Applications of Silicon

Compounds

Most silicon is used industrially without purification and, in fact, is usually relatively little processed from its native form.More than 90 percent of the Earth's crust is made up of silicate minerals, which are compounds of silicon and oxygen that often carry metal ions while negatively charged silicate anions require cations to balance the charge.Many of these have immediate commercial use, such as clay, silica sand, and most building stones.Therefore, the vast majority of uses of silicon are as structural compounds, as silicate minerals or silicon dioxide (coarse silicon dioxide).Silicates are used in the manufacture of Portland cement (mainly calcium silicate) used in building mortars and modern stuccoes, but more importantly, with silica sand and gravel (often containing silicate minerals such as granite) Combined, concrete is the basis for most of the largest industrial construction projects in the modern world.

Silica is used to make refractory bricks, a type of ceramic.Silicate minerals are also found in white ceramics, an important class of products that often contain various types of fired clay minerals (natural phyllosilicates).One example is porcelain, which is based on the silicate mineral kaolinite.Traditional glass (silicon-based soda-lime glass) performs many of the same functions and is also used in windows and containers.In addition, specialty silica-based glass fibers are used in optical fibers, as well as in the production of glass fibers for structural support and glass wool for thermal insulation.

Silicones are commonly used in waterproofing treatments, molding compounds, mold release agents, mechanical seals, high temperature greases and waxes, and caulking compounds.Silicones are also sometimes used in breast implants, contact lenses, explosives and fireworks.Silly putty was originally made by adding boric acid to silicone oil.Other silicon compounds are used as high-tech abrasives and new high-strength ceramics based on silicon carbide. Silicon is a component of some superalloys.

Alloys 

Elemental silicon is added to molten cast iron in the form of ferrosilicon or calcium-silicon alloys to improve the properties of cast thin sections and to prevent cementite from forming when exposed to outside air.The presence of the element silicon in the molten iron acts to absorb oxygen and thus allows tighter control of the steel's carbon content, which must be kept within narrow limits for each type of steel.The production and use of ferrosilicon is an indicator of the steel industry, and although this form of elemental silicon is very impure, it accounts for 80% of the world's free silicon use.Silicon is an important component of electrical steels, changing their electrical resistivity and ferromagnetic properties.

The properties of silicon can be used to modify alloys with metals other than iron. "Metallurgical grade" silicon is silicon that is 95-99% pure. About 55% of the world's metallurgical pure silicon consumption is used in the production of aluminum-silicon alloys (silicon-aluminum alloys) for aluminum castings, mainly in the automotive industry.The importance of silicon in aluminum castings is that the significant amount (12%) of silicon in aluminum forms a eutectic mixture that solidifies with little heat shrinkage.This greatly reduces tearing and cracking due to stress as the cast alloy cools to solidify. Silicon also significantly increases the hardness of aluminum, which increases wear resistance.

Electronics

Most of the elemental silicon produced is still ferrosilicon, with only about 20% being refined to metallurgical grade purity (a total of 1.3-1.5 million metric tons/year). An estimated 15% of the world's metallurgical-grade silicon production is further refined to semiconductor purity.This is usually "ninety-nine" or 99.9999999% pure,[98] single crystal material with few defects.Single crystal silicon of this purity is typically produced by pulling methods and is used to produce silicon wafers used in the semiconductor industry, electronics and some high-cost, high-efficiency photovoltaic applications.Pure silicon is an intrinsic semiconductor, which means that, unlike metals, it conducts electron holes and electrons released from atoms by heat; the electrical conductivity of silicon increases with temperature.Pure silicon has too low electrical conductivity (i.e., too high resistivity) to be used as a circuit element in electronics. In practice, pure silicon is doped with low concentrations of certain other elements, which greatly increases its conductivity and tunes its electrical response by controlling the number and charge (positive or negative) of activated carriers.Such control is necessary for transistors, solar cells, semiconductor detectors, and other semiconductor devices used in the computer industry and other technical applications.In silicon photonics, silicon can be used as a continuous wave Raman laser medium to generate coherent light.

In common integrated circuits, a single-crystal silicon wafer serves as the mechanical support for the circuits, which are formed by doping and insulated from each other by a thin layer of silicon oxide, a silicon oxide that is easily produced on the surface of silicon by a thermal oxidation process. Insulator or localized oxidation (LOCOS), which involves exposing elements to oxygen under appropriate conditions that can be predicted by the Deal–Grove model.Silicon has become the most popular material for high-power semiconductors and integrated circuits because it can withstand the highest temperatures and the greatest electrical activity without suffering avalanche breakdown (an electron avalanche when heat creates free electrons and holes, which This in turn passes more current, generating more heat). Also, the insulating oxide of silicon is insoluble in water, which makes it superior to germanium (an element with similar properties that is also used in semiconductor devices) in some manufacturing techniques.

Single-crystal silicon is expensive to produce and is usually only justified in the production of integrated circuits, where tiny crystal defects interfere with tiny circuit paths.For other uses, other types of pure silicon can be used.These include hydrogenated amorphous silicon and upgraded metallurgical grade silicon (UMG-Si), used to produce low-cost, large-area electronics and large-area, low-cost thin-film solar cells in applications such as liquid crystal displays.This semiconductor grade of silicon, which is either slightly less pure or polycrystalline rather than monocrystalline, is produced in comparable quantities to monocrystalline silicon: 75,000 to 150,000 metric tons per year.The market for secondary silicon is growing faster than monocrystalline silicon. Production of polysilicon, primarily used in solar cells, is expected to reach 200,000 metric tons per year by 2013, while monocrystalline semiconductor-grade silicon is expected to remain below 50,000 tons per year.

Quantum dots

Silicon quantum dots are produced by heat-treating hydrogen silsesquioxane into nanocrystals of a few nanometers to a few micrometers, showing size-dependent luminescence properties.Nanocrystals display large Stokes shifts, converting photons in the ultraviolet range to photons in the visible or infrared, depending on particle size, allowing applications in quantum dot displays and Glowing solar concentrator.One benefit of using silicon-based quantum dots compared to cadmium or indium is the non-toxic, metal-free nature of silicon.Another application of silicon quantum dots is the detection of hazardous substances. Sensor exploits quantum dots' luminescent properties by quenching photoluminescence in the presence of harmful substances.There are many approaches for hazardous chemical sensing, some of which are electron transfer, fluorescence resonance energy transfer, and photocurrent generation.When the energy of the lowest unoccupied molecular orbital (LUMO) is slightly lower than the conduction band of the quantum dot, electron transfer quenching occurs, allowing the transfer of electrons between the two, thereby preventing the hole and electronic composite.The effect can also be reversed, with the highest occupied molecular orbital (HOMO) of the donor molecule slightly above the valence band edge of the quantum dot, allowing electrons to transfer between them, filling holes and preventing recombination.Fluorescence resonance energy transfer occurs when a complex is formed between the quantum dot and the quencher molecule.The complex will continue to absorb light, but when the energy is switched to the ground state, it will not release a photon, quenching the material.The third approach uses a different approach, by measuring the photocurrent emitted by the quantum dots rather than monitoring a photoluminescent display.If the concentration of the desired chemical is increased, the photocurrent emitted by the nanocrystal changes in response.