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The colorless and transparent diamond has the best quality and can be processed into a dazzling gem after honing. Diamond is particularly hard, and it is at the highest level (10 levels) in Mohs hardness. It can be used to cut glass, engrave patterns on glass, or as a drill bit in geological drilling to drill the hardest rock. Diamond can also be made into turning tools, cutting hard alloys and steel; making grinding wheels and grinding hard materials. A diamond plate drilled with fine holes is called a die or a drawn diamond, and is used in the electrical industry to extract copper wire and tungsten wire having a diameter of only 0.001 to 0.2 cm.
Diamond is so expensive, chemists want to know what elements it is made of. In 1797, British chemist Qian Nan put the diamond in a sealed box made of gold, filling the box with oxygen. After the diamond is burned, it is determined that the composition of the gas in the box is carbon dioxide. In the above device, gold does not react with oxygen, then the composition of diamond can only be carbon. Qian Nan’s experimental results surprised people, and the chemical elements that make up this crystal clear gem are like the elements in the most common black coal .
There are not many diamonds in the world, and the deposits are concentrated in a few areas. Whether as a precious gem or industrial product, its demand far exceeds the amount of mining. Therefore, chemists and physicists began to explore the preparation of synthetic diamond. In this case, Muwasang began to study synthetic diamonds. Although the Swedish chemist Bajeli Ass commented on this research topic in 1830: "This is the same passion as an alchemist, but it may be a fantasy study." But Muwasang did not Therefore, loss of confidence.
At the beginning, Muwasang wanted to use the decomposition reaction of fluorinated hydrocarbons to make diamonds, and the result was amorphous carbon. Muwasang remembered Dobri's study of diamond-containing meteorites and the formation of the earth's crust in 1890. Dobri pointed out that diamond must be formed under high temperature and high pressure. In 1892, in the report of the French geologist Friedel to the French Academy of Sciences, he also mentioned that he found many fine diamonds in the meteorites found in Arizona.
Moisan also studied meteorites and meteorite iron Friedel mentioned, in addition to diamond-containing found, but also contain graphite and amorphous carbon. He also studied diamond-bearing rocks in Brazil and South Africa and found that it contained graphite and iron. These studies have led Muwasang to form the idea that graphite and amorphous carbon can be used as raw materials for synthetic diamond; diamond is formed in an iron-containing environment, so it can crystallize from carbon-containing iron.
Mowassan designed a method for preparing synthetic diamond by heating the metal iron in the graphite crucible in an electric furnace to melt the iron and be saturated with carbon. The molten iron in the graphite crucible is poured into cold water, and the carbon-containing iron expands as it turns into ice. Moreover, in such a rapid cooling process, the metal of the outer layer is always solidified first. When the internal metal begins to solidify, it creates a high pressure inside the metal. Under such conditions, a portion of the carbon crystallizes to form a black diamond. The solidified metal block was treated with a different acid, and the other materials were dissolved, leaving only the black diamond.
On February 6, 1893, the French Academy of Sciences held a meeting to discuss this discovery. The newspaper also published this news, so that precious stones can be prepared in a relatively simple way. This is incredible. The name of Muwasan has become a household name. . [next]
However, from 1894 to 1905, whether it was the repetitive experiment done by Muwasang himself or the verification experiment of Crooks et al. from 1894 to 1901, the diamond yields were very low, and the only one they could prove was This black substance is evidence of diamond, which produces carbon dioxide when burned in oxygen. In addition, synthetic diamond is much smaller than natural diamond, and the largest diamond made by Moissan is only 0.7 mm in diameter. Although Muwasan had been studying synthetic diamonds until his death, there was no cheap diamond with gemstone characteristics in the Mwasang era. Therefore, strictly speaking, Muwasang did not complete the development of synthetic diamonds. Since then, chemists, physicists, and engineers have studied the conditions of synthetic diamonds more systematically.
Many chemists used to heat diamond to 2000 ° C without air, and it turned into graphite.
C diamond—→C graphite If it is considered from the viewpoint of reaction reversibility, there seems to be a possibility that graphite is converted into diamond (C graphite—→C diamond), and the problem is how to promote this transformation.
From the crystal structure of diamond and graphite, each carbon atom in diamond is covalently bonded to four other carbon atoms, and the distance between carbon atoms is 154 pm; graphite is a layered structure in each layer, carbon The distance between the atoms is 142 pm, but the distance between the layers is relatively long, which is 337 pm. If sufficient pressure is applied to shorten the distance between the layers and the layers in the graphite structure, the carbon atoms between the layers and the layers are also covalently bonded, and the graphite becomes diamond.
To achieve this change, we must figure out what the conditions for the transition are. The density of graphite is 2.22 g/cm 3 and the density of diamond is 3.51 g/cm 3 . It can be seen that the reaction from graphite to diamond is a volume-reduced reaction. According to the Le Chatelier principle, increasing the pressure allows the reaction to proceed in a direction that decreases in volume. Therefore, from the perspective of chemical balance, to achieve the transition from graphite to diamond, the important reaction condition of synthetic diamond is high pressure.
In 1954, the engineers of the General Electric Company of the United States, Bendi and Hall, believed that the high temperature and high pressure could not be converted into diamonds only by short-term high temperature and high pressure. It is necessary to maintain high temperature and high pressure for a long time to promote this transformation. Perhaps this is They are different from the main features of Muwasang.
In addition, starting from the fact that the diamond in the vermiculite is embedded in iron sulfide, Benti et al. believe that the artificial diamond reaction should use iron sulfide as a flux.
So Bent, Hall and others designed a high temperature and high pressure device called Belt. In the graphite tube, the diamond seed crystal is placed in the iron sulfide flux, the graphite is contained therein, and the graphite cap is covered, and the metal crucible is used as the outer casing of the device. At 9625 MPa and 1650 ° C, the graphite is finally converted into diamond after a long period of reaction.
In 1955, General Electric Company of the United States announced the news of successful trials of synthetic diamonds, and proved that they obtained diamonds by the following facts: (1) The structure of natural diamond and synthetic diamond was determined by X-ray diffraction experiments, and the diffraction patterns of the two were exactly the same. . (2) The hardness of synthetic diamond and natural diamond is exactly the same. (3) Ask other scientists to repeat the test with more than 100 tests using the Bertel device designed by the company. The results of each time are the same as those of Bundi, Hall, etc. These three are really ironclad and indisputably explain this. It is indeed diamond synthesized by Di, Hall and others. This extremely difficult man-made material was finally created by scientists.
Birth of synthetic diamond
In 1892, Muwasang began researching synthetic diamonds . In the natural substances, maximum hardness of diamond, its beautiful and transparent, and dazzling, from time immemorial attracted people's attention. Bronze statue on display by the Greeks produced a 5th century BC in the British Museum in London, the statue's eyes are made with two diamonds. This shows how long people have used diamonds. The famous natural scientist of the Roman era, Pliny, highly praised diamonds in the book "History of Nature": "Not only in all kinds of gems , but also in the material wealth of human beings." Diamond is also considered to be the most valuable thing in the world. For a long time, only a few kings have the king of such precious gems."