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Conductive diamond: synthesis, properties, and electrochemical applications. You have access to this article. Please wait while we load your content Something went wrong. Try again? Cited by. Back to tab navigation Download options Please wait Article type: Review Article. DOI: Download Citation: Chem. Conductive diamond: synthesis, properties, and electrochemical applications N. Yang, S. Yu, J. Macpherson, Y. Einaga, H. Zhao, G. Swain and X. Jiang, Chem. The graphite feed was soon replaced by diamond grit because that allowed much better control of the shape of the final crystal.
The first gem-quality stones were always yellow to brown in color because of contamination with nitrogen.
Inclusions were common, especially "plate-like" ones from the nickel. Removing all nitrogen from the process by adding aluminium or titanium produced colorless "white" stones, and removing the nitrogen and adding boron produced blue ones. Although the GE stones and natural diamonds were chemically identical, their physical properties were not the same. The colorless stones produced strong fluorescence and phosphorescence under short-wavelength ultraviolet light, but were inert under long-wave UV.
Among natural diamonds, only the rarer blue gems exhibit these properties. Unlike natural diamonds, all the GE stones showed strong yellow fluorescence under X-rays. Stable HPHT conditions were kept for six weeks to grow high-quality diamonds of this size. This low-pressure process is known as chemical vapor deposition CVD. William G. Eversole reportedly achieved vapor deposition of diamond over diamond substrate in , but it was not reported until From reports emerged of a rise in undisclosed synthetic melee diamonds small round diamonds typically used to frame a central diamond or embellish a band  being found in set jewelry and within diamond parcels sold in the trade.
However, international laboratories are now beginning to tackle the issue head-on, with significant improvements in synthetic melee identification being made. There are several methods used to produce synthetic diamonds. The original method uses high pressure and high temperature HPHT and is still widely used because of its relatively low cost. The second method, using chemical vapor deposition CVD , creates a carbon plasma over a substrate onto which the carbon atoms deposit to form diamond. Other methods include explosive formation forming detonation nanodiamonds and sonication of graphite solutions.
In the HPHT method, there are three main press designs used to supply the pressure and temperature necessary to produce synthetic diamond: the belt press, the cubic press and the split-sphere BARS press. Diamond seeds are placed at the bottom of the press. The molten metal dissolves the high purity carbon source, which is then transported to the small diamond seeds and precipitates , forming a large synthetic diamond.
Nano- and micro-crystalline diamond films and powders. - Free Online Library
The original GE invention by Tracy Hall uses the belt press wherein the upper and lower anvils supply the pressure load to a cylindrical inner cell. This internal pressure is confined radially by a belt of pre-stressed steel bands. The anvils also serve as electrodes providing electric current to the compressed cell. A variation of the belt press uses hydraulic pressure, rather than steel belts, to confine the internal pressure.
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. A cubic press is typically smaller than a belt press and can more rapidly achieve the pressure and temperature necessary to create synthetic diamond. However, cubic presses cannot be easily scaled up to larger volumes: the pressurized volume can be increased by using larger anvils, but this also increases the amount of force needed on the anvils to achieve the same pressure. An alternative is to decrease the surface area to volume ratio of the pressurized volume, by using more anvils to converge upon a higher-order platonic solid , such as a dodecahedron.
However, such a press would be complex and difficult to manufacture. The BARS apparatus is claimed to be the most compact, efficient, and economical of all the diamond-producing presses. The cell is placed into a cube of pressure-transmitting material, such as pyrophyllite ceramics, which is pressed by inner anvils made from cemented carbide e. After mounting, the whole assembly is locked in a disc-type barrel with a diameter about 1 meter. The barrel is filled with oil, which pressurizes upon heating, and the oil pressure is transferred to the central cell.
The synthesis capsule is heated up by a coaxial graphite heater and the temperature is measured with a thermocouple. Chemical vapor deposition is a method by which diamond can be grown from a hydrocarbon gas mixture. Since the early s, this method has been the subject of intensive worldwide research.
Whereas the mass-production of high-quality diamond crystals make the HPHT process the more suitable choice for industrial applications, the flexibility and simplicity of CVD setups explain the popularity of CVD growth in laboratory research. The advantages of CVD diamond growth include the ability to grow diamond over large areas and on various substrates, and the fine control over the chemical impurities and thus properties of the diamond produced. The CVD growth involves substrate preparation, feeding varying amounts of gases into a chamber and energizing them.
The gases always include a carbon source, typically methane , and hydrogen with a typical ratio of Hydrogen is essential because it selectively etches off non-diamond carbon. The gases are ionized into chemically active radicals in the growth chamber using microwave power, a hot filament , an arc discharge , a welding torch , a laser , an electron beam , or other means. During the growth, the chamber materials are etched off by the plasma and can incorporate into the growing diamond. In particular, CVD diamond is often contaminated by silicon originating from the silica windows of the growth chamber or from the silicon substrate.
Boron-containing species in the chamber, even at very low trace levels, also make it unsuitable for the growth of pure diamond. These nanocrystals are called " detonation nanodiamonds ". During the explosion, the pressure and temperature in the chamber become high enough to convert the carbon of the explosives into diamond. Being immersed in water, the chamber cools rapidly after the explosion, suppressing conversion of newly produced diamond into more stable graphite.
The explosion heats and compresses the graphite to an extent sufficient for its conversion into diamond. It is mainly produced in China, Russia and Belarus and started reaching the market in bulk quantities by the early s. Micron -sized diamond crystals can be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation.
A planar refractive X-ray lens made of nano-crystalline diamond
The estimated cost of diamond produced by this method is comparable to that of the HPHT method; the crystalline perfection of the product is significantly worse for the ultrasonic synthesis. This technique requires relatively simple equipment and procedures, but it has only been reported by two research groups, and has no industrial use as of [update].
Numerous process parameters, such as preparation of the initial graphite powder, the choice of ultrasonic power, synthesis time and the solvent, are not yet optimized, leaving a window for potential improvement of the efficiency and reduction of the cost of the ultrasonic synthesis. Traditionally, the absence of crystal flaws is considered to be the most important quality of a diamond.
Purity and high crystalline perfection make diamonds transparent and clear, whereas its hardness, optical dispersion luster , and chemical stability combined with marketing , make it a popular gemstone. High thermal conductivity is also important for technical applications. Whereas high optical dispersion is an intrinsic property of all diamonds, their other properties vary depending on how the diamond was created. Diamond can be one single, continuous crystal or it can be made up of many smaller crystals polycrystal.
Large, clear and transparent single-crystal diamonds are typically used as gemstones. Polycrystalline diamond PCD consists of numerous small grains, which are easily seen by the naked eye through strong light absorption and scattering; it is unsuitable for gems and is used for industrial applications such as mining and cutting tools. Polycrystalline diamond is often described by the average size or grain size of the crystals that make it up.
Grain sizes range from nanometers to hundreds of micrometers , usually referred to as "nanocrystalline" and "microcrystalline" diamond, respectively. Synthetic diamond is the hardest known material,  where hardness is defined as resistance to indentation. The hardness of synthetic diamond depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the  direction along the longest diagonal of the cubic diamond lattice.
Some synthetic single-crystal diamonds and HPHT nanocrystalline diamonds see hyperdiamond are harder than any known natural diamond. Every diamond contains atoms other than carbon in concentrations detectable by analytical techniques. Those atoms can aggregate into macroscopic phases called inclusions. Impurities are generally avoided, but can be introduced intentionally as a way to control certain properties of the diamond. Growth processes of synthetic diamond, using solvent-catalysts, generally lead to formation of a number of impurity-related complex centers, involving transition metal atoms such as nickel, cobalt or iron , which affect the electronic properties of the material.
For instance, pure diamond is an electrical insulator, but diamond with boron added is an electrical conductor and, in some cases, a superconductor ,  allowing it to be used in electronic applications. Nitrogen impurities hinder movement of lattice dislocations defects within the crystal structure and put the lattice under compressive stress , thereby increasing hardness and toughness.
Unlike most electrical insulators, pure diamond is an excellent conductor of heat because of the strong covalent bonding within the crystal. The thermal conductivity of pure diamond is the highest of any known solid. Single crystals of synthetic diamond enriched in 12 C Natural diamond's conductivity is reduced by 1.
Diamond's thermal conductivity is made use of by jewelers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2—3 seconds.
Most industrial applications of synthetic diamond have long been associated with their hardness; this property makes diamond the ideal material for machine tools and cutting tools. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial applications of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. While natural diamond is also used for these purposes, synthetic HPHT diamond is more popular, mostly because of better reproducibility of its mechanical properties.
Diamond is not suitable for machining ferrous alloys at high speeds, as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools compared to alternatives. The usual form of diamond in cutting tools is micron-sized grains dispersed in a metal matrix usually cobalt sintered onto the tool. This is typically referred to in industry as polycrystalline diamond PCD. PCD-tipped tools can be found in mining and cutting applications.
For the past fifteen years, work has been done to coat metallic tools with CVD diamond, and though the work shows promise, it has not significantly replaced traditional PCD tools. Most materials with high thermal conductivity are also electrically conductive, such as metals. In contrast, pure synthetic diamond has high thermal conductivity, but negligible electrical conductivity.
This combination is invaluable for electronics where diamond is used as a heat sink for high-power laser diodes , laser arrays and high-power transistors. Efficient heat dissipation prolongs the lifetime of those electronic devices, and the devices' high replacement costs justify the use of efficient, though relatively expensive, diamond heat sinks. Diamond is hard, chemically inert, and has high thermal conductivity and a low coefficient of thermal expansion.
These properties make diamond superior to any other existing window material used for transmitting infrared and microwave radiation. Therefore, synthetic diamond is starting to replace zinc selenide as the output window of high-power CO 2 lasers  and gyrotrons. Synthetic diamond has potential uses as a semiconductor ,  because it can be doped with impurities like boron and phosphorus.
Since these elements contain one more or one less valence electron than carbon, they turn synthetic diamond into p-type or n-type semiconductor. Combined with the high mechanical stability of diamond, those properties are being used in prototype high-power switches for power stations. Synthetic diamond transistors have been produced in the laboratory. They remain functional at much higher temperatures than silicon devices, and are resistant to chemical and radiation damage. While no diamond transistors have yet been successfully integrated into commercial electronics, they are promising for use in exceptionally high-power situations and hostile non-oxidizing environments.
Synthetic diamond is already used as radiation detection device. It is radiation hard and has a wide bandgap of 5. Diamond is also distinguished from most other semiconductors by the lack of a stable native oxide. This makes it difficult to fabricate surface MOS devices, but it does create the potential for UV radiation to gain access to the active semiconductor without absorption in a surface layer.
Conductive CVD diamond is a useful electrode under many circumstances. Such DNA modified films can be used for detecting various biomolecules , which would interact with DNA thereby changing electrical conductivity of the diamond film. Because diamond is mechanically and chemically stable, it can be used as an electrode under conditions that would destroy traditional materials. As an electrode, synthetic diamond can be used in waste water treatment of organic effluents  and the production of strong oxidants. The yellow color comes from nitrogen impurities in the manufacturing process, while the blue color comes from boron.
Gem-quality diamonds grown in a lab can be chemically, physically and optically identical to naturally occurring ones. The mined diamond industry has undertaken legal, marketing and distribution countermeasures to protect its market from the emerging presence of synthetic diamonds. At least one maker of laboratory-grown diamonds has made public statements about being "committed to disclosure" of the nature of its diamonds, and laser -inscribed serial numbers on all of its gemstones. The faceted jewel was cut from a Traditional diamond mining has led to human-rights abuses in Africa and elsewhere.
The Hollywood movie Blood Diamond helped to publicize the problem. Consumer demand for synthetic diamonds has been increasing, albeit from a small base, as customers look for stones which are ethically sound, and are cheaper. Around , the price of synthetic diamond gemstones e. In May , the large worldwide diamond company De Beers announced that they would introduce a new jewelry brand called "Lightbox" that features synthetic diamonds. In July , the U.
Federal Trade Commission approved a substantial revision to its Jewelry Guides, with changes that impose new rules on how the trade can describe diamonds and diamond simulants. The revised guide further states that "If a marketer uses 'synthetic' to imply that a competitor's lab-grown diamond is not an actual diamond, The De Beers Lightbox brand entered the market starting in September De Beers had previously limited its synthetic diamond production to industrial applications.
The website's FAQ page says the lab-grown diamonds are "neither as valuable or precious" as natural stones. From Wikipedia, the free encyclopedia. This article has multiple issues. Please help improve it or discuss these issues on the talk page. Learn how and when to remove these template messages. This article relies too much on references to primary sources. Please improve this by adding secondary or tertiary sources. June Learn how and when to remove this template message.
This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. Diamond produced in an artificial process. This section relies too much on references to primary sources. Please improve this section by adding secondary or tertiary sources.
Main article: Detonation nanodiamond. Main article: Crystallographic defects in diamond. Main article: Diamond gemstone. Federal Trade Commission, July 21, Resource Investor. Archived from the original on January 28, Retrieved February 4, Philosophical Transactions of the Royal Society of London. With the Memoirs of Mathematics and Physics , part 2, — Gannal, who communicated some investigations into the action of phosphorus placed in contact with pure carbon disulfide, and into the product of his experiments, which have presented properties similar to those of particles of diamond.
Arago communique une note de M. Arago communicated a note from Mr.
Cagniard de Latour, in which this physicist states that he has, on his part, succeeded in making carbon crystallize by methods different from those of Mr. Gannal, and that a sealed packet which he deposited with the Secretary in contains the details of his initial procedures. Arago announced that he knew another person who had arrived at similar results, and Mr.
Gay-Lussac announced that Mr. Ganal had spoken to him eight years ago about his attempts.
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Cagniard de Latour. Thenard gave a reading of the minutes of experiments made on November 26, on the powder presented as artificial diamond by Mr. Comptes Rendus. London and New York's Harper Brothers. Gems made by Man. Chilton Book Co.
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