High pressure
High pressure in science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

 and engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...

 is studying the effects of high pressure on materials and the design and construction of devices, such as a diamond anvil cell
Diamond anvil cell
A diamond anvil cell is a device used in scientific experiments. It allows compressing a small piece of material to extreme pressures, which can exceed 3,000,000 atmospheres ....

, which can create high pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

. By high pressure it is usually meant pressures of thousands (kilobar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

s) or millions (megabars) of times atmospheric pressure (about 1 bar).

Percy Williams Bridgman
Percy Williams Bridgman
Percy Williams Bridgman was an American physicist who won the 1946 Nobel Prize in Physics for his work on the physics of high pressures. He also wrote extensively on the scientific method and on other aspects of the philosophy of science.- Biography :Bridgman entered Harvard University in 1900,...

 received a Nobel prize for advancing this area of physics by several magnitudes of pressure (400Mpa to 40,000Mpa). The list of founding fathers of this field includes also the names of Harry George Drickamer
Harry George Drickamer
Prof. Harry George Drickamer , born Harold George Weidenthal, was a pioneer experimentalist in high-pressure studies of condensed matter. His work generally concerned understanding the electronic properties of matter....

, Tracey Hall, F.P. Bundy, L.F. Vereschagin, Sergey M. Stishov.

It was by applying high pressure as well as high temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 to carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 that man-made diamond
Synthetic diamond
Synthetic diamond is diamond produced in a technological process; as opposed to natural diamond, which is created in geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond, denoting the production method, High-Pressure High-Temperature synthesis and Chemical...

s were first produced as well as many other interesting discoveries. Almost any material when subjected to high pressure will compact itself into a denser form, for example, quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

, also called silica or silicon dioxide
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

 will first adopt a denser form known as coesite
Coesite[p] is a form of silicon dioxide SiO2 that is formed when very high pressure , and moderately high temperature , are applied to quartz. Coesite was first synthesized by Loring Coes, Jr., a chemist at the Norton Company, in 1953. In 1960, coesite was found by Edward C. T...

, then upon application of more temperature, form stishovite
Stishovite is an extremely hard, dense tetragonal form of silicon dioxide. It was long considered the hardest known oxide; however, boron suboxide has recently been discovered to be much harder...

. These two forms of silica were first discovered by high pressure experimenters, but then found in nature at the site of a meteor impact.

Chemical bonding is likely to change under high pressure, when the P*V term in the free energy becomes comparable to the energies of typical chemical bonds - i.e. at around 100 GPa. Among the most striking changes are metallization of oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 at 96 GPa (rendering oxygen a superconductor), and transition of sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 from a nearly-free-electron metal to a transparent insulator at ~200 GPa. At ultimately high compression, however, all materials will metallize.

High pressure experimentation has led to the discovery of the types of minerals which are believed to exist in the deep mantle of the Earth, such as perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...

 which is thought to make up half of the Earth's bulk, and post-perovskite
Post-perovskite is a high-pressure phase of magnesium silicate . It is composed of the prime oxide constituents of the Earth's rocky mantle , and its pressure and temperature for stability imply that it is likely to occur in portions of the lowermost few hundred km of Earth's mantle.The...

, which occurs at the core-mantle boundary and explains many anomalies inferred for that region.

Pressure "landmarks": pressure exerted by a fingernail scratching is ~0.6 GPa, typical pressures reached by large-volume presses are up to 30-40 GPa, pressures that can be generated inside diamond anvil cell
Diamond anvil cell
A diamond anvil cell is a device used in scientific experiments. It allows compressing a small piece of material to extreme pressures, which can exceed 3,000,000 atmospheres ....

s are ~320 GPa, pressure in the center of the Earth is 364 GPa, and highest pressures ever achieved in shock waves are over 100,000 GPa.

Further reading

  • The New Alchemists: Breaking Through the Barriers of High Pressure, Robert M. Hazen, Times Books, Random House, 1993, hardcover, 286 pages, ISBN 0-8129-2275-1
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