Silicon
| Topics: |
Geology (main)
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Silicon is the second most common element in the Earth's crust, comprising 25.7% of the Earth’s crust by weight. It was discovered in 1824 by the Swedish chemist Jons Jakob Berzelius. It is shiny, dark gray with a tint of blue. Silicon, atomic number of 14, is a semi-metallic or metalloid, because it has several of the metallic characteristics. Silicon is never found in its natural state, but rather in combination with oxygen as a silicate ion (SiO4) in silica-rich rocks such as obsidian, granite, diorite, and sandstone. Feldspar and quartz are the most significant silicate minerals. Silicon alloys with a variety of metals, including iron, aluminum, copper, nickel, manganese and ferrochromium.
Contents
Background
Silica is processed into two intermediate products- silicon and ferrosilicon. Silicon is known in the ferroalloy and chemical industries as “silicon metal.” The ultra pure form of silicon (>99.99% Si) is distinguished from silicon metal by the term “semiconductor-grade silicon.” The terms “silicon metal” and “silicon” are used interchangeably.
Silicon is used in ceramics and in making glass. Ferrosilicon is crushed into a variety of forms and sold as bulk metal. Depending on its intended use, it can be mixed with aluminum and calcium. It is a very heavy alloy. When it comes into contact with moist air or water, an explosive chemical reaction occurs in which hydrogen is released. Consequently there are very strict laws about the shipping of ferrosilicon; it must be kept perfectly clean and dry.
Silicon is considered a semiconductor. This means that it conducts electricity, but not as well as a metal such as copper or silver. This physical property makes silicon an important commodity in the computer manufacturing business.
Ferrosilicon accounts for 53% of the annual silicon consumption in the United States; pure silicon accounts for the remaining 47%.
Silica is in human connective tissues, bones, teeth, skin, eyes, glands and organs. It is a major constituent of collagen which helps keep our skin elastic, and it helps calcium in maintaining bone strength. Silica dust in mines has caused silicosis or a lung disease in miners. Wetting the area being mined and application of good ventilation has reduced the danger of lung disease. Some organisms like sponges and some plants use silicon to create structural support.
Name
| Previous Element: Aluminum Next Element: Phosphorus |
| |
| Physical Properties | ||
|---|---|---|
| Color | gray-black | |
| Phase at Room Temp. | solid | |
| Density (g/cm3) | 2.336 | |
| Hardness (Mohs) | 7 | |
|
Melting Point (K) |
1683.2 | |
|
Boiling Point (K) |
3553 | |
| Heat of Fusion (kJ/mol) | 39.6 | |
| Heat of Vaporization (kJ/mol) | 383 | |
| Heat of Atomization (kJ/mol) | 452 | |
| Thermal Conductivity (J/m sec K) | 149 | |
| Electrical Conductivity (1/mohm cm) | 0.012 | |
| Source | Quartz | |
| Atomic Properties | ||
| Electron Configuration | [Ne]3s23p2 | |
|
Number of Isotopes |
21 (3 natural) | |
| Electron Affinity (kJ/mol) | 133.6 | |
| First Ionization Energy (kJ/mol) | 786.4 | |
| Second Ionization Energy (kJ/mol) | 1577 | |
| Third Ionization Energy (kJ/mol) | 3231.5 | |
| Electronegativity | 1.9 | |
| Polarizability (Å3) | 5.4 | |
| Atomic Weight | 28.086 | |
| Atomic Volume (cm3/mol) | 12 | |
| Ionic Radius2- (pm) | --- | |
| Ionic Radius1- (pm) | --- | |
| Atomic Radius (pm) | 117.6 | |
| Ionic Radius1+ (pm) | --- | |
| Ionic Radius2+ (pm) | --- | |
| Ionic Radius3+ (pm) | --- | |
| Common Oxidation Numbers | -4, +4 | |
| Other Oxid. Numbers | -3, -2, -1, +1, +2, +3 | |
| Abundance | ||
| In Earth's Crust (mg/kg) | 2.82×105 | |
| In Earth's Ocean (mg/L) | 2.20×101 | |
| In Human Body (%) | --- | |
| Regulatory / Health | ||
| CAS Number | 7440-21-3 | |
| OSHA Permissible Exposure Limit (PEL) | TWA: 15mg/m3 total particulate 5mg/m3 respirable particulate | |
| OSHA PEL Vacated 1989 | TWA: 10mg/m3 total particulate 5mg/m3 respirable particulate | |
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NIOSH Recommended Exposure Limit (REL) |
TWA: 10mg/m3 total particulate 5mg/m3 respirable particulate | |
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Sources: |
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The name silicon comes from the Latin word silicis which means flint.
Sources
Silicon compounds are the most significant component of the Earth’s crust. Silicon is recovered from an abundant resource: sand. Most pure sand is quartz, silicon dioxide (SiO2). Since sand is plentiful, easy to mine and relatively easy to process, it is the primary ore source of silicon. Some silicon is also retrieved from two other silicate minerals, talc and mica. The metamorphic rock, quartzite, is another source (quartzite is metamorphosed sandstone). All combined, world resources of silicon are plentiful and will supply demand for many decades to come.
The United States has plentiful sand, quartzite, talc and mica resources. The majority of the silica produced in the U.S. is produced East of the Mississippi River and in the Northwest. The U.S. also imports silicon from Norway, Russia, Brazil, Canada, and from a number of other countries.
Uses
Ferrosilicon alloys are used to improve the strength and quality of iron and steel products. Tools, for instance, are made of steel and ferrosilicon.
In addition to tool steels, an example of “alloy steels,” ferrosilicon is used in the manufacture of stainless steels, carbon steels, and other alloy steels (e.g., high-strength, low-alloy steels, electrical steels, and full-alloy steels).
An alloy steel refers to all finished steels other than stainless and carbon steels. Stainless steels are used when superior corrosion resistance, hygiene, aesthetic, and wear-resistance qualities are needed.
Carbon steels are used extensively in suspension bridges and other structural support material, and in automotive bodies, to name a few. Silicon is also added to aluminum to create a stronger alloy. The largest consumers of silicon metal are the aluminum and chemical industries.
Silicon is used in the aluminum industry to improve castability and weldability, not to add strength. Silicon-aluminum alloys tend to have relatively low strength and ductility, so other metals, especially Magnesium and copper, are often added to improve strength.
In the chemicals industry, silicon metal is the starting point for the production of silianes, silicones, fumed silica, and semiconductor-grade silicon. Silanes are the used to make silicone resins, lubricants, anti-foaming agents, and water-repellent compounds. Silicones are used as lubricants, hydraulic fluids, electrical insulators, and moisture-proof treatments.
Semiconductor-grade silicon is used in the manufacture of silicon chips and solar cells. Fumed silica is used as a filler in the cement and refractory materials industries, as well as in heat insulation and filling material for synthetic rubbers, polymers and grouts.
Other silicon materials are used in the production of advanced ceramic materials, including silicon carbide, silicon nitride, and sialons. Silicon carbide is also used as an abrasive material, a refractory agent, and in steel manufacturing.
Substitutes and Alternative Sources
There are relatively few options to replace silicon in its applications. Germanium and gallium arsenide can be used as semiconductors in place of silicon. In some applications, a small number of metal alloys, such as silicomanganese and aluminum, can substitute for ferrosilicon.
Further Reading
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
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