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Synthetic diamond PCD (Popular Science)


Known as the "diamond" diamond is a diamond, we often say, it is a mineral consisting of pure carbon, is the hardest substance in nature. Since the 18th century confirmed the diamond is composed of pure carbon later, people started the research on synthetic diamond, just in the 20th century 50s progression through the study of high-pressure and high pressure experimental technique to get real success and rapid development, artificial diamond is a kind of widely used in various industries, the technology industry.

The difference with natural diamond

Diamond, jewelry noble, it clear transparent, exudes a cool noble glory, quite "the silt but don't dye" temperament. Diamond also known as diamond, because it is the nature of the extremely hard material, Mohs hardness of 10, 15 new Mohs hardness, microhardness 10000kg/mm2, microhardness than quartz high 1000 times, than corundum high 150 times. It formed and found is not easy, it is carbon under the special conditions of the deep earth high temperature and pressure after "penance" hundreds of millions of years of transformation, due to the movement of the earth's crust, they from the depths of the earth to the surface, hidden in the kimberlite, which is discovered and mining. Although human can produce artificial diamond, but the quality is far less than the size of natural diamond.

The nature of application

Not only can be processed into a very valuable diamond jewelry, also have a brilliant future in the industry. It has high hardness and good wear resistance, can be widely used for cutting, grinding, drilling; due to the thermal conductivity and good insulation, cooling plate as the semiconductor device; it has excellent light transmittance and corrosion resistance, in the electronics industry has also been widely used.

Development History

At the end of the 18th century, it was found that noble prestige diamond turned out to be an allotrope of carbon, since then, the preparation of artificial diamond becomes the glory and the dream of many scientists. A century later, graphite, carbon another elemental form was found, people will try to simulate the natural processes, graphite transformation to diamond at ultra high temperature and high pressure environment. In order to shorten the reaction time, the special conditions of high temperature and high pressure of 2000.

In 1955, American general electric company specializes in the manufacture of high temperature and high pressure electrostatic equipment, obtained in the world the first industrial use small synthetic diamond crystals, thus creating a precedent for the industrial scale production of synthetic diamond abrasives, now their annual output of about 20 tons; soon, Du Bang company invented the explosion, produced by the instantaneous explosion pressure and rapid warming, also won the the artificial diamond of a few millimeters in size.

The performance of diamond films is slightly less than that of diamond particles, and it is lower in density and hardness. Even so, its wear resistance is one of the highest and only 5 micron thick film, life expectancy is than that of hard alloy steel long 10 times above. We know that record stylus in contact surface of the tiny subjected to great pressure, while requiring a very long wear life, as long as on the head of a pin deposited a layer of diamond thin film, it can battle easily. If the use of diamond film on the outside of the plastic, glass to do wear resistant coating, can greatly expand its use, development of superior performance and economic products.

More important, the emergence of film to stone application can as the barriers of cutting tools, making them excellent heat, electricity, sound, light performance can give full play to. At present, diamond film has been used in semiconductor devices, optical acoustic devices, pressure processing and cutting tools, etc., its development speed is amazing, more attractive in the high-tech field.

Using artificial method to enable non diamond carbon conversion for the diamond structure of carbon and by nucleation and growth and the formation of single crystals and polycrystalline diamond, or the diamond particle in high pressure and high temperature sintered polycrystalline diamond (PCD). This is an important example of the application of high pressure research in production.

From the viewpoint of thermodynamics of determine whether non graphite diamond structure of carbonaceous materials into diamond phase transition condition is the free energy must be less than the former. This kind of transformation is in high pressure, high temperature or other components involved in conditions. Some of the pressure, temperature and components concentration can make the system can be changed, so that the price of electronic statistical weight changes at the level of the. This may occur in the electronic structure of electron transfer and form a new bonding state, namely the phase change. If the change in the energy system is conducive to change the electronic structure in a solid, high pressure and high temperature phase change occurs in the solid state, otherwise it may occur in the molten state or vapor. In the melt in the occurrence of this change is that the bonding character in the valence electron distribution statistical weight reduced accordingly, long-range order effect tends to disappear, changes in the atomic coordination number, while the electrons in excited state statistical weight tends to increase, short-range order effect was stronger. This change is that of elemental atoms or compounds bonding intermolecular electronic energy levels tend to disappear, all of the electron transfer to the single atom or molecule level up, so that the electron is in excited state statistical weight increase is more occurring in the gas. Therefore, the artificial diamond can be in the solid state, also can be in the molten state and vapor conditions, depending on the factors of pressure, temperature and component concentration caused by changes in the energy system. Starting from the view of dynamics, with appropriate transformation rate also requires transformation of graphite and other carbonaceous materials into diamond. The diamond nucleation rate and growth rate at the same time the maximum value when the phase change rate maximum.

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