Diamond, commonly known as "Jin Gangzuan", is a mineral composed of allotrope carbon of graphite with chemical formula C, and it is also the precursor of ordinary diamond. Diamonds are the hardest substance in nature. Graphite can form synthetic diamond at high temperature and high pressure. Diamonds are widely used, such as handicrafts, industrial cutting tools, and also a precious gem.
20 18, 18 In February, a yellow diamond weighing 552 carats was unearthed in Canada, making it the largest diamond found in North America.
stability
Diamond is chemically stable, acid-resistant and alkali-resistant, and does not react with concentrated HF, HCl and HNO3 at high temperature. The surface of diamond will be slightly oxidized only when it is boiled in the melt of Na2CO3, NaNO3 and KNO3 or in the mixture of K2Cr2O7 and H2SO4. Corrosion in high temperature gases of O, Co, CO2, H, Cl, H2O and CH4.
Diamond also has non-magnetism, poor conductivity, oleophilic hydrophobicity and triboelectricity. Only Ⅱ B diamond has good semiconductor properties. According to the difference of nitrogen impurity content and thermal, electrical and optical properties of diamonds, diamonds can be divided into two categories: type I and type II, and further subdivided into four subcategories: 1a, 1b, 2a and 2b. Type Ⅰ diamond, especially subtype Ⅰ A, is a common common diamond, accounting for about 98% of the total natural diamonds. Type I diamonds contain a certain amount of nitrogen, which has good thermal conductivity, poor electrical conductivity and good crystal shape. Type ⅱ diamond is extremely rare, with little or no nitrogen content, and has the characteristics of good thermal conductivity and crystal bending. Diamonds of type Ⅱ b are semiconductors. Second-class diamonds are mostly used in aerospace technology and cutting-edge industries because of their excellent properties.
The world's largest industrial diamonds and gem-grade diamonds both exceed 365,438+000 carats (65,438+0 carats = 200mg). Among them, the gem-grade diamond with the size of 10× 6.5× 5cm was named "Cullinan" and was discovered in Premil Rock Tube in 1905. China Changlin diamond, weighing 158.786 carats, was discovered by Wei Yu 1977, a female member of Changlin Brigade in Linshu County, Shandong Province, and was later listed as a world-famous diamond. The main diamond producing areas in the world are South Africa, Australia, Zaire, Botswana and Russia.
synthetic diamond
There are two main methods to synthesize diamond, high temperature and high pressure method and chemical vapor deposition method.
The technology of high temperature and high pressure method is very mature and has formed an industry. The domestic output is extremely high, ranking first in the world.
Chemical vapor deposition still mainly exists in the laboratory. The team of Professor Shan Chongxin from Zhengzhou University developed the process of synthesizing diamond single crystal and carat diamond by chemical vapor deposition, and synthesized high-quality diamond with a mass greater than 1.2 carat, white color and Si 1.