SILICON [Si]
Characteristics
An: 14 N: 14
Am: 28.0855 g/mol
Group No: 14
Group Name: Metalloids
Block: p-block Period: 3
State: solid at 298 K
Colour: dark grey with a bluish tinge
Classification: Semi-metallic
Boiling Point: 3173K (2900oC)
Melting Point: 1687K (1414oC)
Density: 2.33g/cm3
Discovery Information
Who: Jons Berzelius
When: 1823
Where: Sweden
Name Origin
Latin silex, or silicis (meaning what were more generally termed "the flints" or "hard rocks" during the Early Modern era where nowadays we would say "silica" or "silicates") Silicon" in different languages.
Sources
Silicon is the second most abundant element and comprises 25.7% of the earth’s crust (oxygen is first). Makes up major portion of clay, granite, feldspar, mica, asbestos, quartz (SiO2), and sand.
Primary producers are Austria, Italy, India, South Africa, Australia, Canada, the USA and Brazil. Every year around 5000 tons of electronics grade silicon is produced.
Abundance
Universe: 700 ppm (by weight)
Sun: 900 ppm (by weight)
Carbonaceous meteorite: 1.4 x 105 ppm
Earth’s Crust: 2.771 x 105 ppm
Seawater: Atlantic surface: 0.03 ppm, Atlantic deep: 0.82 ppm, Pacific surface: 0.03 ppm, Pacific deep: 4.09 ppm
Human: 260000 ppb by weight, 58000 ppb by atoms
Uses
Used in glass as silicon dioxide (SiO2). It is used as a semiconductor to make microchips for electronics (like your computer). Silicon is also used in solar cells, tools, cement, LCDs, grease and oils.
History
Silicon (Latin silex, silicis for flint, flint’s) was first identified by Antoine Lavoisier in 1787, and was later mistaken by Humphry Davy in 1800 for a compound. In 1811 Gay-Lussac and Thenard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. In 1824, Berzelius prepared amorphous silicon using approximately the same method as Lussac. Berzelius also purified the product by repeatedly washing it.
Notes
Silicon carbide (SiC) is one of the hardest substances known.
Hazards
Fine powder is highly flammable.
A serious lung disease known as silicosis often occurred in miners, stonecutters, and others who were engaged in work where siliceous dust was inhaled in great quantities.
Silicon Compounds
Molybdenum(IV) silicide MoSi2
Molybdenum disilicide heating elements can be used for temperatures up to 1800oC (2073 K), in electric furnaces used in laboratory and production environment in production of glass, steel, electronics, ceramics, and in heat treatment of materials. While the elements are brittle, they can operate at high power without aging, and their electrical resistivity does not increase with operation time.
Polydimethylsiloxane (CH3)3SiO[SiO(CH3)2]nSi(CH3)3
It is the primary component in Silly Putty. The rubbery, vinegary-smelling silicone caulks, adhesives, and aquarium sealants are also well-known. PDMS is also used as a component in silicone grease and other silicone based lubricants, as well as in defoaming agents, damping fluids, heat transfer fluids, cosmetics, hair conditioner and other applications. PDMS has also been used as a filler fluid in breast implants, although this practice has decreased somewhat, due to safety concerns. It continues to be used in knuckle replacement implants, with good results.
As a food additive, it has the E number E900 and is used as an anti-foaming agent and an anti-caking agent.
Platinum silicide PtSi
It is used in detectors for infrared astronomy.
Silicon-germanium SiGe
This semiconductor material is commonly used in the integrated circuit manufacturing industry.
Silane SiH4 [Irritant]
At room temperature, silane is a gas, and is pyrophoric - it undergoes spontaneous combustion in air, without the need for external ignition.
Several industrial and medical applications exist for silanes. For instance, silanes are used as coupling agents to adhere glass fibres to a polymer matrix, stabilizing the composite material. They can also be used to couple a bio-inert layer on a titanium implant. Other applications include water repellents, masonary protection, control of graffiti, applying polycrystalline silicon layers on silicon wafers when manufacturing semiconductors, and sealants.
Silicon carbide SiC
The word moissanite is a trade name given to silicon carbide for use in the gem business.
Silicon carbide is used for blue LEDs, ultrafast Schottky diodes, MESFETs and high temperature IGBTs and thyristors for high power switching. Due to its high thermal conductivity, SiC is also used as substrate for other semiconductor materials such as gallium nitride.
Silicon carbide’s hardness and rigidity make it a desirable mirror material for astronomical work, although they also make manufacturing and figuring such mirrors quite difficult.
Silicon-infiltrated carbon-carbon composite is used for high performance brake discs as it is able to withstand extreme temperatures. The silicon reacts with the graphite in the carbon-carbon composite to become silicon carbide. These discs are used on some sports cars.
Silicon dioxide (silica) SiO2
Silica is found in nature in several forms, including quartz and opal. Inexpensive soda-lime glass is the most common and typically found in drinking glasses, bottles, and windows. The ceramic re-entry heat protection tiles mounted on the bottom side of the Space Shuttles are made mostly of silica (see HRSI), as are the firebricks used in steel processing.
Silica, along with alumina (silica-alumina), forms a major part of the crystal lattice of clay minerals. These decompose on firing and form part of the microstructure of clay based ceramics such as earthenware, stoneware and porcelain.
Silica is also used as a food additive, primarily as a flow agent in powdered foods, or to absorb water.
Silicon nitride Si3N4
Silicon nitride is the main component in silicon nitride ceramics, which have relatively good shock resistance compared to other ceramics. Rollers made of silicon nitride ceramic are sometimes used in high-end skateboard bearings, due to the material’s shock and heat-resistant characteristics. Also used an ignition source for domestic gas appliances, Hot Surface Ignition.
Reactions of Silicon
Reactions with water
A surface layer of oxide makes silicon unreactive to water and steam.
Reactions with air
Due to a thin layer of oxide on a sample of silicon it will not react with oxygen below temperatures of 900oC, above this the reaction with oxygen gives silicon dioxide.
Si(s) + O2(g) --> SiO2(s)
At temperatures above 1400oC the silicon will react with nitrogen to give silicon nitrides.
2Si(s) + N2(g) --> 2SiN(s)
3Si(s) + 2N2(g) --> Si3N4(s)
Reactions with halogens
Silicon reacts vigorously with all the halogens to form tetrahalides, the reaction with fluorine takes place at room temperature, the others require heating over 300oC.
Si(s) + 2F2(g) --> SiF4(g)
Si(s) + 2Cl2(g) --> SiCl4(g)
Si(s) + 2Br2(l) --> SiBr4(l)
Si(s) + 2I2(l)--> SiI4(s)
Reactions with acids
Under normal conditions silicon does not react with most acids, but is dissolved by hydrofluoric acid.
Si(s) + 6HF(aq) --> [SiF6]2-(aq) + 2H+(aq) + 2H2(g)
Reactions with bases
Silicon is attacked by bases such as aqueous sodium hydroxide to give silicates.
Si(s) + 4NaOH(aq) --> [SiO4]4-(aq) + 4Na+(aq) + 2H2(g)
Occurrence of Silicon
Measured by mass, silicon makes up 25.7% of the Earth’s crust and is the second most abundant element on Earth, after oxygen. Pure silicon crystals are only occasionally found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as silica), and silicate.
Silica occurs in minerals consisting of (practically) pure silicon dioxide (SiO2) in different crystalline forms (quartz, chalcedony, opal). Sand, amethyst, agate, quartz, rock crystal, flint, jasper, and opal are some of the forms in which silicon dioxide appears. (They are known as "lithogenic", as opposed to "biogenic", silicas.)
Silicon also occurs as silicates (various minerals containing silicon, oxygen and one or another metal), for example feldspar. These minerals occur in clay, sand and various types of rock such as granite and sandstone. Asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.
Silicon is a principal component of aerolites, which are a class of meteoroids, and also is a component of tektites, which are a natural form of glass.
Isotopes of Silicon
28Si [14 neutrons]
Abundance: 92.23%
Stable with 14 neutrons
29Si [15 neutrons]
Abundance: 4.67%
Stable with 15 neutrons
30Si [16 neutrons]
Abundance: 3.1%
Stable with 16 neutrons
32Si [18 neutrons]
Abundance: synthetic
Half life: 132 years [ beta- ]
Decay Energy: 0.221 MeV
Decays to 32P.
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