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Synthetic diamonds are diamonds produced in technological processes, as opposed to natural diamonds, which are created in geological processes. Synthetic diamonds are also known as HPHT diamond or CVD diamond, HPHT and CVD which relate to the method of production, which are the synthesis of high pressure and high temperature (translation: high-pressure high-temperature), and chemical deposition steam (in English: chemical vapor deposition), respectively.
They have been documented numerous statements, between 1879 and 1928; every attempt has been carefully analyzed and none have been confirmed. In 1940, he began a systematic investigation in the United States, Sweden, and the Soviet Union to grow diamond processes using chemical vapor deposition and high pressure and high temperature. The first reproducible synthesis was reported around 1953. These two processes still dominate the production of diamond synthetic. A third method, known as detonation synthesis, has entered the diamond at the end of the 1990 market. During this process, are created diamond grain size on the nanometer scale, by detonating explosives containing carbon. It has been demonstrated in the laboratory fourth method: ultrasonic treating graphite with high power, but does not have commercial applications.
Synthetic diamond properties depend on the details of the manufacturing processes, and may be lower or higher than those of natural diamonds: hardness, thermal conductivity and electron mobility is higher in some synthetic diamonds (HPHT or CVD both). Consequently, synthetic diamonds are widely used in abrasives, cutting and grinding tools, and heatsinks. Applications are being developed electronic synthetic diamonds, including high power switches in power plants, field effect transistors for high frequency and LEDs. Synthetic diamond detectors of ultraviolet (UV) or high-energy particle research in high energy are used, and are commercially available. Due to its unique combination of thermal and chemical stability, low thermal expansion and high optical transparency in the range broad spectrum, synthetic diamonds are becoming the most popular material for the manufacture of optical windows in high-CO2 laser power, and gyrotrons.
Both CVD and HPHT diamonds can be cut into gems and can be produced various colors: clear, yellow, brown, blue, green, orange and white. The appearance of synthetic gems in the market has created significant concerns in the diamond trading business as a result of which have developed spectroscopic techniques and devices to distinguish between synthetic and natural diamonds.
After the discovery, in 1797, the diamond was pure carbon, many attempts have been made to convert various cheap forms of carbon, diamond. The earliest successes were reported by James Ballantyne Hannay in 1879 and by Henri Moissan in 1893. Their method involved heating coal at 3500 ° C in an oven with iron. Although Hannay used a flame heated tube Moissan applied his recently developed electric arc furnace, in which a was released arc between carbon bars in blocks cal. The molten iron was quickly cooled by immersion in water. The contraction generated by cooling, presumably producing the high pressure required to convert the graphite to diamond. Moissan published his work in a series of articles in the 1890s.
Many other scientists tried to replicate his experiments. Sir William Crookes in 1909 declared successful. Otto Ruff declared, in 1917, have produced diamonds up to 7 mm in diameter, but later retracted his statement. In 1926, Dr. Willard Hershey of McPherson College I replicated the experiments of Moissan and Ruff, producing a synthetic diamond; this specimen is on display at the McPherson Museum in Kansas. Despite the statements Moissan, Ruff, and Hershey, other experimenters have been unable to reproduce their synthesis.
The most definitive replication attempts were conducted by Sir Charles Algernon Parsons. Prominent scientist and engineer, known for his invention of the steam turbine, spent 30 years (1882-1922) and spent a considerable part of his fortune trying to reproduce the experiments of Moissan and Hannay, but also adapted processes on their own. Parsons was known for his painstakingly accurate approximation and methodical in storage Records. all results were preserved for later analysis by an independent team wrote a number of articles, some of the earliest on diamond HPHT-in which he claimed to have produced small diamonds However, in 1928. authorized the Dr. CH Desch to publish an article in which enunciated his belief that he had not been produced synthetic diamonds to date (including those of Moissan and others). He suggested that the Most diamonds that had occurred up to that point were like synthetic spinels.
In 1941, an agreement between the companies General Electric (GE), Norton and Carborundum was established to develop a synthesis of diamond. They were capable of heating carbon to about 3000 ° C under a pressure of 3.5 GPa for a few seconds. Shortly after the Second World War interrupted the project. It was resumed in 1951 in Schenectady Laboratories of General Electric, and a group of high-pressure diamond formed with FP Bundy and H. M. Strong. Howard Tracy Hall and others joined the project soon after.
The group made improvements in Schenectady anvils designed by Percy Bridgman, who received a Nobel Prize for his work in 1946. Bundy and Strong made the first improvements after Hall made other. Team G. E. presses employed tungsten carbide in a hydraulic press to compress a sample contained in a coal catlinite container. The team recorded the synthesis of diamond on one occasion, but the experiment could not be reproduced because of the uncertain conditions of synthesis.
Hall got his first successful commercial diamond synthesis on December 16, 1954, and this was announced on February 15, 1955. This accomplishment was achieved using a press of "belt", which is capable of producing pressures above 10 GPa and temperatures above 2000 ° C.
At the press of "belt" (see below) filling a container pyrophyllite graphite dissolved nickel, cobalt, or cast iron was introduced. These metals acted as a "solvent-catalyst" which both dissolved carbon as accelerating its conversion into diamond. The largest diamond got was 0.15 mm long, too small for jewelery and visually imperfect but usable as industrial abrasives. Hall’s collaborators were able to replicate their work, and the discovery was pubilcado in Nature. was the first person to grow a synthetic diamond with a reproducible, verifiable and well documented process. He left General Electric in 1955, and three years later he developed a new apparatus for the synthesis of diamond-a tetrahedral press with four anvils-to avoid violating its prior patent, he was still assigned to General Electric. Hall received the prize of the American Chemical Society for Creative Invention for his work on the synthesis of diamond.
Was achieved independent diamond synthesis on 16 February 1953 in Stockholm, Sweden for the Allmänna Elektriska Svenska Aktiebolaget (ASEA), a leading Swedish manufacturing companies. Beginning in 1949, ASEA hired a team of five scientists and engineers as part of a top secret project to produce diamond, codenamed QUINTUS. The team used an apparatus designed by Baltzar von Platen and Anders Kämpe. The pressure was maintained within the device to an estimated 8.4 GPa for one hour. Were produced few small diamonds, but not the size or gem quality.. Work was not reported until the 1980s During the 1980s, a new competitor emerged in Korea, a company called Iljin Diamond; was followed by hundreds of Chinese companies. Iljin Diamond argued that having the diamond synthesis in 1988 of improperly appropriating trade secrets of General Electric, through a previous Korean GE employee.
The first synthetic diamond crystals of gem quality were created in 1970 by General Electric, being published in 1971. Early successes used a pyrophyllite tube with thin pieces of diamond on both ends of the tube. The feedstock, graphite, stood in the center, and the solvent metal (nickel) between graphite and diamonds. The container is heated and the pressure increases to about 5.5 GPa. The crystals grow to once it flows from the center to the ends of the tube, and extending the length of the process produces larger crystals. Initially, a process of growing one week produced gem stone quality of about 5 mm (1 carat or 0.2 g), the process conditions have to be as stable as possible. The feed was replaced by graphite soon diamond grains, allowing better control of the final shape of the glass.
The first stones of gem quality were always one color from yellow to brown, due to nitrogen pollution. The inclusions were common, especially flattened, due to nickel. Removing all nitrogen from the process by the addition of aluminum or titanium produced "white" Colorless, stones and nitrogen removal and addition of boron resulted in blue. However, the nitrogen removal process slowed growth, and reduced the crystal quality, so the process was usually performed with nitrogen present.
Although GE stones and natural diamonds were chemically identical, their physical properties were not the same. Colorless stones produced strong fluorescence and phosphorescence under ultraviolet light of short wavelength, but were inert under long-wave UV. Among natural diamonds, only the rarer blue gems exhibited these properties. Unlike natural diamonds, all stones GE showed yellow fluorescence under X ray Diamond De Beers Research Laboratory has grown stones up to 25 carats, for research purposes. HPHT conditions remained stable for 6 weeks to grow high quality diamond of this size. For economic reasons, the growth of most synthetic diamonds are terminated when they reach a weight of 1 to 1.5 carat.
In the 1950s, research began in the Soviet Union and USA regarding diamond growth by pyrolysis of hydrocarbon gases to the relatively low temperature of 800 ° C. This low pressure process is known as chemical vapor deposition (CVD). William G. Eversole reported having the vapor deposition of diamond on diamond substrate in 1953 but was not reported until 1962. The deposition of diamond film was independently reproduced by Angus and his team in 1968 and Deryagin and Fedoseev in 1970. While Eversole and Angus used a single crystal diamond, big and expensive, as substrates, Deryagin and Fedoseev succeeded in making diamond films on diamond different materials (silicon and metals), which led to a massive research for cheap diamond coatings in the 1980s
There are several methods used to produce synthetic diamonds. The original method uses high pressure and high temperature (HPHT), and is still widely used due to its relatively low cost. The process involves large presses which can weigh hundreds of tons to produce a pressure of 5 GPa at 1500 ° C. The second method, using chemical vapor deposition (CVD), a plasma of carbon is created on a substrate on which is deposited carbon to atoms form diamond. Other methods include using explosives training (formation of detonation nanodiamonds) and sonication of graphite solutions.
In the HPHT method, there are three main press designs used to supply the pressure and temperature required to produce synthetic diamond: the belt press, the cubic press and the fractional area (or press BARS).
The original development of GE by Tracy Hall uses a belt press in which the upper and lower anvils providing pressure load to an inner cylindrical cell. This internal pressure is limited radially by a belt tensioning steel bands. The anvils also serve as electrodes for providing electrical power to heat the compressed cell. A variation of the belt press uses hydraulic pressure instead of cables steel, to limit internal pressure. The band presses are still used today, but they are a much larger scale than the original design.
The second type of press design is the cubic press. A press has six anvils cubic providing pressure simultaneously on all the faces of a cube-shaped volume. The first multi-press design was a tetrahedral anvil press with four anvils which converge in a volume in tetrahedral shape. The cubic press was established soon after increasing the volume under pressure. A cubic press is typically smaller than a press belt and can be achieved more quickly the pressure and temperature necessary to create synthetic diamond. However, the cubic presses can not be easily extended to larger volumes: the volume of pressure can be increased by the use of large anvils, but this also increases the amount of force necessary to achieve the anvils at the same pressure. An alternative is to decrease the surface area to volume ratio of the volume to pressure by using more anvils to converge to a platonic solid higher order, such as a dodecahedron. However, such a release would be complex and difficult to manufacture.
The BARS press is the most compact, efficient and economical of all diamond production presses. In the center of a bar device, cylindrical ceramic "capsule synthesis" of about 2 cm3 in size. The cell is placed in a bucket of pressure transmission of material such as ceramic pyrophyllite, which is pressed by inner anvils made of cemented carbide (eg tungsten carbide or hard alloy VK10). The octahedral cavity Outdoor pressed for 8 outdoor steel anvil. After assembly, the entire assembly is enclosed in a barrel type disk with a diameter of about 1 meter. The barrel is filled with oil, which pressurizes by heating, and the oil pressure is transferred to the plant cell. Synthesis capsule is heated by a coaxial graphite heater and the temperature is measured with a thermocouple.
The chemical vapor deposition is a method by which diamond is created from a mixture of hydrocarbon gases. Since the 1980s, this method has been the subject of intensive research worldwide. Whereas mass production of crystals of high quality diamond HPHT process make the most suitable choice for industrial applications, the flexibility and simplicity of configuration CVD explain the popularity of this method in research laboratories. The advantages of CVD diamond growth include the ability to grow diamond on large areas and on various substrates, and the precise control of chemical impurities and thus properties of the diamond produced. Unlike HPHT, CVD process requires high pressures, such as growth typically occurs at pressures below 27 kPa.
May form diamond nanocrystals (5 nm in diameter) by detonating explosives containing certain carbon and are deficient in oxygen (see Equations of Kamlet-Jacobs) in a metal chamber. These nanocrystals are known as "detonation nanodiamonds". During the explosion, the pressure and temperature in the chamber is high enough to convert the carbon into diamond explosives. Being immersed in the water chamber rapidly cooled after the explosion, and the conversion of diamond just produced more stable graphite stops. In a variation of this technique, a tube filled with graphite powder metal is placed in the detonation chamber. The explosion heats and compresses the graphite enough for conversion to diamond. The product is always rich in graphite forms of carbon and other non-diamond and requires a prolonged stay in nitric acid hot (about 1 day at 250 ° C) to dissolve them. recovered nanodiamond powder is mainly used in polishing applications. It occurs mainly in China, Russia and Belarus, and began to hit the market in large quantities in the early 2000s.
Can be synthesized diamond crystals micron size from a graphite suspension in an organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The performance of diamond is about 10% of the initial weight of graphite. The estimated cost of diamond produced by this method is comparable to the HPHT method; the crystalline perfection of the product is significantly worse in this method. This technique requires a relatively simple equipment and procedures, but has only been reported by two research groups, and has no industrial use since 2009. Numerous process parameters, such as the preparation of the initial graphite powder, choosing ultrasonic energy, the time of synthesis and the solvent, has not yet been optimized, leaving a window for the improvement of the efficiency and potential cost reduction of the Ultrasonic synthesis.