silicon

[guī]

chemical element

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Silicon is a chemical element , the chemical symbol is Si , old name silicon 。 Atomic number 14, Relative atomic mass 28.0855. It is a hard and brittle crystalline solid, which is a tetravalent quasi metal and semiconductor 。 With amorphous silicon and Crystalline silicon Two allotropes belonging to periodic table of ele ments Upper third cycle, IVA family Metalloid element 。

Silicon is also a very common element silicate or silicon dioxide Is widely found in rocks gravel 、 dust in Silicon ranks eighth in the universe. It is widely distributed in dust, sand, planets and planets in various forms of silica (silicate) or silicate. Crust More than 90% of them are silicate minerals, making silicon the second highest element in the crust (about 28% by mass), second only to oxygen^[1] 。

Chinese name: silicon
Foreign name: silicon
Element symbol: Si
Atomic weight: twenty-eight point zero eight five five
Element Type: Metalloid
Atomic number: fourteen
Discoverer: Jns Jakob Berzelius
Cycle: Third cycle
family: Family IV A
area: Zone p
Electronic layout: [Ne]3s two 3p two
CAS login number: 7440-21-3^[1]

EINECS login number: 231-130-8^[1]
Density: 2.33 g/cm³^[1]
Melting point: 1410 ℃^[1]
Boiling point: 2355 ℃^[1]
Saturated vapor pressure: 9.999Pa^[1]
Solubility: Insoluble in water and acid solution; Soluble in alkaline solution
Appearance and character: Dark brown amorphous powder
stability: Stable, fine powder highly flammable. It is incompatible with oxidant, alkali, carbonate, alkali metal, lead and aluminum oxide, halogen, carbide and formic acid.
Security description: S16; S33; S7/9
Hazard description: R11
UN dangerous goods number: two thousand nine hundred and twenty-two

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A brief history of discovery

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In 1787, Lavoisier First discovery of silicon in rocks^[2] 。

In 1800, David mistook it for a compound^[2] 。

1811 Guy Lussac (Gay Lussac) and Thénard (Thenard, Louis Jacques) Heating potassium and Silicon tetrafluoride Get impure Amorphous silicon , according to Latin silex（ Flint ）Named as silicon^[1] ； In the same year, Gay Lussac and Thenard reacted with silicon tetrafluoride and alkaline earth metal, and found that a reddish brown compound (possibly amorphous silicon containing impure matter) was formed during the reaction^[3] 。

In 1823, silicon was first used as an element by Swedish chemists Bezelius (J ö nsJacob Berzelius) found that amorphous silicon was refined by the same method as Gay Lussac one year later; Then, the simple silicon is purified by repeated cleaning; In the same year, Bezelius added silica powder iron ， carbon The mixture of FESi 。 However, in order to extract pure silicon, Bezelius uses silicon fluoride calcium compounds, the solid obtained after dry burning, and water decomposition to obtain pure silicon^[3] 。

In 1824, in Stockholm, Bezelius obtained silicon by heating potassium fluosilicate and potassium. This product is Potassium silicate Pollution, but he put it in water and stirred it. Because water will react with it, relatively pure silicon powder is obtained, so the honor of finding silicon belongs to Bezelius^[3] 。

1824 J J. Bezelius uses the same method to remove Fluosilicic acid , obtaining pure amorphous silicon^[3] 。

It was not until 1854 that crystalline silicon was refined; In the same year, H S. C. Dewell also made crystalline silicon for the first time^[2] 。

Origin of the name of silicon: English silicon, from the Latin word "silicon", meaning flint (flint). At the beginning of the Republic of China, scholars originally translated this element as "silicon" and made it read "xi (Guipang can read the sound of xi)" (again, the word "silicon" was a variant of the word "gua", read hua). However, at that time, because the Pinyin scheme had not been popularized, most people misread it as gui. The Chemical Society noticed this problem, so it created the word "Si" to avoid misreading. In February 1953, the Chinese mainland, Chinese Academy of Sciences A nationwide symposium on the naming of chemical substances was held. Some scholars changed their name back to "silicon" and read "gui" after announcing that the homonym of "silicon" and other chemical elements "tin" and "selenium" was easily confused, but they did not realize that the word "silicon" should also read xi. In Hong Kong, both methods are available, but "silicon" is more common.

Source and distribution

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Silicon exists in sunlight and fixed star And is the main component of a class of materials called "meteorites". It is also ilmenite Composition of, for industrial use carbon Electrodes are heated in an electric furnace silicon dioxide And carbon to prepare silicon. After amorphous silicon is made into brown powder, it can be easily melted or vaporized^[1] 。 Crystalline silicon It has metallic luster and light gray. As an element, silicon is second only to oxygen in concentration on the earth, but only ranks eighth in the whole universe. Silicon is used as a standard (Si=1) to measure the abundance 。

In nature, silicon does not exist as a single substance, but mainly as oxide and silicate Exists in the form of. The simplest is the compound SiO of silicon and oxygen two 。 Quartz, crystal, etc. are variants of pure silica. Silicon oxide compounds in ores and rocks silicate , the common ones are feldspar KAlSi three O eight 、 kaolin Al two Si two O five (OH) four 、 talc Mg three (Si four O ten )(OH) two 、 mica KAl two (AlSi three O ten )(OH) two 、 asbestos H four Mg three Si two O nine 、 Natrolite Na two (Al two Si three O ten )·2H two O、 Garnet Ca three Al two (SiO four ) three , zircon ZrSiO four and Beryl Be three Al two Si six O eighteen Etc. Soil Clay and Sand Is a natural silicate rock weathering Post product^[2] 。

Physical and chemical properties

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physical property

yes Amorphous silicon And crystalline silicon Allotrope 。 Crystal silicon is grayish black, density 2.32-2.34 g/cm three , melting point 1410 ℃, boiling point 2355 ℃, crystalline silicon belongs to atomic crystal. It is insoluble in water, nitric acid and hydrochloric acid, but soluble in hydrofluoric acid and alkali liquor. Hard and metallic.

Physical properties of silicon
series	Metalloid
family	Group IVA
cycle	three
Element partition	Zone p
Common valence	-4，+4
hardness	six point five
Crustal content	25.7%
Modulus of elasticity	190GPa
density	2.33g/cm³（18℃）
melting point	1410℃
boiling point	2355℃
Heat of vaporization	384.22 kJ/mol
saturated Vapor pressure^[4]	0.13kPa（1724 ℃）
critical pressure^[4]	53.6MPa
conductivity	2.52×10 -4 /(m ohm)
Electronegativity	1.90（ Pauling scale ）
specific heat	700 J/（kg·K）

Atomic attribute^[5]

External electron arrangement: 1s ² 2s ² 2p ⁶ 3s ² 3p ²

Atomic weight: 28.0855u;

Nuclear defect mass: 0.1455u;

Atomic radius: (calculated value) 110 (111) pm;

Covalent radius: 111 pm;

Vander Waals radius ：210 pm；

Unit cell Type: cubic diamond;

Cell parameter: a=0.543087 nm measured at 20 ℃;

Color and appearance: dark gray with blue tone;

conductivity : The conductivity of silicon has a great relationship with its temperature. As the temperature rises, the conductivity increases, reaching the maximum at about 1480 ℃, and then increases with temperature Increase and decrease^[6] 。

Ionization energy of silicon
Electronegativity^[7]	1.90 (Pauling scale)
Thermal conductivity^[7]	148 W/（m·K）
First ionization energy^[7]	786.5 kJ/mol
Second ionization energy^[7]	1577.1 kJ/mol
Third ionization energy^[7]	3231.6 kJ/mol
Fourth ionization energy^[7]	4355.5 kJ/mol
Fifth ionization energy^[7]	16091 kJ/mol
Sixth ionization energy^[7]	19805 kJ/mol
Seventh ionization energy^[7]	23780 kJ/mol
Eighth ionization energy^[7]	29287 kJ/mol
Ninth ionization energy^[7]	33878 kJ/mol
Tenth ionization energy^[7]	38726 kJ/mol

isotope^[5]

Isotopes of silicon
Symbol	Z （ p ）	N （ n ）	Quality（ u ）	half life	Nucleus spin	relative abundance	Relative abundance Variation of
twenty-two Si	fourteen	eight	22.03453(22)#	29(2)ms	0+
twenty-three Si	fourteen	nine	23.02552(21)#	42.3(4)ms	3/2+#
twenty-four Si	fourteen	ten	24.011546(21)	140(8)ms	0+
twenty-five Si	fourteen	eleven	25.004106(11)	220(3)ms	5/2+
twenty-six Si	fourteen	twelve	25.992330(3)	2.234(13)s	0+
twenty-seven Si	fourteen	thirteen	26.98670491(16)	4.16(2)s	5/2+
twenty-eight Si	fourteen	fourteen	27.9769265325(19)	stable	0+	0.92223(19)	0.92205-0.92241
twenty-nine Si	fourteen	fifteen	28.976494700(22)	stable	1/2+	0.04685(8)	0.04678-0.04692
thirty Si	fourteen	sixteen	29.97377017(3)	stable	0+	0.03092(11)	0.03082-0.03102
thirty-one Si	fourteen	seventeen	30.97536323(4)	157.3(3)min	3/2+
thirty-two Si	fourteen	eighteen	31.97414808(5)	170(13)a	0+
thirty-three Si	fourteen	nineteen	32.978000(17)	6.18(18)s	（3/2+）
thirty-four Si	fourteen	twenty	33.978576(15)	2.77(20) s	0+
thirty-five Si	fourteen	twenty-one	34.98458(4)	780(120) ms	7/2-#
thirty-six Si	fourteen	twenty-two	35.98660(13)	0.45(6)s	0+
thirty-seven Si	fourteen	twenty-three	36.99294(18)	90(60)ms	（7/2-）#
thirty-eight Si	fourteen	twenty-four	37.99563(15)	90# ms	0+
thirty-nine Si	fourteen	twenty-five	39.00207(36)	47.5(20) ms	7/2-#
forty Si	fourteen	twenty-six	40.00587(60)	33.0(10) ms	0+
forty-one Si	fourteen	twenty-seven	41.01456(198)	20.0(25) ms	7/2-#
forty-two Si	fourteen	twenty-eight	42.01979(54)#	13(4) ms	0+
forty-three Si	fourteen	twenty-nine	43.02866(75)#	15# ms	3/2-#
forty-four Si	fourteen	thirty	44.03526(86)#	10# ms	0+

Remarks: 1 The data marked with # represents theoretical speculation without experimental proof, while the data enclosed in parentheses represents data uncertainty.

2. There are three natural stable isotopes Si-28 (92.2%), Si-29 (4.7%) and Si-30 (3.1%), as well as artificial radioisotopes with mass numbers of 25, 26, 27, 31 and 32^[1] 。

chemical property

Silicon has obvious non-metallic characteristics and can be dissolved in alkali metal hydroxide solution to form silicate and hydrogen 。

Silicon atom is located in the fourth main group of the periodic table. Its atomic number is 14, and there are 14 electrons outside the nucleus. The electrons are surrounded by layers outside the nucleus, from low silicon atoms to high silicon atoms according to energy levels, from inside to outside. The silicon atom has two electrons in the first layer and eight electrons in the second layer, reaching a stable state. There are four electrons in the outermost layer, which are called valence electrons Conductivity And other aspects play a leading role.

Because silicon atom has such a structure, it has some special properties: the four valence electrons on the outermost layer make silicon atoms covalently bond with each other, and silicon has a high melting point and density; The chemical properties are relatively stable, and it is difficult to react with other substances (except hydrogen fluoride and alkali liquor) at room temperature; The concentration of free electrons in silicon crystal is extremely low, and it can conduct electricity, but its conductivity is lower than that of metal, and it increases with temperature, so it has semiconductor properties.

Homogeneous under heating halogen , nitrogen, carbon, etc Nonmetal It can also react with some metals such as Mg, Ca, Fe, Pt, etc Silicide 。 Insoluble in general Inorganic acid Medium, soluble in alkali solution, and hydrogen is released to form corresponding alkali metal Silicate solution can interact with water vapor at high temperature.

Classification: Pure substance , single substance, non-metallic single substance.

(1) React with simple substance

(2) It can react with some oxides under high temperature and vacuum conditions

(3) React with acid: only react with hydrofluoric acid

(4) Reaction with alkali

Note: Silicon and aluminum are simple substances that can react with acid and alkali to release hydrogen.

Preparation method

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Laboratory preparation

In the laboratory, magnesium powder can be used to reduce the powder under red heat silicon dioxide , washed with dilute acid magnesium oxide and Magnesium powder , reuse hydrofluoric acid Wash the inactive silica to get silicon 。 The amorphous silicon produced by this method is not pure enough, which is brown black powder.

Industrial preparation

In industry, silicon dioxide is mixed with carbon in electric furnace by using carbon electrode（ coke ）Heat together to produce simple silicon:

The purity of the product is about 96-98%. Repeat leaching to form about 99.7% of the purified product. Or, convert low-grade silicon into its halide Or halogenated silane, and then reduce it with high-purity reducing agent. Ultrapure silicon for semiconductor applications can be manufactured by several methods. These processes include the reduction of silicon tetrachloride with high-purity zinc:

Or reduce trichlorosilane with hydrogen at 1150 ℃^[8] ：

Or heat silane or silicon tetraiodide to high temperature

Or by reducing silicon tetrafluoride with sodium:

application area

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Semiconductor field

High purity monocrystalline silicon is an important semiconductor material with a band gap of 1.2 eV. A small amount of Group IIIA elements are doped into the monocrystalline silicon to form a p-type silicon semiconductor; Trace VA group elements are doped to form n-type semiconductor. P-type semiconductor and n-type semiconductor combine to form p-n junction, which is the basic structure of semiconductor devices. It can be made into diodes, triodes, thyristors and various integrated circuits (including chips and CPUs in people's computers), and can also be made into solar photovoltaic cells to convert radiant energy into electrical energy.

Silicon is usually the preferred semiconductor because it is cheap and has a high melting point, which is very suitable for high-temperature applications. Silicon also has unique doping ability, which means that it can be deliberately polluted by other elements to change its electrical performance. This ability to control the electrical properties of silicon makes it the basis of modern electronic products, because it is the most commonly used material in the manufacture of computer chips or microprocessors. The manufacturing process involves depositing multiple layers of material, including silicon, to make necessary components, such as transistors, diodes, and resistors.

The use of silicon in computer chips has promoted the development of low-power and high-performance electronic devices, making them suitable for a wide range of applications, including computers, smart phones and other consumer electronic products. The ability to manufacture complex electronic circuits on a small area of silicon has completely changed the electronics industry, making it possible to develop smaller, faster, and more powerful electronic devices. With the progress of technology, silicon will only become more and more important in the industry, making it a key semiconductor material for future electronic products^[9] 。

Material field

Silicon can be used to make cermet composites. This material inherits the respective advantages of metal and ceramic, and also makes up for their shortcomings. It has the advantages of high temperature resistance, high toughness, and cutability. The first space shuttle Columbia was built with a silicon tile shell to withstand the high temperature caused by friction when the plane passed through the dense atmosphere at high speed.

Pure silica can be drawn into glass fiber with high transparency. This fiber is an important material for optical fiber communication. This communication method replaces the bulky cable, with high communication capacity, no electric and magnetic interference, no eavesdropping, and high confidentiality. Optical fiber communication has revolutionized human life.

Organic compounds of silicon combine the excellent inorganic properties of silicon with the properties of organic materials, making organic silicon compounds unique and opening up new fields. It has the basic properties of low surface tension, low viscosity temperature coefficient, high compressibility, high gas permeability, and has excellent characteristics such as high and low temperature resistance, electrical insulation, oxidation resistance stability, weather resistance, flame resistance, hydrophobic, corrosion resistance, non-toxic and tasteless, and physiological inertia. It is mainly used for sealing, bonding, lubrication, coating, surface activity, demoulding, defoaming, foam suppression, waterproof Damp proof, inert filling, etc^[10] 。

Agriculture

Silicon plays an important role in improving plant resistance to abiotic and biotic stresses. For example, silicon can improve plant resistance to drought, salt stress, ultraviolet radiation, diseases and pests. Silicon can improve the resistance of rice to rice leaf roller. After silicon application, the defense response of rice to insect feeding increases rapidly, and silicon plays an alert role in plant defense. When rice is attacked by pests, silicon can alert rice to quickly activate jasmonic acid pathway related to stress resistance. Jasmonic acid signal in turn promotes silicon absorption. Silicon and jasmonic acid signal pathway interact to affect rice resistance to pests^[11] 。

Physiological function

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Silicon is one of the essential trace elements for human body, accounting for 0.026% of body weight. Silicon is necessary in the formation of connective tissue and cartilage. Silicon can connect mucopolysaccharides to each other and bind mucopolysaccharides to proteins to form fibrous structures, thus increasing the elasticity and strength of connective tissue and maintaining structural integrity; Silicon participates in bone calcification and plays a role in the initial stage of calcification. Silicon in food can increase the speed of calcification, especially when calcium intake is low; About 21% of the amino acid in collagen is hydroxyproline. Prolyl hydroxylase hydroxylates proline. This enzyme needs silicon when it shows maximum activity; The analysis of collagen from different sources shows that silicon is one of the components of collagen^[12] 。

Reference intake: Since there is no experimental data on human silicon demand, it is difficult to propose a suitable daily silicon demand for human beings. It is estimated from animal experiments that if silicon is easily absorbed, the daily human silicon demand may be 2-5mg. However, most of the silicon in the diet is not easy to be absorbed, and the recommended intake is about 5-10mg per day. It can be considered that 20-50mg per day is appropriate^[12] 。

Overexpression: hypersilicosis. Focal glomerulonephritis was found in the population with high silicon diet, and individuals with significantly increased silicon content in renal tissue. It is also reported that a large amount of magnesium silicate (containing silicon antacid) may induce human urinary calculi^[12] 。

Silicosis, which can be caused by long-term inhalation of large amounts of silicon containing dust through the respiratory tract^[13] 。

Silicosis, also known as silicosis, is the most common type of pneumoconiosis. It is caused by long-term inhalation of large amounts of dust containing free silica, and is mainly a disease of extensive nodular fibrosis in the lung. Silicosis patients are prone to combine with other diseases, leading to deterioration of condition and even death, because the microvascular circulation of lung tissue is blocked due to extensive fibrous tissue hyperplasia in both lungs, and the resistance is reduced^[13] 。

Inadequate performance: The lack of silicon in the feed can slow the growth of animals. The lack of silicon can cause the hair and nails to break easily and the skin to lose luster. The results of animal experiments showed that silicon supplementation while feeding atherogenic beverages was beneficial to protecting the structure of the aorta of animals. In addition, it has been determined that the silicon content in the vascular wall is inversely proportional to the degree of atherosclerosis in humans and animals. In the population with two different long-term incidence rates of cardiovascular diseases, the silicon content in drinking water is also about twice as high, and the population with high silicon content in drinking water is less ill^[14] 。

Silicon is a very safe substance. It will not react with the immune system, will not be engulfed by cells, will not breed bacteria or react with chemical substances. At the same time, it can also have silica gel developed and produced for skin wounds, which can be used to protect wounds. It is a highly safe material and is licensed by health authorities in various countries.

Safety measures

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First aid measures

Inhalation: quickly leave the site to a place with fresh air. If you feel unwell, seek medical advice.

Skin contact: Take off contaminated clothes immediately, and wash skin thoroughly with soapy water and clean water. If you feel unwell, seek medical advice.

Eye contact: separate the eyelids and wash them with flowing water or normal saline. If you feel unwell, seek medical advice.

Ingestion: In case of discomfort. Get medical attention.

Advice for protecting the rescuer: transfer the patient to a safe place. Consult a doctor. Show this chemical safety data sheet to the doctor on site^[15] 。

Fire fighting measures

Extinguishing agent: use water mist, dry powder, foam or carbon dioxide extinguishing agent to extinguish the fire. Avoid using direct water to extinguish the fire. Direct water may cause splashing of flammable liquid and spread the fire.

Special danger: flammable, its powder can form explosive mixture when mixed with air. The dust reacts with flame or oxidant, which is of medium risk.

Precautions and protective measures for fire fighting: firefighters must wear air respirators, wear full body fire and gas protective clothing, and extinguish the fire upwind. Move the container from the fire site to an open place as far as possible. Spray water to keep the fire site container cool until the fire is extinguished. Prohibited water and carbon dioxide extinguishing agent: dry powder, dry sand^[15] 。

Leakage emergency treatment

Protective measures, protective equipment and emergency response procedures for operators:

Eliminate all ignition sources. Isolate the leakage contaminated area and restrict access. It is recommended that emergency personnel wear dust masks, anti-static clothing and protective gloves. Do not touch or cross the leakage. Cut off the leakage source as much as possible. Prevent leakage from entering water body, sewer, basement or confined space.

Environmental protection measures: collect leakage to avoid environmental pollution. Prevent leakage into sewers, surface water and groundwater.

Methods of receiving and removing leaked chemicals and disposal materials used:

Small amount of leakage: collect the leaked liquid in a sealable container as far as possible. Absorb with sand, activated carbon or other inert materials and transfer to a safe place. Do not flush into the sewer.

Large amount of leakage: build a dike or dig a pit to receive. Close the drainage pipe. Cover with foam to inhibit evaporation. Transfer to tank car or special collector with explosion-proof pump, recycle or transport to waste disposal site for disposal^[15] 。

Handling and storage

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Operation precautions

Open fire is prohibited. Prevent dust deposition, closed system, dust explosion electrical equipment and lighting. Prevent electrostatic charges from accumulating (e.g. by grounding).

The operators shall be specially trained and strictly abide by the operating procedures.

Operation and disposal shall be carried out in places with local ventilation or general ventilation facilities.

Avoid eye and skin contact and inhalation of vapor.

Keep away from kindling and heat sources, and smoking is strictly prohibited in the workplace.

Use explosion-proof ventilation systems and equipment.

If canning is required, the flow rate shall be controlled, and grounding device shall be provided to prevent electrostatic accumulation.

Avoid contact with forbidden compounds such as oxidants (see Part 10 for forbidden compounds).

Load and unload gently during transportation to prevent damage to packaging and containers.

Empty containers may leave harmful substances.

Wash your hands after use, and do not eat or drink in the workplace.

Fire fighting equipment and leakage emergency treatment equipment of corresponding types and quantities shall be provided^[15] 。

Precautions for storage

Store separately from substances with conflicting properties^[15] 。

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