Synthetic diamond
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[[Image:Apollo cultured diamonds.jpg|thumb|A collection of colorless cultured diamonds grown by [[Apollo Diamond]], Inc. via [[Chemical vapor deposition of diamond|chemical vapour deposition]]]]
'''Synthetic diamond''' (also known variously as ''lab-created'', ''manufactured'', ''lab-grown'' or ''cultured diamond'') is a term used to describe [[diamond]] crystals produced by a [[technology|technological]] process, as opposed to natural diamond, which is produced by [[geology|geological]] processes.
Synthetic diamond is not the same as [[diamond-like carbon]], DLC, which is amorphous hard carbon, or [[diamond simulant]]s, which are made of other materials such as [[cubic zirconia]] or [[silicon carbide]]. The properties of synthetic diamond depend on the manufacturing process used to produce it, and can be inferior, similar or superior to those of natural diamond.<ref>H. Sumiya, ''Rev. Sci. Instrum.'' ''76'' (2005), p. 026112</ref>
Because it can be made for less than it costs to mine and process natural diamond, synthetic diamond is used in many industrial applications. Reduced costs and the ability to [[materials science|engineer]] its physical and electrical properties give synthetic diamond the potential to become a [[disruptive technology]] in many areas, such as electronics and medicine.
==History==
[[Image:Hershey Synthetic diamond set up.jpg|thumb|Experimental set-up of Williard Hershey]]
The idea of making less expensive, gem-quality diamonds synthetically is not a new one. [[H. G. Wells]] described the concept in his short story "The Diamond Maker," published in 1911 <ref name = diamondmaker>[http://www.gutenberg.org/etext/456 "The Diamond Maker", Project Gutenberg]</ref>. In ''Capital'' [[Karl Marx]] commented, "If we could succeed, at a small expenditure of labour, in converting carbon into diamonds, their value might fall below that of bricks".<ref name = marx>{{cite book | authorlink = Karl Marx | author = Karl Marx | title = Capital, Vol. 1 | year = 1867 | publisher = Wikisource | url = http://en.wikisource.org/wiki/Das_Kapital/Chapter_1 }}</ref>
After the 1797 discovery that diamond was pure carbon, many attempts were made to alter the cheaper forms of carbon — generally with little success. One of the early successes reported in the field was by [[Henri Moissan|Ferdinand Frédéric Henri Moissan]] in 1893. His method involved heating [[charcoal]] at up to 4000 °C with iron in a [[carbon]] crucible in an electric furnace, in which an electric arc was struck between carbon rods inside blocks of [[lime (mineral)|lime]]. The molten iron was then rapidly cooled by immersion in water. The contraction generated by the cooling supposedly produced the high pressure required to transform graphite into diamond. Moissan published his work in a series of articles in the 1890s.
Many other scientists tried to replicate his experiments. Sir [[William Crookes]] claimed success in 1909. Ruff claimed in 1917 to have reproduced diamonds up to 7 mm in diameter, but later retracted his claims. <ref name = nassau> {{cite book | last = Nassau | first = Kurt | title = Gems made by Man | publisher = Chilton Book Co. | year = 1980}}</ref> In 1926, Dr. Willard Hershey of [[McPherson College]] read journal articles about Moissan's and Ruff's experiments and replicated their work, producing a synthetic diamond. That diamond is on display today in Kansas at the [[McPherson Museum]]. <ref name = hershey> {{cite book | author= J. Willard Hershey Ph.D. | title = Book of Diamonds | publisher = Heathside Press, New York | year = 1940| url=http://www.farlang.com/diamonds/hershey-diamond-chapters/page_131}}</ref> Despite the claims of Moissan, Ruff, and Hershey, many other experimenters had enormous difficulty in creating the required temperatures and pressure with similar equipment, leading some to contend that the early successes were the result of seeding by good-willed co-workers. <ref>O'Donoghue, Michael (ed.) ''Gems'', 6th edition, Elsevier, 2006, ISBN 10: 0-75-065856-8. p. 473</ref>
The most definitive duplication attempts <ref name = nassau /> were performed by Sir [[Charles Algernon Parsons]]. He devoted 30 years and a considerable part of his fortune to reproduce many of the experiments of Moissan as well as those of Hannay but also adapted processes of his own. He wrote a number of articles — one of the earliest on high-pressure/high-temperature (HPHT) diamonds — in which he claimed to have produced small diamonds. <ref name = parsons> [http://www.farlang.com/diamonds-references See Synthetic Diamond Section, Parson's articles of 1893 and those of others] </ref>. However in 1928 he authorized C.H Desch to publish an article in which he stated his belief that no synthetic diamonds (including those of Moisan and others) had been produced up to that date. In fact he found that most diamonds produced so far were more likely than not synthetic [[Spinel]]. <ref name = nassau/>
===The GE diamond project===
In 1941 an agreement was made between [[General Electric]], Norton and Carborundum to further develop diamond synthesis. They were able to heat carbon to about 3000 °C (5432 °F) under a pressure of half a million psi, for a few seconds.<ref name = nassau /> The [[Second World War]] ended this project soon thereafter. It was resumed in 1951 at the Schenectady Laboratories of GE and a high pressure diamond group was formed with F.P. Bundy and H.M. Strong. Shortly afterwards [[Howard Tracy Hall|Tracy Hall]] and others joined it.
The group improved on the [[Diamond_anvil_cell|anvils]] designed by [[Percy Bridgman]], who received a [[Nobel prize]] for his work in 1946. Bundy and Strong made the first improvements and more were made later by Hall. The GE team used a [[tungsten carbide]] anvil within a hydraulic press to squeeze the carbonaceous sample held in a [[catlinite]] container, the finished grit being squeezed out of the container through a gasket. It was believed that on occasion a diamond was produced, but since experiments could not be reproduced, such claims could not be maintained. <ref name = nassau />
Hall achieved the first commercially successful synthesis of diamond on [[December 16]], [[1954]] (announced on February 15, 1955). His breakthrough was using an elegant "belt" press apparatus which raised the achievable pressure from 6 to 18 GPa and the temperature to 5000 °C, using a [[pyrophyllite]] container, and having the graphite dissolved within molten nickel, cobalt or iron, a "solvent-catalyst". The largest diamond he produced was 150 micrometres across, clearly unsuitable for jewelry but very useful in industrial abrasives.<ref name = nassau /> Hall was able to have co-workers replicate his work and the discovery was published in [[Nature (journal)|''Nature'']]. He was the first person to grow a synthetic diamond according to a reproducible, verifiable and witnessed process and received a gold medal of the [[American Chemical Society]] in 1972 for his work.<ref name = nassau/> Hall left GE in 1955, and three years later developed a completely independent apparatus for the synthesis of diamond, the tetrahedral press with four anvils, thus avoiding infringement of his previous patent, which was still assigned to GE.
=== Later developments ===
Another successful diamond synthesis was produced on [[February 16]], [[1953]] in [[Stockholm]], [[Sweden]] by the QUINTUS project of [[ASEA]] (Allemanna Svenska Elektriska Aktiebolaget), [[Sweden]]'s major electrical manufacturing company using a bulky split sphere apparatus designed by [[Baltzar von Platen (1898-1984)|Baltzar von Platen]] and the young engineer Anders Kämpe (1928–1984). Pressure was maintained within the device at an estimated [[high pressure|83,000 atmospheres]] (8.4 GPa) for an hour. A few small crystals were produced, but not of gem quality or size. The work was not reported until the 1980s.
During the 1980s a new competitor emerged in Korea named Iljin Diamond, followed later by hundreds of Chinese entrants. Iljin Diamond allegedly accomplished this by misappropriating trade secrets from GE via a Korean former GE employee in 1988.<ref>General Electric v. Sung, 843 F. Supp. 776</ref>
Synthetic gem-quality diamond crystals were first produced in 1970 (reported in 1971) again by GE. Large crystals need to grow very slowly under extremely tightly controlled conditions. The first successes used a pyrophyllite tube seeded at each end with thin pieces of diamond and with the graphite feed material placed in the centre, the metal solvent, nickel, was placed between the graphite and the seeds. The container was heated and the pressure raised to around 55,000 atmospheres. The crystals grow as they flow from the centre to the ends of the tube, the longer the process is extended the larger the crystals - initially a week-long growth process produced gem-quality stones of around 5 mm and one carat. The graphite feed was soon replaced by diamond grit, as there was almost no change in material volume so the process was easier to control.
The first gem-quality stones were predominantly cubic and octahedral in form and, due to contamination with nitrogen, always yellow to brown in color. Inclusions were common, especially "plate-like" ones from the nickel. Removing all nitrogen from the process by adding aluminium or titantium produced a colourless 'white' stone, while removing the nitrogen and adding [[boron]] produced a blue. However removing nitrogen slows the growth process and reduces the quality of the crystals, so the process is normally run with nitrogen present. In terms of physical properties the GE stones were not quite identical to natural stones. The colourless stones were semi-conductors and fluoresced and phosphoresced strongly under short-wave [[ultraviolet radiation]] but were inert under long-wave UV - in nature only blue stones should do this. All the GE stones also showed a strong yellow fluorescence under X-rays. De Beers Diamond Research Laboratory has since grown stones of up to 11 carats, but most stones are around 1 to 1.5 carats for economic reasons, especially with the spread of the Russian [[BARS (Diamonds)|BARS]] apparatus since the 1980s.
Following on from work by John Angus and Boris Spitsyn researchers at the National Institute for Research in Inorganic Materials in Tsukuba produced diamonds at less than one atmosphere of pressure and only 800 °C through [[chemical vapor deposition]] (CVD). The Japanese had begun their research in 1974 and reported their success in 1981.
== Properties ==
The gem diamond is just one of many different forms that diamond can take. Natural gem diamond is a single crystal diamond with low levels of impurities. This homogeneity is what allows it to be clear, while its material properties and hardness are what make it a popular gemstone. Most natural diamond removed from the earth's crust does not have the high purity or high [[crystallinity]] necessary to be a quality gemstone. Following are some important properties by which various types of diamond are described.
; Crystallinity: A mass of diamond may be one single, continuous crystal or it may be made of up many smaller crystals ("polycrystalline"). Single crystal diamond is typically used in gemstones, while polycrystalline diamond is commonly used in industrial applications such as mining and cutting tools. Within polycrystalline diamond the diamond is often described by the average size of the crystals that make it up, called the "grain size." Grain sizes range from hundreds of micrometers to nanometers, usually referred to as "microcrystalline" and "nanocrystalline" diamond, respectively.
; Hardness: A diamond's [[hardness]] can vary depending on its impurities and crystallinity. Nanocrystalline diamond produced through CVD diamond growth, for instance, can have a wide range of hardness from 30% to 75% of single crystal diamond, and the hardness can be controlled to be used in specific applications. Some single crystal diamonds grown through chemical vapor deposition have been shown to be harder than any known natural diamond.
; Impurities and inclusions: No crystal is absolutely pure. Any substance other than carbon found in a diamond is an impurity, and may also be called an inclusion, due to the way these impurities fall in the crystal lattice. While inclusions can be unwanted, they can also be introduced on purpose to control the properties of the diamond. For instance, while pure diamond is an electrical insulator, diamond with small amounts of boron added is an electrical conductor, possibly allowing it to be used in new technological applications.
Gem-quality diamonds grown in a lab can be chemically, physically and optically identical to naturally occurring ones although they can be distinguished by [[spectroscopy]] in [[infrared spectroscopy|infrared]], [[ultraviolet]], or [[X-ray spectroscopy|X-ray]] wavelengths. The DiamondView tester from [[De Beers]] uses UV [[fluorescence]] to detect trace impurities of [[nickel]] or other metals in HPHT diamonds, or [[hydrogen]] in some LP CVD diamonds.
==Manufacturing technologies==
There are several methods used to produce synthetic diamond. The original method is High Pressure High Temperature (HPHT) and is still the most widely used method because of its relative low cost. It uses large presses that can weigh a couple of hundred tons to produce a pressure of 5 GPa at 1,500 degrees Celsius to reproduce the conditions that create natural diamond inside the Earth. A second method, using chemical vapor deposition or CVD, was invented in the 1980s, and is basically a method creating a carbon [[plasma (physics)|plasma]] on top of a substrate onto which the carbon atoms deposit to form diamond. A recent method uses thermal decomposition of the preceramic polymer [[poly(hydridocarbyne)]] to produce [[Diamond-like carbon]] and hexagonal diamond ([[Lonsdaleite]]). Other methods are explosive formation ([[detonation nanodiamond]]) and ultrasound sonication of solutions of graphite.
===High pressure, high temperature ===
The GE method is called HPHT (High Pressure, High Temperature). There are two main press designs used to supply the pressure and temperature necessary to produce synthetic diamond. These basic designs are the belt press and the cubic press. There are a number of other designs, but only belt press and cubic press are used for industrial scale manufacturing.
The original GE invention by Tracy Hall, uses the belt press, wherein upper and lower anvils supply the pressure load and heating current to a cylindrical volume. This internal pressure is confined radially by a belt of pre-stressed steel bands. A variation of the belt press uses hydraulic pressure to confine the internal pressure, rather than steel belts. Belt presses are still used today by the major manufacturers at a much larger scale than the original designs.
The second type of press design is the cubic press. A cubic press has six anvils which provide pressure simultaneously onto all faces of a cube-shaped volume. The first multi-anvil press design was actually a tetrahedral press, using only four anvils to converge upon a tetrahedron-shaped volume. The cubic press was created shortly thereafter to increase the pressurized volume. A cubic press is typically smaller than a belt press and can achieve the pressure and temperature necessary to create synthetic diamond faster. However, cubic presses cannot be easily scaled up to larger volumes. To illustrate, one could increase the pressurized volume by either increasing the size of the anvils, thereby increasing by a great factor the amount of force needed on the anvils to achieve a similar pressurization, or by decreasing the surface area to volume ratio of the pressurized volume by using more anvils to converge upon a different [[platonic solid]] (such as a dodecahedron), but such a press would be unnecessarily complex and not easily manufacturable.
===Chemical vapor deposition ===
{{main|Chemical vapor deposition of diamond}}
Chemical vapor deposition of diamond is a method of growing diamond by creating the environment and circumstances necessary for carbon atoms in a gas to settle on a diamond substrate in diamond crystalline form. This method of diamond growth has been the subject of a great deal of research since the early 1980s, especially due to its potential applications in the cutting tool, semiconductor and diamond gem industries.
In their pioneering work in the area, the Japanese passed a mixture of carbon-containing gas (methane in their case) and hydrogen into a quartz tube at a pressure of 0.05 atmospheres. Using microwaves the mixture was heated to 800 °C, disassociating both the methane and hydrogen into elemental forms. The carbon is deposited on a substrate, the majority as graphite but a very small proportion as diamond crystal. The graphite is 'removed' by the hydrogen leaving a thin layer of diamond; initially the layer was around 25μm in thickness.
===Explosive detonation===
Diamond nanocrystals can be formed from the detonation of certain explosives, resulting in the formation of [[detonation nanodiamond]]. These nanodiamonds are only now beginning to reach the market in bulk quantities, principally from Russia and China.
===Ultrasound cavitation===
Diamond nanocrystals can be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The yield is approximately 10%. Cost of nanodiamonds so produced are estimated to be competitive with the HPHT process. <ref name="sonication">Khachatryan ''et al.'' (2008) Graphite-to-diamond transformation induced by ultrasonic cavitation. ''Diamond and Related Materials'' '''17'''(6), June, 931–936.</ref>
===Preceramic polymer===
Hexagonal (as opposed to 'cubic') diamond (also known as [[lonsdaleite]]) can be formed from thermal decomposition of the preceramic polymer [[poly(hydridocarbyne)]] under Argon at atmospheric pressure and temperatures starting at 110 C.
==Applications==
Given the extraordinary set of physical properties diamond exhibits, diamond has and could have a wide-ranging impact in many fields.
=== Machining and cutting tools ===
Diamonds have long been used in [[machine tool]]s, especially when machining non-ferrous alloys. While natural diamond is certainly still used for this, the amount of synthetic diamond is far greater. The most common usage of diamond in cutting tools is done by distributing micrometer-sized diamond grains in a metal matrix (usually cobalt), hardening it and then [[sintering]] it onto the tool. This is typically referred to in industry as poly-crystalline diamond (PCD). PCD tipped tools are often used in mining and in the automotive aluminium cutting industry.
Diamond tools have been developed for stone, construction, etc for easy cutting, demolition of structures<ref>[http://www.reliancediamondtools.com/products.htm Diamond tools manufactured using synthetic diamonds and metal matrix images, applications videos] </ref>
For the past fifteen years work has also been done in the hope of using CVD diamond growth to coat tools with diamond,<ref name="tools">Ahmed ''et al.'' (2003) Diamond films grown on cemented WC–Co dental burs using an improved CVD method. ''Diamond and Related Materials'' '''12'''(8), August, 1300–1306.</ref> and though the work still shows promise it has not significantly displaced traditional PCD tools.
=== Electronics ===
[[chemical vapor deposition|CVD]] diamond also has applications in electronics. Conductive diamond is a useful electrode under many circumstances.<ref name="electrode">M. Panizza and G. Cerisola (2005) Application of diamond electrodes to electrochemical processes. ''Electrochimica Acta'' '''51'''(2), October, 191–199.</ref> [[University of Wisconsin-Madison]] chemistry professor [[Robert Hamers]] developed photochemical methods for covalently linking [[DNA]] to the surface of polycrystalline diamond films produced through CVD. In addition, the diamonds can detect [[redox]] reactions that cannot ordinarily be studied and in some cases degrade redox-reactive organic contaminants in water supplies. Because diamond is almost completely chemically inert it can be used as an electrode under conditions that would destroy traditional materials. For such reasons waste water treatment of organic effluents,<ref name="orga">D. Gandini, E. Mahé, P.A. Michaud, W. Haenni, A. Perret, Ch. Comninellis (2000) Oxidation of carbonylic acids at boron-doped diamond electrodes for wastewater treatment. ''Journal of Applied Electrochemistry'' '''20''';1345.</ref> as well as production of strong oxidants, have been published.<ref name="oxid">P.A. Michaud, E. Mahé, W. Haenni, A. Perret, Ch. Comninellis (2000) Preparation of peroxodisulfuric acid using Boron-Doped Diamond thin film electrodes. ''Electrochemical and Solid-State Letters'' '''3'''(2), Letters online.</ref> A number of companies produce diamond electrodes.
Diamond shows great promise as a potential [[semiconductor detector|radiation detection device]]. Diamond has a similar density to that of soft tissue, is radiation hard and has a wide bandgap. It is employed in applications such as the BABAR detector at Stanford.<ref name="radiation">M. Bucciolini (2005) Diamond dosimetry: Outcomes of the CANDIDO and CONRADINFN projects. ''Nuclear Instruments and Methods in Physics Research A'' 552, 189–196.</ref>
Diamond also has potential uses as a [[semiconductor]].<ref name="semi">A. Denisenko and E. Kohn (2005) Diamond power devices. Concepts and limits. ''Diamond and Related Materials'' '''14('''3-7), March-July, 491–498.</ref> This is because the diamonds can be "[[Doping (semiconductors)|doped]]" with impurities like [[boron]] and [[phosphorus]]. Since these elements contain one more or one less valence [[electron]] than carbon, they turn the diamonds into p-type or [[n-type semiconductor]]s. Diamond transistors are functional to temperatures many times that of silicon and are resistant to chemical and radioactive damage. While no diamond transistors have yet been successfully integrated into commercial electronics, they show promise for use in exceptionally high power situations and hostile environments.
CVD diamond growth has also been used in conjunction with lithographic techniques to encase microcircuits inside diamond. Researchers at [[Lawrence Livermore National Laboratory]] and the [[University of Alabama at Birmingham]] use this process to create designer diamond anvils as a novel probe for measuring electric and magnetic properties of materials at ultra high pressures using a [[Diamond Anvil Cell]].<ref name="designerdiamond">D.D. Jackson and C. Aracne-Ruddle and V. Malba and S.T. Weir and S.A. Catledge and Y.K. Vohra, Rev. Sci. Instrum., 74, 2467-2471 (2003)</ref>
HPHT "type IIa" diamonds are, as of 2007, approaching the very high purity and crystallographic structure perfection required to replace silicon in applications like X-ray tomographic imaging at [[synchrotron]]s;<ref>{{cite web | author=J.Heartwig et al. | title=Diamonds for Modern Synchrotron Radiation Sources | url=http://www.esrf.eu/UsersAndScience/Publications/Highlights/2005/Imaging/XIO5}}</ref> they will be able to sustain the increased intensities of next generation light sources.<ref>{{cite web | title=Diamond Monochromator for High Heat Flux Synchrotron X-ray Beams | author=A. M. Khounsary et al | url=http://www.aps.anl.gov/Facility/Technical_Publications/lsnotes/ls215/ls215.html}}</ref>
== Gemstones ==
Several companies currently produce gems made through HPHT technology. They are grown in split sphere high-pressure, high-temperature (HPHT) crystal growth chambers that resemble washing machines. The device bathes a tiny sliver of natural diamond in molten carbon at 1500 °C and 58,000 atm (5.9 GPa). This produces a rough diamond which can be cut down to a polished size close to half its original carat weight. [[D.NEA]], formerly Adia Diamonds, produces diamonds in various shades of yellow and orange as well as blue and white (colorless). The blue color comes from doping the diamond with boron, rather than nitrogen, during the growth process. White diamonds must be grown in an environment free of nitrogen and boron, which makes them very difficult to produce. Yellow diamonds are more profitable because they can be made more quickly and cost less to manufacture than blue or colorless diamonds. The largest synthetic diamond crystal grown to date via this method was a 34-carat yellow stone{{Fact|date=January 2008}}. [[Apollo Diamond]] is a company that currently produces gem diamond through chemical vapor deposition and sells clear diamond gemstones.
The mined diamond industry is evaluating marketing and distribution countermeasures to these less expensive alternatives. The three largest distributors have made public statements about selling their diamonds with full disclosure and have implemented measures to [[laser]]-inscribe serial numbers on their gemstones.<ref>{{cite news
| last =Yarnell
| first =Amanda
| title =The many facets of man-made diamonds
| work =Chemical and Engineering News
| pages =26-31
| publisher =American Chemical Society
| date =February 2, 2004
| url =http://pubs.acs.org/cen/coverstory/8205/8205diamonds.html
| accessdate = 2007-10-19 }}</ref>
[[LifeGem]] is a company offering to synthesize diamonds from the carbonized remains of people or pets.
== See also ==
* [[Diamond simulant]]
* [[Moissanite]]
* [[poly(hydridocarbyne)]]
== Notes ==
{{refs|2}}
== Further reading ==
* {{ cite book | title = The New Alchemists | subtitle = Breaking Through the Barriers of High Pressure | first = Robert M | last = Hazen | publisher = Times Books | location = Random House, New York | year = 1992 | format = hardcover | pages = 286 pages | id = ISBN 0812922751 }}
==External links==
{{wikisourcepar|Littell's Living Age/Volume 144/Issue 1859/The Asserted Artificial Production of the Diamond|a letter refuting an early attempt to create a synthetic diamond.}}
* Davis, J. (2003). [http://www.wired.com/wired/archive/11.09/diamond.html The New Diamond Age] Wired Magazine, Issue 11.09 (about CVD diamond growth)
* Yarnell, A. (2004). [http://pubs.acs.org/cen/coverstory/8205/8205diamonds.html The Many Facets of Man-Made Diamonds]. Chemical and Engineering News 82 (5), 26-31.
* Hall, H. T. (1961). [http://htracyhall.org/pdf/19610151.pdf The Synthesis of Diamond] Journal of Chemical Education, 38, 484
* [http://carnegieinstitution.org/raining_gems.html Carnegie Institution's Geophysical Laboratory]
* {{ cite web | url = http://www.llnl.gov/str/December04/Weir.html | title = Putting the Squeeze on Materials }}
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