Is it possible to get diamond from coal?

Уcarbon was known to ancient peoples in prehistoric times in the form of charcoal, soot and coal. According to the Roman historian Vitruvius, soot in his time was produced in large quantities and was used to make paint used in fresco painting and ink. The method of producing soot, according to Vitruvius, was as follows: resin, tar, resinous chips, vines and similar materials were burned on a hearth, and flame and smoke were passed through holes into a chamber with marble walls; the settled soot was removed and then ground with glue, gum and vitriol. Since time immemorial, the Chinese have used soot to prepare carcass, which then spread to Korea, Japan and the peoples of the Middle East (IV century BC). In Europe, ink became known only in the 15th–16th centuries. The production of coal has also been known since ancient times. It can be considered a firmly established fact that coal was part of the incendiary substances used in ancient times. Diamond appeared as jewelry at the beginning of our era and, in all likelihood, was brought from India or from the island of Borneo, where there are its deposits. Large, beautifully cut diamonds were considered the best decoration for the treasuries of rulers and were often obtained through violence and blood. These are the famous diamonds “Regent”, “Koh-i-Noor”, “Great Mogul”, “Southern Star”, “Hope”, “Shah”. With the last diamond, the Shah of Persia paid Tsar Nicholas I for the blood of the Russian ambassador A.S. Griboedov, the author of the comedy “Woe from Wit,” who was treacherously killed in Tehran. The entire history of the Shah diamond is associated with violence and crime. The largest known diamond, the Cullinan, was found in 1905 in South Africa. Its weight is 621 g, and its size is 10x6x5 cm. The Diamond Fund of our country stores one of the largest and most beautiful diamonds in the world – “Orlov” (37,92 g). Diamonds have long attracted attention due to other qualities. Even in ancient India, diamonds were used to process precious stones. The Greeks and Romans used it for the same purpose. Alchemists could not ignore this mineral, the highest in its hardness, insoluble in acids, incombustible in ordinary fire: they also looked for clues to the “philosopher’s stone” in diamond. В 1781 A.L. Lavoisier proved that when coal is burned, “carbonic acid” (carbon dioxide) is produced, which is nothing more than a combination of the “chemical principle of coal” (i.e. the element carbon) with oxygen. The true nature of the diamond was discovered only in the 70s. XVIII century, i.e. on the threshold of the great chemical revolution. Until this time, no one could have imagined that a brilliant mineral, playing with all the colors of the rainbow, had something in common with amorphous and black coal. Briefly summarized, the history of establishing the true chemical nature of diamond is as follows. In the 17th century Axel de Bout, and then I. Newton, suggested, based on the similarity of the refractive indices of turpentine, camphor and diamond, that the latter should burn. In 1694, Florentine academics conducted an experiment of burning a diamond at the focus of a concave mirror. They were convinced that a diamond under these conditions first smolders like coal and then burns out completely. F. Lorenz then established that diamond burns without a residue in the flame of a forge. All these experiments, however, caused extreme mistrust, because The general opinion of jewelers and mineralogists was that diamond is a type of quartz. Many prominent chemists of that time did not agree with the conclusion that diamond could burn. For example, G. Ruel (Lavoisier’s teacher) and some other chemists who conducted experiments with diamonds came to the conclusion that they evaporate when exposed to high temperatures. In 1772, Lavoisier, together with other scientists, conducted a series of experiments to study the relationship of various bodies to heating at the focus of solar rays, collected using a huge lens (about 1,5 m in diameter). Based on the results of his research, he published two works “On the destruction of diamond by fire”, in which he finally proved that when burning a diamond, as when burning charcoal, nothing else is produced except for “binding air” (carbon dioxide), and that when burning a diamond some of the air is also absorbed, as was observed during the combustion of phosphorus or coal. In 1797, the English chemist S. Tennant, after a series of experiments, came to the conclusion that diamond is the purest carbon. He burned equal amounts of diamond and coal and was convinced that exactly the same volumes of carbon monoxide were formed. This proved that diamond is a kind of modification of carbon. Somewhat earlier, in 1779, the Swedish chemist K. Scheele suggested that graphite was also a mineral coal. He managed later, in 1789, to prove that graphite burns well in a stream of hydrogen, and in 1792 he came to the final conclusion that graphite and coal are modifications of the same element. In 1799, Guiton de Morveau observed the transition of diamond into graphite when the former was heated in vessels without access to air. At the same time, he discovered that graphite and some other bodies, such as coke, produce only carbon dioxide when burned. Repeating Tennant’s experiment, but adding graphite to the list of combustible substances, de Morveau established an important fact: if equal amounts of graphite, diamond and coal are burned by weight, then equal amounts of carbon dioxide are obtained. J.Ya. Berzelius in 1841 first described coal (soot), diamond and graphite as modifications of the same element and introduced a new concept of “allotropy” into chemistry. Latin name “carboneum” carbon received from the word “carbo” – coal, which in turn originates from Sanskrit cra – burn. The name “graphite” (from the Greek. graph – I am writing) was given by the mineralogist A.G. Werner in 1789 after Scheele’s experiments. In Russian literature, graphite at the beginning of the XNUMXth century. was called “pencil” (from the Mongolian “kara” – black, “tash” – stone), and carbon – “carbon solution”. The word “diamond” and Western European “diamant” – of Arabic origin and means the hardest. The Greeks and Romans called this mineral adamas. In a more or less modified form, this word passed into all European languages. Translated, it means unchanging, indomitable, inaccessible, since the diamond did not yield to the hand of the grinder. Only in the 13th century. The Dutchman Van Berkem guessed to grind these stones against each other and thus rediscovered the method of polishing diamonds, which had long been known in India. ОThe problem of obtaining an artificial diamond is very interesting. Interest in it is aroused not only by the industrial and economic significance of this material, but also by the tempting nature of solving a purely scientific problem. Attempts to produce diamonds artificially began immediately after it was discovered that diamonds were the purest carbon. They were very numerous. We will not dwell on their description in detail and will name only a few of them. In 1880, the English chemist J. Hennay obtained several crystals by prolonged heating of light hydrocarbons with lithium metal in an iron welded tube. These crystals, by their properties, could be classified as a type of diamond, which, however, is not found in nature. These diamonds are still kept in the British Museum. An X-ray examination of them in 1943 confirmed that these were real diamonds. The most popular were the experiments of the French scientist A. Moissan, conducted by him in 1893–1896. Moissan melted iron at temperatures of 2000–3500 °C and high pressure, to which he added pure coal powder. The molten iron was then poured into a hollow copper vessel, cooled externally with water. The frozen mass was treated with acids to remove iron, silicates, carbide and graphite. After this complex processing of the alloy, black transparent crystals remained, scratching the ruby ​​and burning in oxygen. The largest of them were no more than 5 mm in diameter. Moissan mistook them for diamonds. His experiments were repeated by many scientists and always led to inconclusive or contradictory results. Regarding all attempts to obtain an artificial diamond, the German chemist Otto Ruff concluded: “Except for Moissan, no one succeeded in obtaining an artificial diamond. It is possible that Moissan received it, but this has not been proven. ” However, the path to resolving the problem was not closed. The fact is that most of the experiments were carried out at a time when the question of the comparative stability in terrestrial conditions of both modifications of carbon – diamond and graphite – had not yet been resolved. An employee of the Institute of Chemical Physics of the USSR Academy of Sciences O.I. Leypunsky in the article “On artificial diamonds” (1939) explained that the main reason for the failures of researchers was that “. all attempts to make diamond were made under conditions under which graphite is a more stable solid phase than diamond.” The scientist calculated that to successfully obtain a diamond, “first, the graphite must be heated to at least 2000 K” so that the carbon atoms can move from place to place. Secondly, it must be compressed with monstrous pressure, no less than 60 thousand atmospheres. Then it will definitely turn into a diamond, just as a stone thrown by a hand will definitely rise into the air.” These theoretical calculations were brilliantly confirmed in 1955, when American scientists F.P. Bandy, G.T. Hall, G.M. Strong and R.G. Ventorf, after eight years of experiments, managed to synthesize real diamonds under conditions close to those mentioned higher. And yet, in one experiment, the researchers obtained no more than 20 mg of diamonds, and the largest of them was only 1,2 mm long. В Unlike diamond, artificial graphite is produced and used industrially on a large scale. It is obtained by heating coal to a temperature of 2200–2500 °C in an electric furnace. The cost of producing artificial graphite does not exceed the cost of obtaining natural graphite of high purity. What is the reason for the formation from atoms of the same element of substances so different in their physical properties – the hardest, shiny diamond and soft, easily abraded black graphite? Science now gives an exact answer to this question. It is now firmly established that the sharp difference in the properties of diamond and graphite is explained by the difference in their internal structure. In diamond crystals, all carbon atoms are located at equal distances from each other (1,54): each atom in diamond is located in the center of a regular tetrahedron, at the vertices of which other atoms are located. This structure gives the diamond extraordinary hardness. It is the hardest of all substances known in nature.

Arrangement of carbon atoms in diamond

The structure of graphite is completely different: it is formed by parallel layers consisting of carbon atoms located at the corners of regular hexagons at a distance of 1,42; the layers are separated from each other at a much greater distance – 3,39 and are also shifted relative to each other. This structure determines the property of graphite to exfoliate into flakes, due to which it is used for the manufacture of pencils and as a lubricant.

Arrangement of carbon atoms in graphite

Coal (soot or soot, wood, bone, coke and other varieties) differs from diamond and graphite in that it does not have any crystalline structure. Coal powder, like lump coal, has many valuable properties, the most important of which is its ability to adsorb various gaseous and solid substances. This property was discovered in 1785 by the Russian chemist, academician T.E. Lovitz and immediately found wide application in laboratory, pharmaceutical and industrial practice. Diamond is the hardest mineral on the Mohs hardness scale. There is nothing harder than him. However, diamond is just carbon. Like coal or graphite. Only, unlike them, the carbon atoms in diamond took on a cubic allotropic form. People’s love for diamonds is very strong Photo: pixabay.com

Squeeze a piece of coal hard enough and you get a diamond.

Ever since people learned that diamond is carbon, like coal, attempts have been made regularly to compress a piece of coal hard enough to make a diamond. What is the difference between diamond substitutes and artificial rubies and sapphires. emeralds? People create artificial rubies, sapphires, spinels, and emeralds using the same methods that nature once created real rubies and emeralds. And diamond substitutes, artificial diamonds, are crystals of a different composition than diamond crystals. They are simply similar to real diamonds in terms of refraction and the play of light, but they have a completely different chemical composition. From the moment people learned to polish diamonds into sparkling diamonds, diamond counterfeiting has been developing. At first, fakes were made from plain glass, then from lead glass. Soon, distinguishing rhinestones from diamonds became a difficult task. Quite often it was possible to come up with very successful substitutes for jewelry diamonds.

Hollywood stars and some queens, owners of unique diamonds, often preferred to wear skillfully made rhinestones at social events – substitutes for their unique diamonds.

Just to save money: such a rhinestone, almost indistinguishable from the original, cost a little more than Lloyd’s insurance against theft for one evening. But there has never been a man-made diamond that is completely identical to the original. The fakes were revealed by a play of light (dispersion) that was different from that of a diamond; all of them, without exception, were much less durable, many of them were visible in X-rays differently than a diamond. It was always possible to distinguish a fake. True, sometimes only with the help of sophisticated equipment. But in 1956, General Electric announced the successful synthesis of diamonds. Several years passed and the production of synthetic industrial diamonds began to flow. Thousands and millions of carats were produced using sophisticated equipment. Synthetic diamonds have become an important part of technology development. Cutting tools reinforced with small diamond crystals have proven to be much more durable than similar tools made from the best alloys. Demand for industrial diamonds was growing. Before World War II, up to 7 million carats of industrial diamonds were consumed annually in technology. Once the production of synthetic diamonds was established, the consumption of industrial diamonds began to grow rapidly.

In 1970, 70 million carats were already used in technology, by 1990 – about 250 million carats. By 2010, industrial diamond production increased to 5 billion carats. Currently, the world produces about 10 billion carats synthetic technical diamonds.

Moreover, since the beginning of the 80st century, China has been leading in the production of synthetic diamonds, producing about 2014% of the global diamond production. At the same time, 131.1 million carats of jewelry diamonds were mined in XNUMX. For the most part, very small diamond crystals and diamond dust are now synthesized. They are used in the production of all kinds of grinding pastes, and in addition, synthetic diamonds are part of numerous stone-cutting and metalworking tools. Diamond glass cutters, drills, drill bits, saws, cutters and dies work many times longer and better than their predecessors made of special steel alloys. Moreover, the price of synthetic diamonds has already dropped to about $1 per carat. Now, according to experts, there are only about 1000 diamond synthesis plants operating worldwide. The very first installations used synthesis technology using high pressure and temperature (HPHT), but at the end of the XNUMXth century, the technology for producing diamonds using carbon vapor deposition (CVD) was discovered. Both of these methods are related to each other.

The HPHT method produces a small crystal, which subsequently serves as a seed for the CVD method.

Using a combination of both methods, scientists have developed techniques for producing diamond wafers, which have already found application in electronics. By increasing the size of these plates, their widespread use will become possible, including as glass for watches. Diamond wafers are believed to be a possible future basis for electronics. In addition to the production of industrial diamonds, which have long since reliably occupied their niche in world technologies, attempts to synthesize gem-quality diamonds continue. Actually, the fundamental possibility of this was proven back in the 70s, when several jewelry diamonds were produced in the USSR for testing (the jeweler who polished them mistook them for small diamonds from Sierra Leone). However, obviously, their price was so high that the experiment was not continued; jewelry diamonds are practically still mined only “from the earth” – which was produced by nature many hundreds of millions of years ago. But scientists do not despair. New technologies for diamond synthesis have already appeared. In order to obtain a 1-carat diamond using HPHT technology, the installation must operate continuously for approximately 5 days (which greatly increases the price of the resulting diamond). Currently, in China, combining HPHT and CVD technologies, “diamond blanks” of cylindrical and cubic shapes are obtained. These are diamonds, but compared to real diamond crystals they have an irregular structure. But technology does not stand still. We can confidently say that over time, diamonds synthesized by man will not differ at all from real ones, because people’s love for diamonds is very strong.