Silicon is achemical element; it hassymbolSi andatomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is atetravalentnon-metal (sometimes considered as ametalloid) andsemiconductor. It is a member ofgroup 14 in the periodic table:carbon is above it; andgermanium,tin,lead, andflerovium are below it. It is relatively unreactive. Silicon is a significant element that is essential for several physiological and metabolic processes in plants. Silicon is widely regarded as the predominant semiconductor material due to its versatile applications in various electrical devices such as transistors, solar cells, integrated circuits, and others. These may be due to its significantband gap, expansive optical transmission range, extensive absorption spectrum, surface roughening, and effective anti-reflection coating.[14]
Because of its high chemical affinity for oxygen, it was not until 1823 thatJöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Itsoxides form a family ofanions known assilicates. Its melting and boiling points of 1414 °C and 3265 °C, respectively, are the second highest among all the metalloids and nonmetals, being surpassed only byboron.[a]
Most silicon is used commercially without being separated, often with very little processing of the natural minerals. Such use includes industrial construction withclays,silica sand, andstone. Silicates are used inPortland cement formortar andstucco, and mixed with silica sand andgravel to makeconcrete for walkways, foundations, and roads. They are also used in whitewareceramics such asporcelain, and in traditionalsilicate-basedsoda–lime glass and many other specialtyglasses. Silicon compounds such assilicon carbide are used as abrasives and components of high-strength ceramics. Silicon is the basis of the widely used synthetic polymers calledsilicones.
The late 20th century to early 21st century has been described as the Silicon Age (also known as theDigital Age orInformation Age) because of the large impact that elemental silicon has on the modern world economy. The small portion of very highly purified elemental silicon used insemiconductor electronics (<15%) is essential to thetransistors andintegrated circuit chips used in most modern technology such assmartphones and othercomputers. In 2019, 32.4% of the semiconductor market segment was for networks and communications devices, and the semiconductors industry is projected to reach $726.73 billion by 2027.[15]
Silicon is an essential element in biology. Only traces are required by most animals, but somesea sponges and microorganisms, such asdiatoms andradiolaria, secrete skeletal structures made of silica. Silica is deposited in many plant tissues.[16]
In 1787,Antoine Lavoisier suspected thatsilica might be an oxide of a fundamentalchemical element,[18] but thechemical affinity of silicon for oxygen is high enough that he had no means to reduce the oxide and isolate the element.[19] After an attempt to isolate silicon in 1808,Sir Humphry Davy proposed the name "silicium" for silicon, from the Latinsilex,silicis for flint, and adding the "-ium" ending because he believed it to be a metal.[20] Most other languages use transliterated forms of Davy's name, sometimes adapted to local phonology (e.g.GermanSilizium,Turkishsilisyum,Catalansilici,ArmenianՍիլիցիում orSilitzioum). A few others use instead acalque of the Latin root (e.g.Russianкремний, fromкремень "flint";Greekπυρίτιο fromπυρ "fire";Finnishpii frompiikivi "flint",Czechkřemík fromkřemen "quartz", "flint").[21]
Single crystal of silicon grown by theCzochralski process used to make integrated circuits
Silicon in its more common crystalline form was not prepared until 31 years later, byDeville.[29] Passing silicon chloride vapors over pure aluminum produced pure, hard octahedral crystals.[30]Friedrich Wöhler discovered the first volatile hydrides of silicon, synthesisingtrichlorosilane in 1857 andsilane itself in 1858, but a detailed investigation of thesilanes was only carried out in the early 20th century byAlfred Stock, despite early speculation on the matter dating as far back as the beginnings of synthetic organic chemistry in the 1830s.[31][32] Similarly, the firstorganosilicon compound, tetraethylsilane, was synthesised byCharles Friedel andJames Crafts in 1863, but detailed characterisation of organosilicon chemistry was only done in the early 20th century byFrederic Kipping.[19]
TheMOSFET, also known as the MOS transistor, is the key component of the Silicon Age. The first silicon semiconductor oxide planar transistor was made by Frosch and Derick in 1957.[39]
The "Silicon Age" refers to the late 20th century to early 21st century.[41][42][43] This is due to silicon being the dominant material used in electronics and information technology (also known as theDigital Age orInformation Age), similar to how theStone Age,Bronze Age andIron Age were defined by the dominant materials during their respectiveages of civilization.[41]
A silicon atom has fourteenelectrons. In the ground state, they are arranged in the electron configuration [Ne]3s23p2. Of these, four arevalence electrons, occupying the 3s orbital and two of the 3p orbitals. Like the other members of its group, the lightercarbon and the heaviergermanium,tin, andlead, it has the same number of valence electrons as valence orbitals: hence, it can complete itsoctet and obtain the stablenoble gas configuration ofargon by formingsp3 hybrid orbitals, forming tetrahedralSiX 4 derivatives where the central silicon atom shares an electron pair with each of the four atoms it is bonded to.[46] The first fourionisation energies of silicon are 786.3, 1576.5, 3228.3, and 4354.4 kJ/mol respectively; these figures are high enough to preclude the possibility of simple cationic chemistry for the element. Followingperiodic trends, its single-bond covalent radius of 117.6 pm is intermediate between those of carbon (77.2 pm) and germanium (122.3 pm). The hexacoordinate ionic radius of silicon may be considered to be 40 pm, although this must be taken as a purely notional figure given the lack of a simpleSi4+ cation in reality.[47]
At standard temperature and pressure, silicon is a shinysemiconductor with a bluish-grey metallic lustre; as typical for semiconductors, its resistivity drops as temperature rises. This arises because silicon has a small energy gap (band gap) between its highest occupied energy levels (the valence band) and the lowest unoccupied ones (the conduction band). TheFermi level is about halfway between thevalence and conduction bands and is the energy at which a state is as likely to be occupied by an electron as not. Hence pure silicon is effectively an insulator at room temperature. However,doping silicon with apnictogen such asphosphorus,arsenic, orantimony introduces one extra electron per dopant and these may then be excited into the conduction band either thermally or photolytically, creating ann-type semiconductor. Similarly, doping silicon with agroup 13 element such asboron,aluminium, orgallium results in the introduction of acceptor levels that trap electrons that may be excited from the filled valence band, creating ap-type semiconductor.[48] Joining n-type silicon to p-type silicon creates ap–n junction with a common Fermi level; electrons flow from n to p, while holes flow from p to n, creating a voltage drop. This p–n junction thus acts as adiode that can rectify alternating current that allows current to pass more easily one way than the other. Atransistor is an n–p–n junction, with a thin layer of weakly p-type silicon between two n-type regions. Biasing the emitter through a small forward voltage and the collector through a large reverse voltage allows the transistor to act as atriode amplifier.[48]
Silicon crystallises in a giant covalent structure at standard conditions, specifically in adiamond cubic crystal lattice (space group 227). It thus has a high melting point of 1414 °C, as a lot of energy is required to break the strong covalent bonds and melt the solid. Upon melting silicon contracts as the long-range tetrahedral network of bonds breaks up and the voids in that network are filled in, similar to water ice when hydrogen bonds are broken upon melting. It does not have any thermodynamically stable allotropes at standard pressure, but several other crystal structures are known at higher pressures. The general trend is one of increasingcoordination number with pressure, culminating in ahexagonal close-packed allotrope at about 40 gigapascals known as Si–VII (the standard modification being Si–I). An allotrope called BC8 (or bc8), having abody-centred cubic lattice with eight atoms per primitive unit cell (space group 206), can be created at high pressure and remains metastable at low pressure. Its properties have been studied in detail.[49]
Silicon boils at 3265 °C: this, while high, is still lower than the temperature at which its lighter congenercarbon sublimes (3642 °C) and silicon similarly has a lowerheat of vaporisation than carbon, consistent with the fact that the Si–Si bond is weaker than the C–C bond.[50]
Twenty-tworadioisotopes have been characterized, the two stablest being32Si with ahalf-life of about 157 years, and31Si with a half-life of 2.62 hours. All the remainingradioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half-lives that are less than one-tenth of a second.[13]32Si undergoes low-energybeta decay to32P and then stable32S.31Si may be produced by theneutron activation of natural silicon and is thus useful for quantitative analysis; it can be easily detected by its characteristic beta decay to stable31P, in which the emitted electron carries up to 1.48 MeV of energy.[31]
Silicon can enter the oceans through groundwater andriverine transport. Large fluxes of groundwater input have an isotopic composition which is distinct from riverine silicon inputs. Isotopic variations in groundwater and riverine transports contribute to variations in oceanic30Si values. Currently, there are substantial differences in the isotopic values of deep water in the world'socean basins. Between the Atlantic and Pacific oceans, there is a deep water30Si gradient of greater than 0.3 parts per thousand.30Si is most commonly associated with productivity in the oceans.[58]
Crystalline bulk silicon is rather inert, but becomes more reactive at high temperatures. Like its neighbour aluminium, silicon forms a thin, continuous surface layer ofsilicon dioxide (SiO 2) that protects the material beneath from oxidation. Because of this, silicon does not measurably react with the air below 900 °C. Between 950 °C and 1160 °C, the formation rate of thevitreous dioxide rapidly increases, and when 1400 °C is reached, atmosphericnitrogen also reacts to give the nitrides SiN andSi 3N 4. Silicon reacts with gaseoussulfur at 600 °C and gaseousphosphorus at 1000 °C. This oxide layer nevertheless does not prevent reaction with thehalogens;fluorine attacks silicon vigorously at room temperature,chlorine does so at about 300 °C, andbromine andiodine at about 500 °C. Silicon does not react with most aqueous acids, but is oxidised and complexed byhydrofluoric acid mixtures containing eitherchlorine ornitric acid to formhexafluorosilicates. It readily dissolves in hot aqueous alkali to formsilicates.[60] At high temperatures, silicon also reacts withalkyl halides; this reaction may be catalysed bycopper to directly synthesiseorganosilicon chlorides as precursors tosilicone polymers. Upon melting, silicon becomes extremely reactive, alloying with most metals to formsilicides, and reducing most metal oxides because theheat of formation of silicon dioxide is so large. In fact, molten silicon reacts virtually with every known kind of crucible material (except its own oxide,SiO 2).[61]: 13 This happens due to silicon's high binding forces for the light elements and to its high dissolving power for most elements.[61]: 13 As a result, containers for liquid silicon must be made ofrefractory, unreactive materials such aszirconium dioxide or group 4, 5, and 6 borides.[50][62]
Tetrahedral coordination is a major structural motif in silicon chemistry just as it is for carbon chemistry. However, the 3p subshell is rather more diffuse than the 2p subshell and does not hybridise so well with the 3s subshell. As a result, the chemistry of silicon and its heavier congeners shows significant differences from that of carbon,[63] and thus octahedral coordination is also significant.[64] For example, theelectronegativity of silicon (1.90) is much less than that of carbon (2.55), because the valence electrons of silicon are further from the nucleus than those of carbon and hence experience smaller electrostatic forces of attraction from the nucleus. The poor overlap of 3p orbitals also results in a much lower tendency towardcatenation (formation of Si–Si bonds) for silicon than for carbon, due to the concomitant weakening of the Si–Si bond compared to the C–C bond:[65] the average Si–Si bond energy is approximately 226 kJ/mol, compared to a value of 356 kJ/mol for the C–C bond.[66] This results in multiply bonded silicon compounds generally being much less stable than their carbon counterparts, an example of thedouble bond rule. On the other hand, the presence of radial nodes in the 3p orbitals of silicon suggests the possibility ofhypervalence, as seen in five and six-coordinate derivatives of silicon such asSiX− 5 andSiF2− 6.[67][65] Lastly, because of the increasing energy gap between the valence s and p orbitals as the group is descended, the divalent state grows in importance from carbon to lead, so that a few unstable divalent compounds are known for silicon; this lowering of the main oxidation state, in tandem with increasing atomic radii, results in an increase of metallic character down the group. Silicon already shows some incipient metallic behavior, particularly in the behavior of its oxide compounds and its reaction with acids as well as bases (though this takes some effort), and is hence often referred to as ametalloid rather than a nonmetal.[65] Germanium shows more, and tin is generally considered a metal.[19]
Silicon shows clear differences from carbon. For example,organic chemistry has very few analogies with silicon chemistry, whilesilicate minerals have a structural complexity unseen inoxocarbons.[68] Silicon tends to resemble germanium far more than it does carbon, and this resemblance is enhanced by thed-block contraction, resulting in the size of the germanium atom being much closer to that of the silicon atom than periodic trends would predict.[69] Nevertheless, there are still some differences because of the growing importance of the divalent state in germanium compared to silicon. Additionally, the lower Ge–O bond strength compared to theSi–O bond strength results in the absence of "germanone" polymers that would be analogous to silicone polymers.[66]
Silicon is the eighthmost abundant element in the universe, coming afterhydrogen,helium,oxygen,carbon,neon,iron, andnitrogen. This differs fromabundance of elements in Earth's crust due to substantial separation of the elements taking place during the formation of theSolar System. Silicon makes up 27.2% of the Earth's crust by weight, second only to oxygen at 45.5%, with which it always is associated in nature. Further fractionation took place in the formation of the Earth byplanetary differentiation:Earth's core, which makes up 31.5% of the mass of the Earth, has approximate compositionFe 25Ni 2Co 0.1S 3; themantle makes up 68.1% of the Earth's mass and is composed mostly of denser oxides and silicates, an example beingolivine,(Mg,Fe) 2SiO 4; while the lighter siliceous minerals such asaluminosilicates rise to the surface and form the crust, making up 0.4% of the Earth's mass.[70][71]
The crystallisation ofigneous rocks from magma depends on a number of factors; among them are the chemical composition of the magma, the cooling rate, and some properties of the individual minerals to be formed, such aslattice energy, melting point, and complexity of their crystal structure. As magma is cooled,olivine appears first, followed bypyroxene,amphibole,biotite mica,orthoclase feldspar,muscovite mica,quartz,zeolites, and finally, hydrothermal minerals. This sequence shows a trend toward increasingly complex silicate units with cooling, and the introduction ofhydroxide andfluoride anions in addition to oxides. Many metals may substitute for silicon. After these igneous rocks undergoweathering, transport, and deposition,sedimentary rocks like clay, shale, and sandstone are formed.Metamorphism also may occur at high temperatures and pressures, creating an even vaster variety of minerals.[70]
There are four sources for silicon fluxes into the ocean: chemical weathering of continental rocks, river transport, dissolution of continental terrigenous silicates, and the reaction between submarine basalts and hydrothermal fluid which release dissolved silicon. All four of these fluxes are interconnected in the ocean's biogeochemical cycle as they all were initially formed from the weathering of Earth's crust.[72]
Approximately 300–900 megatonnes ofaeolian dust is deposited into the world's oceans each year. Of that value, 80–240 megatonnes are in the form of particulate silicon. The total amount of particulate silicon deposition into the ocean is still less than the amount of silicon influx into the ocean via riverine transportation.[73] Aeolian inputs of particulate lithogenic silicon into the North Atlantic and Western North Pacific oceans are the result of dust settling on the oceans from the Sahara and Gobi Desert, respectively.[72] Riverine transports are the major source of silicon influx into the ocean in coastal regions, while silicon deposition in the open ocean is greatly influenced by the settling of aeolian dust.[73]
This reaction, known as carbothermal reduction of silicon dioxide, usually is conducted in the presence of scrap iron with low amounts ofphosphorus andsulfur, producingferrosilicon.[31] Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental silicon, providing 4.6 milliontonnes (or two-thirds of world output) of silicon, most of it in the form of ferrosilicon. It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t), and the United States (170,000 t).[74] Ferrosilicon is primarily used by the iron and steel industry (seebelow) with primary use as alloying addition in iron or steel and for de-oxidation of steel in integrated steel plants.[31]
Another reaction, sometimes used, is aluminothermal reduction of silicon dioxide, as follows:[75]
3SiO 2 + 4 Al → 3 Si + 2Al 2O 3
Leaching powdered 96–97% pure silicon with water results in ~98.5% pure silicon, which is used in the chemical industry. However, even greater purity is needed for semiconductor applications, and this is produced from the reduction oftetrachlorosilane (silicon tetrachloride) ortrichlorosilane. The former is made by chlorinating scrap silicon and the latter is a byproduct ofsilicone production. These compounds are volatile and hence can be purified by repeatedfractional distillation, followed by reduction to elemental silicon with very purezinc metal as the reducing agent. The spongy pieces of silicon thus produced are melted and then grown to form cylindrical single crystals, before being purified byzone refining. Other routes use the thermal decomposition ofsilane ortetraiodosilane (SiI 4). Another process used is the reduction ofsodium hexafluorosilicate, a common waste product of the phosphate fertilizer industry, by metallicsodium: this is highly exothermic and hence requires no outside energy source. Hyperfine silicon is made at a higher purity than almost any other material:transistor production requires impurity levels in silicon crystals less than 1 part per 1010, and in special cases impurity levels below 1 part per 1012 are needed and attained.[31]
Silicon nanostructures can directly be produced from silica sand using conventional metalothermic processes, or the combustion synthesis approach. Such nanostructured silicon materials can be used in various functional applications including the anode of lithium-ion batteries (LIBs), other ion batteries, future computing devices like memristors or photocatalytic applications.[76]
Most silicon is used industrially without being purified, often with comparatively little processing from its natural form. More than 90% of the Earth's crust is composed ofsilicate minerals, which are compounds of silicon and oxygen, often with metallic ions when negatively charged silicate anions require cations to balance the charge. Many of these have direct commercial uses, such as clays,silica sand, and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). Silicates are used in makingPortland cement (made mostly of calcium silicates) which is used inbuilding mortar and modernstucco, but more importantly, combined with silica sand, and gravel (usually containing silicate minerals such as granite), to make theconcrete that is the basis of most of the very largest industrial building projects of the modern world.[77]
Silica is used to makefire brick, a type of ceramic. Silicate minerals are also in whitewareceramics, an important class of products usually containing various types of firedclay minerals (natural aluminium phyllosilicates). An example isporcelain, which is based on the silicate mineralkaolinite. Traditionalglass (silica-basedsoda–lime glass) also functions in many of the same ways, and also is used for windows and containers. In addition, specialty silica basedglass fibers are used foroptical fiber, as well as to producefiberglass for structural support andglass wool forthermal insulation.
Elemental silicon is added to moltencast iron asferrosilicon or silicocalcium alloys to improve performance in casting thin sections and to prevent the formation ofcementite where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is grossly impure, it accounts for 80% of the world's use of free silicon. Silicon is an important constituent oftransformer steel, modifying itsresistivity andferromagnetic properties.
The properties of silicon may be used to modify alloys with metals other than iron. "Metallurgical grade" silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminium-silicon alloys (silumin alloys) for aluminium partcasts, mainly for use in theautomotive industry. Silicon's importance in aluminium casting is that a significantly high amount (12%) of silicon in aluminium forms aeutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity. Silicon also significantly improves the hardness and thus wear-resistance of aluminium.[80][81] Metallurgical grade silicon is made by melting quartz or quartzite in a large arc furnace, in a carbothermal reduction process with carbon-containing material such as coal, coke or charcoal and woodchips for gas circulation. This production technique without iron is often used forpolysilicon production for photovoltaics and also semiconductors.[82][83][84][85]
Most elemental silicon produced remains as a ferrosilicon alloy, and only approximately 20% is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). An estimated 15% of the world production of metallurgical grade silicon is further refined to semiconductor purity.[81] This typically is the "nine-9" or 99.9999999% purity,[86] nearly defect-free singlecrystalline material.[87]
Silicon wafer which has been thermally oxidized using water vapor at 1100º C for ~30 nm of silicon dioxide. The clear regions have been etched bare for subsequent doping.
In commonintegrated circuits, a wafer of mono-crystalline silicon (Si) serves as a mechanical support for the circuits. Circuit elements (transistors) are created by doping and passivated by thin layers ofsilicon oxide, an insulator that is easily produced on Si surfaces by processes ofthermal oxidation orchemical vapor deposition (CVD) (among other methods). Thermal oxidation is most common and involves exposing Si to oxygen under the specific conditions. The resulting oxide thickness can be predicted by theDeal–Grove model. Silicon is the most popular material for integrated circuits due to the high stability and ease of forming its native oxide (SiO2). The insulating oxide of silicon is not soluble in water, which gives it an advantage overgermanium.[91] Germanium (Ge) was used for the first version of the transistor and has similar electronic properties to silicon such as carriermobility andband gap. However Ge based technologies ultimately failed due to the instability of the GeO2. Germanium is still used in modern semiconductor electronics as adopant to enhance the mobility ofholes in the source and drain ofPMOS.
Monocrystalline silicon is expensive to produce, and is usually justified only in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon may be employed. These includehydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) used in the production of low-cost,large-area electronics in applications such asliquid crystal displays and of large-area, low-cost, thin-filmsolar cells. Such semiconductor grades of silicon are either slightly less pure or polycrystalline rather than monocrystalline, and are produced in comparable quantities as the monocrystalline silicon: 75,000 to 150,000 metric tons per year. The market for the lesser grade is growing more quickly than for monocrystalline silicon. By 2013, polycrystalline silicon production, used mostly in solar cells, was projected to reach 200,000 metric tons per year, while monocrystalline semiconductor grade silicon was expected to remain less than 50,000 tons per year.[81]
Silicon quantum dots are created through the thermal processing of hydrogensilsesquioxane into nanocrystals ranging from a few nanometers to a few microns, displaying size dependentluminescent properties.[92][93] The nanocrystals display largeStokes shifts converting photons in the ultraviolet range to photons in the visible or infrared, depending on the particle size, allowing for applications inquantum dot displays andluminescent solar concentrators due to their limited self absorption. A benefit of using silicon basedquantum dots overcadmium orindium is the non-toxic, metal-free nature of silicon.[94][95]Another application of silicon quantum dots is for sensing of hazardous materials. The sensors take advantage of the luminescent properties of the quantum dots throughquenching of thephotoluminescence in the presence of the hazardous substance.[96] There are many methods used for hazardous chemical sensing with a few being electron transfer,fluorescence resonance energy transfer, and photocurrent generation.[97] Electron transfer quenching occurs when thelowest unoccupied molecular orbital (LUMO) is slightly lower in energy than the conduction band of the quantum dot, allowing for the transfer of electrons between the two, preventing recombination of the holes and electrons within the nanocrystals. The effect can also be achieved in reverse with a donor molecule having itshighest occupied molecular orbital (HOMO) slightly higher than a valence band edge of the quantum dot, allowing electrons to transfer between them, filling the holes and preventing recombination. Fluorescence resonance energy transfer occurs when a complex forms between the quantum dot and a quencher molecule. The complex will continue to absorb light but when the energy is converted to the ground state it does not release a photon, quenching the material. The third method uses different approach by measuring thephotocurrent emitted by the quantum dots instead of monitoring the photoluminescent display. If the concentration of the desired chemical increases then the photocurrent given off by the nanocrystals will change in response.[98]
Solid or molten silicon offers much higher storage temperatures than salts with consequent greater capacity and efficiency. It is being researched as a possible more energy efficient storage technology. Silicon is able to store more than 1 MWh of energy per cubic meter at 1400 °C. An additional advantage is the relative abundance of silicon when compared to the salts used for the same purpose.[99][100]
Hot silicon thermal energy storing technology would be able to store significant thermal energy at extremely high temperatures (around 1400-2000 °C). This would be utilized by using the white hot molten silicon to store excess electricity generated from surrounding renewable sources like solar energy and wind power. This system would enable efficient, lower costing, and a longer duration of energy storage compared to other sensible heat storage options.[101]
Although silicon is readily available in the form ofsilicates, very few organisms use it directly.Diatoms,radiolaria, andsiliceous sponges usebiogenic silica as a structural material for their skeletons. Some plants accumulate silica in their tissues and require silicon for their growth, for examplerice. Silicon may be taken up by plants asorthosilicic acid (also known as monosilicic acid) and transported through thexylem, where it forms amorphous complexes with components of the cell wall. This has been shown to improve cell wall strength and structural integrity in some plants, thereby reducing insect herbivory and pathogenic infections. In certain plants, silicon may also upregulate the production of volatile organic compounds and phytohormones which play a significant role in plant defense mechanisms.[102][103][104] In more advanced plants, silica (opal)phytoliths provide structural support.[105][106][103]
Severalhorticultural crops are known to protect themselves againstfungal plant pathogens with silica, to such a degree thatfungicide application may fail unless accompanied by sufficient silicon nutrition. Silicaceous plant defense molecules activate somephytoalexins, meaning some of them are signalling substances producingacquired immunity. When deprived, some plants will substitute with increased production of other defensive substances.[103]
Life on Earth is largely composed ofcarbon, butastrobiology considers thatextraterrestrial life may have otherhypothetical types of biochemistry. Silicon is considered an alternative to carbon, as it can create complex and stable molecules with four covalent bonds, required for aDNA-analog, and it is available in large quantities.[107]
Diatoms use silicon in thebiogenic silica (bSi) form,[108] which is taken up by the silicon transport protein (SIT) to be predominantly used in the cell wall structure as frustules.[109] Silicon enters the ocean in a dissolved form such as silicic acid or silicate.[110] Since diatoms are one of the main users of these forms of silicon, they contribute greatly to the concentration of silicon throughout the ocean. Silicon forms a nutrient-like profile in the ocean due to the diatom productivity in shallow depths.[110] Therefore, concentration of silicon is lower in the shallow ocean and higher in the deep ocean.
Diatom productivity in the upper ocean contributes to the amount of silicon exported to the lower ocean.[111] When diatom cells arelysed in the upper ocean, their nutrients such as iron, zinc, and silicon, are brought to the lower ocean through a process calledmarine snow. Marine snow involves the downward transfer of particulate organic matter by vertical mixing of dissolved organic matter.[112] It has been suggested that silicon is considered crucial to diatom productivity and as long as there is silicic acid available for diatoms to use, the diatoms can contribute to other important nutrient concentrations in the deep ocean as well.[113]
In coastal zones, diatoms serve as the major phytoplanktonic organisms and greatly contribute to biogenic silica production. In the open ocean, however, diatoms have a reduced role in global annual silica production. Diatoms in North Atlantic and North Pacific subtropical gyres only contribute about 5–7% of global annual marine silica production. TheSouthern Ocean produces about one-third of global marine biogenic silica.[72] The Southern Ocean is referred to as having a "biogeochemical divide"[114] since only minuscule amounts of silicon are transported out of this region.
There is some evidence that silicon is important to human health for their nail, hair, bone, and skin tissues,[115] for example, in studies that demonstrate that premenopausal women with higher dietary silicon intake have higherbone density, and that silicon supplementation can increase bone volume and density in patients withosteoporosis.[116] Silicon is needed for synthesis ofelastin andcollagen, of which theaorta contains the greatest quantity in the human body,[117] and has been considered anessential element;[118] nevertheless, it is difficult to prove its essentiality, because silicon is very common, and hence, deficiency symptoms are difficult to reproduce.[119][120]
Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)."[121][122]
^Althoughcarbon remains solid at higher temperatures than silicon, itsublimes atatmospheric pressure instead of melting and boiling, so it has no melting point and boiling point.
^abcArblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Weeks, Mary Elvira (1932). "The discovery of the elements: XII. Other elements isolated with the aid of potassium and sodium: beryllium, boron, silicon, and aluminum".Journal of Chemical Education.9 (8):1386–1412.Bibcode:1932JChEd...9.1386W.doi:10.1021/ed009p1386.
^Voronkov, M. G. (2007). "Silicon era".Russian Journal of Applied Chemistry.80 (12): 2190.doi:10.1134/S1070427207120397.
^In his table of the elements, Lavoisier listed five "salifiable earths",i.e., ores that could be made to react with acids to produce salts (salis = salt, in Latin):chaux (calcium oxide),magnésie (magnesia, magnesium oxide),baryte (barium sulfate),alumine (alumina, aluminium oxide), andsilice (silica, silicon dioxide). About these "elements", Lavoisier speculates: "We are probably only acquainted as yet with a part of the metallic substances existing in nature, as all those which have a stronger affinity to oxygen than carbon possesses, are incapable, hitherto, of being reduced to a metallic state, and consequently, being only presented to our observation under the form of oxyds, are confounded with earths. It is extremely probable that barytes, which we have just now arranged with earths, is in this situation; for in many experiments it exhibits properties nearly approaching to those of metallic bodies. It is even possible that all the substances we call earths may be only metallic oxyds, irreducible by any hitherto known process." – fromLavoisier (1799).Elements of Chemistry. Translated by Robert Kerr (4 ed.). Edinburgh, Scotland: William Creec. p. 218. (The original passage appears in:Lavoisier (1789).Traité Élémentaire de Chimie. Vol. 1. Paris: Cuchet. p. 174.)
^Thomson, Thomas; Baldwin, Charles; Blackwood, William; Baldwin, Cradock; Bell & Bradfute, bookseller; Hodges & McArthur, bookseller (1817).A system of chemistry: in four volumes. University of Wisconsin - Madison. London : Printed for Baldwin, Craddock, and Joy, Paternoster-Row; William Blackwood, and Bell and Bradfute, Edinburgh; and Hodges and Macarthur, Dublin. p. 252.: "The base of silica has been usually considered as a metal, and calledsilicium. But as there is not the smallest evidence for its metallic nature, and as it bears a close resemblance to boron and carbon, it is better to class it along with these bodies, and to give it the name ofsilicon."
Berzelius announced his discovery of silicon ("silicium") in: Berzelius, J. (presented: 1823; published: 1824)"Undersökning af flusspatssyran och dess märkvärdigaste föreningar" (Investigation of hydrofluoric acid and of its most noteworthy compounds),Kongliga Vetenskaps-Academiens Handlingar [Proceedings of the Royal Science Academy],12 : 46–98. The isolation of silicon and its characterization are detailed in the section titled "Flussspatssyrad kisseljords sönderdelning med kalium," pp. 46–68.
The above article was reprinted in French in: Berzelius (1824)"Décomposition du fluate de silice par le potassium" (Decomposition of silica fluoride by potassium),Annales de Chimie et de Physique,27: 337–359.
^Weeks, Mary Elvira (1932). "The discovery of the elements: XII. Other elements isolated with the aid of potassium and sodium: beryllium, boron, silicon, and aluminum".Journal of Chemical Education.9 (8):1386–1412.Bibcode:1932JChEd...9.1386W.doi:10.1021/ed009p1386.
^Koch, E.C.; Clement, D. (2007). "Special Materials in Pyrotechnics: VI. Silicon – An Old Fuel with New Perspectives".Propellants, Explosives, Pyrotechnics.32 (3):205–212.doi:10.1002/prep.200700021.
^Walsh, Tim (2005)."Silly Putty".Timeless toys: classic toys and the playmakers who created them. Andrews McMeel Publishing.ISBN978-0-7407-5571-2.
^Troszak T.A. (2021) The hidden costs of solar photovoltaic power, NATO ENSEC COE Energy highlights Vol 16, pp 22. Copyright 2021 NATO Energy Security Center of Excellence
^"Semi" SemiSource 2006: A supplement to Semiconductor International. December 2005. Reference Section:How to Make a Chip. Adapted from Design News. Reed Electronics Group.
^SemiSource 2006: A supplement to Semiconductor International. December 2005. Reference Section:How to Make a Chip. Adapted from Design News. Reed Electronics Group.
^Kim, Sang Gyu; Kim, Ki Woo; Park, Eun Woo; Choi, Doil (2002). "Silicon-Induced Cell Wall Fortification of Rice Leaves: A Possible Cellular Mechanism of Enhanced Host Resistance to Blast".Phytopathology.92 (10):1095–103.Bibcode:2002PhPat..92.1095K.doi:10.1094/PHYTO.2002.92.10.1095.PMID18944220.
^Rahman, Atta-ur- (2008). "Silicon".Studies in Natural Products Chemistry. Vol. 35. Elsevier Science. p. 856.ISBN978-0-444-53181-0.
^Exley, C. (1998). "Silicon in life:A bioinorganic solution to bioorganic essentiality".Journal of Inorganic Biochemistry.69 (3):139–144.doi:10.1016/S0162-0134(97)10010-1.
^Aguilera Mochón, Juan Antonio (2016).La vida no terrestre [The non-terrestrial life] (in Spanish). RBA. pp. 43–45.ISBN978-84-473-8665-9.
^Martin, Keith R. (2013). "Silicon: The Health Benefits of a Metalloid". In Astrid Sigel; Helmut Sigel; Roland K.O. Sigel (eds.).Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. Vol. 13. Springer. pp. 451–473.doi:10.1007/978-94-007-7500-8_14.ISBN978-94-007-7499-5.PMID24470100.
^Loeper, J.; Fragny, M. (1978). "The Physiological Role of the Silicon and its AntiAtheromatous Action".Biochemistry of Silicon and Related Problems. pp. 281–296.doi:10.1007/978-1-4613-4018-8_13.ISBN978-1-4613-4020-1.
^Lippard, Stephen J.; Jeremy M. Berg (1994).Principles of Bioinorganic Chemistry. Mill Valley, CA: University Science Books. p. 411.ISBN978-0-935702-72-9.
^"AAPFCO Board of Directors 2006 Mid-Year Meeting"(PDF). Association of American Plant Food Control Officials. Archived fromthe original(PDF) on 6 January 2012. Retrieved2011-07-18.A presentation was made for Excell Minerals to recognize Silicon as a recognized plant nutrient
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