoxidizer). In aluminum silicates (Al-Si, ~5–12% Si), such as those used in automotive parts, silicon increases melt fluidity, reduces shrinkage, and improves wear and corrosion resistance. It also combines with magnesium (Mg) in Al-Si-Mg alloys for greater mechanical strength. In silicon bronzes (Cu-Si, ~1–4% Si), it provides corrosion resistance and self-lubrication, serving as an alternative to lead (Pb) bronzes in marine applications. Silicon's properties in alloys include greater rigidity, corrosion resistance, and thermal stability, although its high brittleness requires a balance with other metals to prevent fractures. Its melting point (1,414 °C) and chemical resistance make it ideal for corrosive environments, while its low thermal conductivity (150 W/(m·K)) and electrical conductivity (~10⁻⁴ S/m undoped) distinguish it from conductive metals.

The importance of silicon as an alloying agent lies in its ability to improve mechanical and chemical properties without adding toxicity, unlike lead or cadmium (Cd). Although its role as a semiconductor dominates the electronics industry (~8 million tons annually in 2025), its metallurgical applications are crucial in sectors such as construction, automotive, and machinery, where its abundance and chemical resistance compensate for purification costs.

Silicon, with atomic number 14, is a Group 14 metalloid, with a density of 2.33 g/cm³ and an abundance of approximately 282,000 ppm in the Earth's crust, making it the second most common element after oxygen. Its ability to form strong covalent bonds with non-metals makes it ideal for creating stable compounds, especially ceramics and intermetallics, which are notable for their corrosion resistance, hardness, and thermal stability. These compounds are essential in industries such as electronics, construction, and materials engineering, leveraging silicon's abundance and chemical versatility for high-performance applications.

With carbon, silicon forms silicon carbide, known as carborundum, an extremely hard ceramic material, with a hardness of 9 to 9.5 on the Mohs scale, comparable to diamond. This compound, with a melting point close to 2,730 °C, resists corrosion in acids, except hydrofluoric, and withstands high temperatures without degradation. Its covalent structure makes it ideal for abrasives, cutting tools, and high-power electronic components, such as diodes and transistors, thanks to its high thermal conductivity of approximately 490 W/(m·K) and its resistance to thermal shock. In industrial applications, its durability makes it a preferred material for extreme environments.

Nitrogen combines with silicon to form silicon nitride, a ceramic known for its exceptional toughness, with a fracture resistance of around 7 MPa·m¹/² and a decomposition point close to 1,900 °C. This compound resists acids, alkalis, and oxidation up to temperatures of 1,400 °C, making it suitable for bearings, turbines, and aerospace parts. Its low density, approximately 3.2 g/cm³, combined with its high mechanical strength, makes it a lightweight alternative to metals in advanced engineering applications where durability and weight are critical.

With oxygen, silicon forms silicon dioxide, commonly known as quartz in its pure form, or rock crystal in jewelry. This oxide, with a hardness of 7 on the Mohs scale and a melting point of approximately 1,710 °C, is extremely stable against corrosion by acids, except hydrofluoric, and alkalis. Its abundance in the Earth's crust, representing nearly 90% of minerals, makes it essential in the manufacture of glass, optical fibers, and electronic substrates. In construction, quartz and derived silicates are key components of cements and sands, while in jewelry, its clarity makes it valuable for decorative pieces.

Silicon also forms silicates, such as tungsten silicate, which are classified as intermetallic compounds due to their partial metallic character. This compound, with oxidation resistance up to approximately 1,550 °C, is used in coatings and heating elements, although its stability varies depending on composition and environmental conditions. Other silicates, such as alkali metal silicates, are less stable and more reactive, limiting their applications. Global silicon production, reaching about 8 million tons annually in 2025, reflects the importance of these compounds in modern technologies, from high-performance ceramics to electronics, where their corrosion resistance and structural robustness are irreplaceable.

Silicon (Si), a chemical element with atomic number 14, is a Group 14 metalloid with a density of 2.33 g/cm³ and an abundance of approximately 282,000 ppm (28.2%) in the Earth's crust. Its chemical versatility allows it to interact with base metals, such as aluminum (Al), iron (Fe), nickel (Ni), and copper (Cu), forming alloys or intermetallic compounds that improve mechanical and chemical properties. However, its compatibility with p-block metals, such as lead (Pb) or bismuth (Bi), is limited due to lower solubility, which restricts its use in these combinations. In metallurgy, silicon is primarily used as an alloying agent in small quantities to optimize specific characteristics of alloys, leveraging its abundance and chemical stability.

Silicon is soluble in base metals during smelting, integrating through chemical contact fusion. In alloys with aluminum, such as aluminum silicates (Al-Si, typically 5–12% Si), silicon improves melt fluidity, reduces shrinkage during solidification, and increases wear and corrosion resistance, being common in automotive parts, such as engine blocks. With iron, it forms ferrosilicon (Fe-Si, 15–90% Si), an essential component in steel production, where it acts as a deoxidizer by removing dissolved oxygen, preventing defects in the molten metal. It also increases the strength and elasticity of steel. In nickel alloys (Ni-Si), silicon improves corrosion resistance in high-temperature environments, used in turbines and aerospace components. With copper, it is incorporated into bronzes (Cu-Si, 1–4% Si) and brasses, where it acts as a hardener, improving mechanical and corrosion resistance, especially in marine applications.

The addition of silicon is done in low doses, generally between 0.5% and 2%, as higher concentrations embrittle alloys, reducing their ductility and increasing the risk of fracture. Its three main functions as an alloying agent are: to act as a deoxidizer, removing oxygen to improve metal quality; to serve as an anticorrosive agent, forming stable protective layers in the presence of water or acids; and to increase electrical conductivity in steels, especially in silicon steels (up to 3% Si) used in transformers and electric motors, where it reduces magnetic losses. In bronzes and brasses, silicon also provides self-lubricating properties, similar to lead, but without toxicity.

With p-block metals, such as lead, bismuth, or tin (Sn), silicon's solubility is low, limiting the formation of homogeneous alloys. However, it can form intermetallic compounds, such as aluminum silicate (Al₂SiO₅) or magnesium silicide (Mg₂Si), which improve mechanical strength in specific alloys. Global silicon production (8 million tons in 2025) reflects its importance in metallurgy, especially in steel and aluminum production, where its properties as an alloying agent compensate for purification costs (1–2 USD/kg for metallurgical grade). Silicon's ability to improve the durability, strength, and conductivity of alloys makes it indispensable in modern industry, despite limitations in its compatibility with p-block metals.

Silicon, with atomic number 14, is a Group 14 metalloid, with a density of 2.33 g/cm³ and an abundance of approximately 282,000 ppm in the Earth's crust, making it the second most abundant element after oxygen. Although its elemental form is crucial in the electronics industry as a semiconductor, approximately 90% of the world's silicon production, reaching about 8 million tons annually in 2025, is used in the form of oxide (SiO₂) as a raw material in construction, furnace and crucible manufacturing, and glass production. Its corrosion resistance, deoxidizing capability, and alloying properties make it indispensable in metallurgy, electronics, and other industries, despite purification costs (~1–2 USD/kg for metallurgical grade; ~100 USD/kg for high purity).

In construction, silicon dioxide, present in sands and quartz, is the basis of materials like cement, bricks, and porcelains, which leverage its chemical stability and hardness (7 Mohs). In glass manufacturing, silicon forms the main structure of common (soda-lime) and specialized glasses, such as borosilicate, while in furnaces and crucibles, its heat resistance (1,710 °C melting point of SiO₂) ensures durability in extreme environments. In electronics, pure forms of quartz are used to produce optical fiber, which surpasses copper (Cu) and silver (Ag) in data transmission due to its low signal loss and high bandwidth capacity. Fiberglass, reinforced with silicon, is used in composites for construction, automotive, and aerospace, offering mechanical and thermal resistance.

In metallurgy, silicon acts as a key deoxidizer during the smelting of base metals, such as copper, steel, stainless steel, nickel (Ni), and cobalt (Co). By "stealing" dissolved oxygen, it forms stable oxides (SiO₂), reducing grain size and increasing the toughness of the alloy. In carbon steel, the addition of silicon up to 1.1%, combined with manganese (Mn), improves flexibility and impact resistance, making it ideal for tools like pneumatic hammers, high-carbon hammers, demolition parts, and excavator blades. It is also used in springs, where its elasticity withstands prolonged mechanical stress. In steels for electrical parts, such as those in transformers and motors, silicon (up to ~6%) increases electrical conductivity and reduces magnetic losses, although it does not improve corrosion resistance, unlike ferrosilicon (Fe-Si, 15–90% Si), which is specific for steel production.

In copper alloys, silicon, up to 2%, forms silicon bronzes (Cu-Si), which increase toughness and corrosion resistance, though they reduce electrical conductivity. These bronzes, easier to mold than traditional (Cu-Sn) ones, are affordable and used in marine and structural applications, but concentrations above 2% make them brittle. In austenitic stainless steels, such as AISI 304 and 316, silicon (1%) acts more as a deoxidizer than as an anticorrosive agent, as higher levels compromise toughness. The Hastelloy D alloy, with a minimum of 8% silicon, is an exception, as it resists sulfuric acid (H₂SO₄) at any concentration and temperature, even boiling, but its chemical complexity and high cost (50–100 USD/kg) limit its use.

As an anticorrosive agent, silicon is exceptional due to its ability to form a passivating SiO₂ layer, which protects it against all common oxidizing and reducing acids, except hydrofluoric acid (HF), which attacks it catastrophically, forming silicon tetrafluoride (SiF₄). Even sulfuric acid, dilute or concentrated, does not affect silicon, neither at room temperature nor when hot, making it ideal for corrosive environments. In aluminum bronzes (Al 7.5%, Si 2.5%, with traces of Ni, Zn, and a Cu base), the combination of passivating layers of aluminum oxide (Al₂O₃) and SiO₂ maximizes resistance to sulfate formation, common in copper alloys, providing a durable gold-like luster, ideal for costume jewelry and ornamental pieces. However, these alloys, produced in specialized furnaces, are difficult to work manually, limiting their use in artisanal jewelry. Silicon's versatility in these applications, combined with its abundance and chemical resistance, ensures its relevance in modern industry, despite purification challenges.