Diamond is what we call diamond, a mineral made of pure carbon. Diamond is the hardest substance in nature, so it has many important industrial applications, such as fine grinding materials, high-hardness cutting tools, various kinds of drills, wire drawing dies. It is also used as part of many precision instruments.
Diamonds come in all kinds of colors, from colorless to black, especially colorless. They can be transparent, translucent or opaque. Most diamonds have a yellow tint. Diamond has a very high refractive index and a very high dispersion, which is why diamonds reflect colorful flashes. Diamonds glow blue-green when exposed to x-rays. Diamonds are produced only in kimberlite tubs. Kimberlite is their native rock, and diamonds from other places are carried by rivers, glaciers, etc. Diamonds are generally granular. If the diamond is heated to 1000℃, it will slowly turn into graphite.
Diamond and graphite belong to the elemental form of carbon. It is a kind of super-hard, wear resistance, thermal sensitivity, heat conduction, semiconductor and penetration and other excellent physical properties, known as the “king of hardness” and the king of gems lauded, the crystal Angle of a diamond is 54 degrees 44 minutes 8 seconds. In the 1950s, the United States successfully manufactured synthetic diamonds from graphite under high temperature and high pressure. At present, synthetic diamond has been widely used in production and life, but it is still difficult to make large particles of a diamond.
The chemical composition of natural diamond is C, which is the same as graphite, which is the same as carbon. In the chemical composition of minerals, it always contains Si, Mg, Al, Ca, Mn, Ni and other elements, and often contains Na, B, Cu, Fe, Co, Cr, Ti, N, and other impurities, as well as carbohydrates.
The diamond mineral crystal structure belongs to the coaxial crystal system homopolar tetrahedral structure. Carbon atoms are located at the top and center of the tetrahedron and have a high degree of symmetry. The common crystal shapes are octahedron, diamond dodecahedron, cube, tetrahedron, and hexahedron.
Mineral brittle, shell-shaped or staggered fractures, cleavage along the cleavage plane of the crystal at low impact, medium or complete cleavage with the parallel octahedron, incomplete cleavage with the parallel dodecahedron. The mineral is pure with a density of 3 470-3 560kg/m3.
The color of a diamond depends on the degree of purity, the type and content of impurities contained in it. Extremely pure diamond is colorless, usually yellow, brown, gray, green, blue, milky white and purple in different degrees. Pure transparent, translucent or opaque with impurities. Under cathode ray, X-ray and ultraviolet ray, different green, sky blue, purple, yellow-green and other colors of fluorescence will be emitted. Light bluish phosphorescence in dark room after sunlight exposure. Diamond luster, few grease or metallic luster, high refractive index, generally 2.40-2.48.
Thermal conductivity of diamond general 136.16 w/(m k), including Ⅱ type a diamond high thermal conductivity, at liquid nitrogen temperature is 25 times that of the copper, and along with the rise of temperature fell sharply, such as 5 times at room temperature for copper. The specific heat capacity increases with temperature rise, such as 399.84j/(kg·k) at -106℃ and 472.27j/(kg·k) at 107℃. The coefficient of thermal expansion is very small and increases with the rise in temperature. For example, it is 0 at -38.8℃ and 5.6×10-7 at 0℃. The ignition point is 720 ~ 800℃ in pure oxygen, 850-1 000℃ in air, and 2 000-3 000℃ in oxygen.
The chemical properties of diamond are stable, with acid and alkali resistance. It does not react with concentrated HF, HCl, and HNO3 at high temperatures. It only oxidizes slightly on the surface when boiled with the mixture of K2Cr2O7 and H2SO4 in the molten body of Na2CO3, NaNO3, and KNO3.Corrosion in high-temperature gas of O, CO, CO2, H, Cl, H2O, and CH4.
Diamond also has non – magnetic, poor conductivity, hydrophilic hydrophobicity, and friction electricity. Only Ⅱ b type diamond with good performance of semiconductor. According to the diamond nitrogen impurity content and differences in thermal, electrical and optical properties, the diamond can be divided into Ⅰ type and Ⅱ type two kinds, and further subdivided into Ⅰ, Ⅰ b, a and b Ⅱ Ⅱ four subgroups. Ⅰ type diamond, especially Ⅰ type a, for a common ordinary diamond, accounts for about 98% of the total natural diamond. Ⅰ type diamond all contains a certain amount of nitrogen, has good thermal conductivity, poor conductivity, and good crystal shape. Ⅱ type diamond is rare, with little or almost no nitrogen, good thermal conductivity and surface characteristics of the crystal. Ⅱ subtype b diamond half electrical conductivity. Due to the excellent Ⅱ type diamond, so much used in space technology and cutting-edge industries.
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