Graphite and diamond: crystal lattice and properties. Allotropic substances: diamond and graphite. Formula of graphite and diamond

Not everyone knows, but diamond and graphite are two forms of the same substance. These minerals are completely different from each other in hardness and in the characteristics of refraction and reflection of light. And the differences are quite significant. Diamond is the hardest mineral in the world, on the Mohs scale it is a standard - 10, while the hardness of graphite on this scale is only 2. Thus, diamond and graphite are both the most similar and dissimilar substances in the world.

Crystal lattices of diamond and graphite

Each of them comes from carbon, which, in turn, is the most abundant element in the biosphere. It is present both in the atmosphere and in water, in biological objects. In the ground, it is present in the composition of oil, gas, peat, and so on. It is also found as deposits of graphite and diamond.

Most carbon in organisms. Moreover, none of them can do without it. And the origin of this mineral in other parts of the planet is precisely explained by the presence of living organisms there once.

A lot of controversy accompanies the question of where graphite and diamonds came from, because it is not enough that there is one carbon, it is also necessary that certain conditions, at which this chemical element takes on a new structure. It is believed that the origin of graphite is metamorphic, and that of diamonds is igneous. This means that the formation of diamonds on the planet is accompanied by complex physical processes, most likely in the deep layers of the earth during combustion and explosions in the presence of oxygen. Scientists suggest that methane is also involved in this process, but no one knows for sure.

Differences between graphite and diamond

The main difference is the structure of diamond and graphite. Diamond is a mineral, a form of carbon. It is characterized by metastability, which means that it is able to remain unchanged indefinitely. Diamond transforms into graphite under some specific conditions, such as high temperature in a vacuum.

Graphite is also a modification of carbon. Its structure makes the mineral very layered, so its most common use is in the manufacture of pencil leads.

The phenomenon in which substances formed by the same chemical element have different physical properties is called allotropy. There are other similar substances, but these two minerals have the greatest difference between them. The decisive role in this is played by the structural features of the crystal structure of each of the minerals.

Diamond has an incredibly strong bond between atoms, due to their dense arrangement. Adjacent atoms of the cell have the shape of a cube, where the particles are located on the corners, faces and inside them. This is a tetrahedral type of structure. This geometry of atoms provides the most dense organization. That is why the hardness of diamond is so high.

The low atomic number of carbon, showing that the atom has a small atomic mass and, accordingly, a radius, makes it the hardest substance on the planet. However, this does not mean durability at all. Breaking a diamond is quite easy, just hit it. This structure explains the high coefficient of thermal conductivity and light refraction of diamond.

The structure of graphite is completely different. At the atomic level, it is a series of layers located in different planes. Each of these layers are hexagons that adjoin each other like a honeycomb. In this case, only atoms located within each layer have a strong bond, and the bond between the layers is fragile, they are practically independent of each other.

The trace from the pencil is just the detachable layers of graphite. Due to the peculiarities of its structure, graphite has a nondescript appearance, absorbs light, has electrical conductivity and a metallic luster.

Getting diamond from graphite

For a long time, it was technologically difficult to obtain a diamond, but today this is not such a difficult task. The main problem is the repetition of processes in the laboratory in a short period of time, which in nature take millions of years. Scientists have proven that the conditions for the transition of diamond from graphite was heat and pressure.

For the first time such conditions were obtained with the help of an explosion. Explosion is chemical process, which is combustion at high temperature and speed. After that, they collected the remains of graphite, and it turned out that small diamonds formed inside it. That is, the transformation took place only fragmentarily. The reason for this is the spread of parameters within the explosion itself. Where conditions were sufficient for such a transformation, it happened.

Natural rough diamond

Such parameters made explosions unpromising for diamond production. However, the experiments did not stop; for a long time, scientists continued to conduct them in order to somehow obtain this mineral. A more or less stable result was obtained when they tried to heat the graphite impulsively to a temperature of two thousand degrees. In this case, it was possible to obtain diamonds of decent size.

However, such experiments gave another unexpected result. After the transformation of graphite into diamond, a reverse transition of diamond into graphite occurred with a decrease in pressure, that is, graphitization occurred. Thus, obtaining a stable result with only one pressure could not be achieved. Then, together with an increase in pressure, graphite began to be heated. Some time later, it was possible to calculate the range of pressures and temperatures at which diamond crystals could be obtained. However, these methods still did not allow obtaining a gem-quality mineral.

In order to obtain stones suitable for creating jewelry, they began to grow diamonds using a seed. As it was used a ready-made diamond crystal, which was heated to a temperature of 1500 degrees, which stimulated first rapid and then slow growth. However, the application of the method on an industrial scale was unprofitable. Then they began to use methane as a top dressing, which under such conditions decomposed into carbon and hydrogen. It was this carbon that acted, if I may say so, as the diamond's fodder, allowing it to grow much faster.

So today this method is used to create artificial diamonds. Although cost-effective, the cost of such whole man-made minerals remains high, making them less popular than diamond substitutes.

Mineral deposits

Diamonds are born at a depth of 100 km and at a temperature of 1300 degrees. Kimberlite magma, which forms kimberlite pipes, comes into action as a result of explosions. It is these pipes that are the primary deposits of diamonds. For the first time, such a pipe was discovered in the African province of Kimberley, hence its name.

The most famous deposits are in India, Russia and South Africa. Primary deposits account for 80% of all mined diamonds.

To find a diamond in nature, X-rays are used. Most of the stones that are found are unsuitable for jewelry production, as they have a significant number of defects, including cracks, inclusions, extraneous shades of fluorescence, and so on. Therefore, their application is technical. Such stones are divided into three categories:

board - stones with zonal structure;
ballas - stones that have a round or pear-shaped shape;
carbonado - black diamond.

Diamonds big size with outstanding performance tend to get their name. Besides, high price stone makes it desirable for many, which guarantees a "bloody story".

Graphite is formed as a result of alteration of sedimentary rocks. In Mexico and Madagascar, low quality graphite ore can be found. The most famous deposits are in Krasnodar and Ukraine.

Application

The use of both diamond and graphite is much wider than it seems. There are several uses for diamonds.

IN jewelry industry diamonds are used only in cutting, as you know, they are called brilliants. Only 20% of all mined stones are suitable for jewelry, and there are much fewer high-quality minerals.

Diamonds are the most expensive stones in the world. In terms of value, only some copies of rubies can be compared with them. The value of minerals is affected by cut, color, hue and clarity. Usually, some of these characteristics are invisible to the naked eye, but are revealed during the examination.

The use of diamonds in jewelry is very common. Often they act as the only stone or complement high-quality sapphires, rubies, emeralds. Most frequent use stones - engagement rings.

In the technical field, they usually take second-rate raw materials, with defects or various shades. Technical diamonds are divided into several subcategories.

diamonds of a certain shape, which is suitable for the manufacture of bearings, drill tips and so on;
raw stones;
pebbles with defects, used only for making diamond chips and powder.

The latter are used either in very small parts or as a coating for the manufacture of cutting and grinding tools.

In electronics, needles are used, which are raw crystals that naturally have a sharp top, or fragments with the same top. Drilling rigs in the industry also contain diamonds. Layers of this mineral are used in microcircuits, counters, and so on, this is due to the high thermal conductivity and resistance.

About 60% of all industrial diamonds are used in tools. The remaining 40% in equal amounts:

when drilling wells;
processing;
in small details of jewelry;
in grinding wheels.

IN pure form graphite is not used. It is usually processed. Graphite highest quality used in the form of a pencil rod. Graphite finds the widest application in casting. Here it is used to ensure a smooth surface of the steel. For this, it is used in its raw form.

In the electric coal industry, not only a mineral of natural origin is used, but also a created one. The latter has high uniformity in quality and purity. The high current conductivity makes it also widely used for the manufacture of electrodes in instruments. In addition, it is used as motor brushes. In metallurgy, graphite is used as a lubricant.

Graphite rods, for their ability to slow down neutrons, were previously widely used in the creation of nuclear reactors. In particular, it was boron rods with graphite tips that acted as control-protection rods at the Chernobyl nuclear power plant. One of the problems that later led to the accident was that in order to extinguish the chain reaction, it was necessary to absorb neutrons, for which boron was responsible, and not to slow down. Therefore, at the moment when the rods were lowered into the reactor core, its energy increased abruptly, which led to overheating. But that was just one of many reasons.

So diamond and graphite are two different minerals with the same element at the base. Their structures make the properties different, which is of interest. Each of them is beautiful in its own way and has a very wide application both in very complex structures and in everyday objects.

For ordinary person diamond and graphite are two completely different and unrelated elements. Diamond evokes associations with iridescent jewels, the expression “glitters like a diamond” is recalled. Graphite is something gray that is usually used to make pencil leads.

It is hard to believe that both minerals are the same substance with different forms of processing.

The concept and main characteristics of minerals

A diamond is a transparent crystal that has no color and has high light refraction characteristics. The following main properties of the mineral are distinguished:

Nature generates both diamonds of certain shapes and in several crystalline forms, which is due to its internal structure. Pronounced crystals have the shape of a cube or tetrahedron with flat faces. Sometimes the edges seem to be embossed due to the presence of numerous outgrowths and transformations invisible to the eye.

Although many consider diamond to be the most durable material in the world, but science knows a substance that is superior to diamond in strength by more than 11% - “hyperdiamond”.

Graphite is a gray-black crystalline substance with a metallic luster. The composition of graphite has a layered structure, its crystals consist of small thin plates. It is a very fragile mineral, resembling appearance steel or cast iron. Graphite has a low heat capacity but a high melting point. In addition, this mineral:

Graphite is greasy to the touch, and leaves traces when swiped on paper. This is due to the fact that the atoms of the crystal lattice are weakly bonded.

The difference between graphite and diamond, structural features and the process of transition of one mineral to another

Diamond and graphite are allotropic minerals with respect to each other, that is, they have various properties, but are different forms carbon. Their main difference lies only in the chemical structure of the crystal lattice.

The crystal lattice of diamond has the form of a tetrahedron, in which each atom is surrounded by 4 more atoms and is the top of the neighboring tetrahedron, forming an infinite number of atoms with strong covalent bonds.

Graphite at the atomic level consists of layers of hexagons with vertices-atoms. The atoms are well connected to each other only at the level of layers, but the layers do not have a strong connection between themselves, which makes graphite soft and unstable to destruction. It is this feature that makes it possible to obtain a diamond from graphite.

Physical and Chemical properties diamond and graphite are clearly visible from the table.

Characteristic
The structure of the atomic lattice	cubic shape	Hexagonal
Light transmission	Conducts light well	Doesn't let light through
electrical conductivity	Doesn't have	Has good electrical conductivity
Atom bonds	Spatial	planar
Structure	Hardness and brittleness	Layering
The maximum temperature at which the mineral remains unchanged	720 Celsius	3700 Celsius
Color	White, blue, black, yellow, colorless	Black, grey, steel
Density	3560 kg/m3	2230 kg/m3
Usage	Jewelery, industry	Foundry, electric coal industry.
Mohs hardness	10	1

The chemical formula of diamond and graphite is the same - carbon (C), but the process of creation in nature is different. Diamond occurs at very high pressures and instantaneous cooling, while graphite, on the contrary, at low pressure and high temperature.

There are the following methods for obtaining diamonds:

The process of diamond to graphite is similar. The only difference is in pressure and temperature.

Mineral deposit

Diamonds lie at depths of more than 100 km at a temperature of 1300 ̊С. From the blast wave, kimberlite magma comes into action, forming the so-called kimberlite pipes, which are the primary deposits of diamonds.

The kimberlite pipe is named after the African province of Kimberley, where it was first discovered. Rocks with diamond deposits are called kimberlites.

The most famous deposits are now in India, South Africa and Russia. Up to 80% of all diamonds are mined at primary deposits, consisting of kimberlite and lamproite pipes.

X-rays help find diamonds in the mined rock. Most of the found stones are used in industry, as they do not have sufficient characteristics for the jewelry field. Industrial stones are divided into 3 types:

board - small stones with a granular structure;
ballas - round or pear-shaped stones;
carbonado is a black stone that got its name from its resemblance to coal.

It is curious that the largest and most outstanding diamonds receive their unique name. The most famous of them are Shah, Star of Minas, Kohinoor, Star of the South, President Vargas, Minas Gerais, English Diamond of Dresden, etc.

Graphite is formed as a result of the modification of sedimentary rocks. Mexican, Noginsk and Madagascar graphite deposits are rich in ore with low quality graphite. Less common, the Botogol and Ceylon types, are distinguished by ore rich in high graphite content. The largest known deposits are located in Ukraine and in the Krasnodar Territory.

Scope of application

Diamond and graphite are used much more widely than it might seem at first glance. Diamonds have found their application in the following areas:

As a percentage of the use of diamonds, it looks like this:

Tools, machine parts - 60%.
Framing of grinding wheels -10%.
Wire recycling-10%.
Well drilling - 10%.
Jewelry, small parts – 10%.

As for graphite, it is practically not used in its pure form, but is subjected to pre-treatment, although graphite of different quality is used in different areas. The highest quality graphite is used for stationery pencils. It has found its widest application in the foundry industry, providing a smooth surface to various forms of steel. Almost untreated graphite is used here.

The electric coal industry, along with natural graphite, uses artificially created graphite, which is also widely used due to its special purity and consistency of composition. Electrical conductivity made graphite a material for electrodes electrical appliances. In metallurgy, it is used as a lubricant.

Diamond and graphite are identical in composition, but unique in their own way. The benefits of graphite for various industries industry is much higher than diamond.

The diamond, designed to delight with its beauty, is invaluable for the economy, bringing huge profits from its use in the jewelry industry.

A hard diamond that plays in the light and an opaque, easily peeling graphite can be figuratively called siblings. After all, in the chemical composition of both there is a single element - carbon. Let us find out why, having a common origin, these minerals are so different from each other and how diamond differs from graphite.

Definition

Diamond- a mineral, the basis of which is carbon. It is characterized by metastability, that is, the ability to normal conditions exist indefinitely unchanged. Placing a diamond in specific conditions, such as a vacuum at elevated temperature, leads to its transition to graphite.

Diamond

Graphite- a mineral that acts as a modification of carbon. During friction, flakes are separated from the total mass of the substance. Most known use graphite - the manufacture of a pencil lead from it.

Graphite

Comparison

The phenomenon in which substances have different properties, but are formed by a common chemical element, is called allotropy. However, in nature, perhaps, there are no more such completely different allotropic forms of the same element. What explains the difference between diamond and graphite?

The decisive role here is played by the features of the crystal structure of each of the substances. Let's talk about a diamond. The bond between its atoms is incredibly strong. This is due to the way they are located relative to each other. Adjacent atomic cells of a substance have a cubic shape. The particles are located in the corners of the cells, on their faces and inside them. This type of structure is called tetrahedral.

diamond cell

This geometry of atoms provides the most dense organization of them, due to which the diamond becomes hard, not amenable to deformation. However, it is a brittle substance that can break on impact. The structure also determines the high thermal conductivity of diamond and the property of its crystals to refract light.

Graphite has a different structure. At the atomic level, it consists of layers located in different planes. Each layer is made up of hexagons adjacent to each other, like honeycombs. The bond between the atoms, which are the vertices of the hexagons, is only strong within each layer. Atoms located in different layers are practically independent of each other.

graphite structure

The pencil mark is easily detachable layers of graphite. The substance, due to its structural features, absorbs light, taking on a rather nondescript appearance (but with a metallic sheen), and has electrical conductivity.

The inherent properties of minerals determine their suitability in a particular area. What is the difference between diamond and graphite regarding their application? Brilliant diamond is ideal for jewelry production. And the hardness of this material makes it possible to make high-quality glass cutters, super-strong drills and other popular products from it.

Graphite rods during the course of many processes play the role of electrodes. Crushed graphite is part of mineral paints and is used as a lubricant. And from a mixture of this substance and clay, special containers are made for melting metals.

Diamond, graphite and coal- consist of homogeneous graphite atoms, but have different crystal lattices.

Brief description: diamond, graphite and coal

Crystal lattices graphite do not have strong bonds, they are separate scales and seem to slide over each other, easily separating from the total mass. Graphite is often used as a lubricant for friction surfaces.

Coal consists of the smallest particles of graphite and the same small particles of carbon, which is in combination with hydrogen, oxygen, nitrogen.

Crystal cell diamond rigid, compact, has high hardness.

For thousands of years, people did not even suspect that these three substances had anything in common. All of these are recent discoveries.

Nature did not give any signs of their relationship. Coal deposits have never coexisted with graphite. Geologists have never found sparkling diamond crystals in their deposits.

But time does not stand still. At the end of the 17th century, Florentine scientists managed to burn the diamond. After that, not even a tiny pile of ash remained. The English chemist Tennant, 100 years later, found that when the same amount of graphite, coal, and diamond are burned, the same amount of carbon dioxide is formed. This experience revealed the truth.

Interconversions of diamond, graphite and coal

Immediately, scientists were interested in the question: is it possible to transform one allotropic form of carbon into another? And the answers to these questions have been found.
It turned out that diamond goes completely into graphite, if it is heated in airless space to a temperature of 1800 degrees.

If through coal miss electricity in a special furnace, it turns into graphite at a temperature of 3500 degrees.

Turning - Graphite or Coal into Diamond

The third was more difficult for people transformation - graphite or coal into diamond. Scientists have been trying to implement it for almost a hundred years.

Get diamond from graphite

The first was apparently Scottish scientist Genney. In 1880 he began a series of his experiments. He knew that the density of graphite was 2.5 grams per cubic centimeter and that of diamond was 3.5 grams per cubic centimeter. This means that it is necessary to condense the stacking of atoms and get diamond from graphite he decided.

He took a strong steel gun barrel, filled it with a mixture of hydrocarbons, firmly closed both holes and glowed to a red heat. Giant, according to the concepts of that time, pressure arose in the red-hot pipes.

More than once it tore apart heavy-duty gun barrels like aerial bombs. But still, some survived the entire cycle of heating. When they cooled, Gennaeus found several dark, very strong crystals in them.

I got fake diamonds

Genney decided.

Method for obtaining artificial diamonds

10 years after Gennaeus French scientist Henri Moisson subjected the carbon-rich cast iron to rapid cooling. Instantly hardened surface crust of it, decreasing in size during cooling, subjected the inner layers to monstrous pressure.

When Moisson then dissolved cast-iron nucleoli in acids, he found tiny opaque crystals in them.

I found another one how to get artificial diamonds!

Decided by the inventor.

The problem of artificial diamonds

After another 30 years, artificial diamond problem began to study English scientist Parsons. At his disposal were the giant presses of the factories he owned. He fired from a cannon directly into the muzzle of another weapon, but he did not manage to get diamonds.

However, already in many developed countries of the world lay in museums artificial diamonds different inventors. And quite a few patents have been issued to obtain them. But in 1943, British physicists subjected the artificially obtained diamonds to a scrupulous check.

And it turned out that all of them have nothing to do with real diamonds, except for Genney diamonds. They turned out to be real. It immediately became a mystery, and remains a mystery today.

Turning graphite into diamond

The advance continued. It was led by a Nobel Prize winner American physicist Percy Bridgman. For almost half a century he was engaged in the improvement of technology beyond high pressures.

And in 1940, when he had presses at his disposal that could create pressure up to 450 thousand atmospheres, he began experiments on turning graphite into diamond.

But he could not make this transformation. Graphite, subjected to monstrous pressure, remained graphite. Bridgman understood what his machine was missing: heat.

Apparently, in the underground laboratories where diamonds were created, high temperature also played a role. He changed the direction of the experiments. He managed to ensure heating of graphite up to 3 thousand degrees and pressure up to 30 thousand atmospheres. It was almost what we now know is necessary for diamond transformation.

But the missing "almost" did not allow Bridgman to achieve success. The honor of creating artificial diamonds did not go to him.

The first artificial diamonds

The first artificial diamonds were received English scientists Bandy, Hall, Strong and Ventropp in 1955. They created a pressure of 100 thousand atmospheres and a temperature of 5000 degrees.

Catalysts were added to graphite - iron, rum, manganese, etc. And yellow-gray opaque crystals of technical artificial diamonds appeared on the border of graphite and catalysts. Well, diamond goes not only for diamonds, it is also used in factories and factories.

However, somewhat later, American scientists found a way to obtain transparent diamond crystals. To do this, the grant is subjected to a pressure of 200,000 atmospheres, and then heated to a temperature of 5,000 degrees by an electric discharge.

The short duration of the discharge - it lasts for thousandths of a second - leaves the installation cold, and the diamonds are clean and transparent.

Creation of artificial diamonds

Soviet scientists came to creation of artificial diamonds in their own way. Soviet physicist O.I. Leipun conducted theoretical studies and established in advance those temperatures and pressures at which diamond transformation of graphite is possible.

These figures in those years - this was in 1939 - seemed amazing, standing beyond the boundaries of what is achievable for modern technology: pressure not less than 50 thousand atmospheres and temperature 2 thousand degrees. And yet, after the stage of theoretical calculations, it was time to create experimental designs, and then industrial plants. And today there are numerous devices that produce artificial diamonds and other, even harder substances. The highest achievement of nature in the hardness of the material has not only been achieved, but has already been blocked.

Such is the history of the discovery of the third transformation of carbon, the most important for modern technology.

How the diamond came into existence

But what remains the most amazing thing about the diamond transformation of carbon? That scientists still do not understand how diamond originated in nature!

It is known that the only primary diamond deposits are kimberlite pipes. These are deep cylindrical wells with a diameter of several hundred meters, filled with blue clay - kimberlite, with which precious stones were brought to the surface of the earth.

Hypothesis of the deep birth of diamonds

The earliest was hypothesis of deep birth of diamonds. According to this hypothesis, sparkling crystals emerged from molten magma at a depth of about 100 kilometers, and then, along with magma, along cracks and faults, slowly rose to the surface.

Well, from a depth of 2-3 kilometers, magma broke through and pulled out to the surface, forming a kimberlite pipe.

Explosive hypothesis

This hypothesis was replaced by another one, which should probably be called explosive hypothesis. She was nominated L. I. Leontiev, A. A. Kademeky, V. S. Trofimov. In their opinion, diamonds occur at a depth of only 4-6 kilometers from the earth's surface.

And the pressure required for the formation of diamonds is created by an explosion caused by some explosives that have penetrated into the cavities occupied by magma from the surrounding sedimentary rocks. It can be oil, bitumen, combustible gases. The authors of the hypothesis proposed several options chemical reactions, as a result of which explosive mixtures are formed and free carbon appears.

This hypothesis explained both the high temperature required for diamond transformation and the gigantic pressure. But she did not explain all the features of kimberlite pipes. It was very easy to prove that the rocks of the kimberlite pipe were formed at a pressure not exceeding 20 thousand atmospheres, but it is impossible to prove that they originated at a higher pressure.

Today, geophysicists have established quite accurately which rocks require certain pressures and temperatures of formation. For example, a constant companion of diamond - the mineral pyrope - requires 20 thousand atmospheres, diamond - 50 thousand. More than for pyrope, and less than for diamond, pressure is required by coesite, stishovite, piezolite.

But neither these nor other rocks that require such high pressures for their formation are found in kimberlite. The only exception here is the diamond. Why is it so? The answer to this question was decided by the doctor of geological and mineralogical sciences E. M. Galymov.

Why, he asked himself, must a pressure of 50,000 atmospheres necessarily be characteristic of the entire mass of magma in which diamonds are created? After all, magma is a stream. Whirlwinds, and rapids, and hydraulic shocks, and bubbles of cavitation occurring in places are possible in it.

Hypothesis of diamond birth in the cavitation mode

Yes exactly cavitation! This is a surprisingly unpleasant phenomenon that brings a lot of trouble to hydraulics! Cavitation can occur on the blades of a hydraulic turbine if it has even slightly gone beyond the boundaries of the calculated regime. The same trouble can befall the hydraulic blades, which have switched to forced mode.

Cavitation can also destroy the blades of a steamship propeller, as if overstrained in the struggle for speed. It destroys, destroys, corrodes. Yes, this is most accurate: it corrodes! Heavy-duty steels, shining with mirror polished surfaces, turn into a loose porous sponge.

It was as if thousands of tiny, merciless and greedy mouths were tearing apart the metal in the place where the cavitation had gnawed it. Yes, even mouths that are "tough" with alloyed metal, from which a file bounces! Quite a few accidents of turbines and pumps, the death of steamships and motor ships occurred due to the presence of cavitation. And a hundred years have not passed, as they figured out what it is - cavitation.

But really, what is it? Imagine a fluid flow moving in a pipe of variable cross section. In places, in constrictions, the flow speed increases, in places, where the flow expands, the flow speed decreases. At the same time, but according to the reverse law, the pressure inside the liquid changes: where the speed increases, the pressure drops sharply, and where the speed decreases, the pressure increases.

This law is obligatory for all moving liquids. It can be imagined that at certain speeds, the pressure drops to the point at which the liquid boils, and vapor bubbles appear in it. From the side it seems that the liquid in the place of cavitation began to boil, it is filled with a white mass of tiny bubbles, it becomes opaque.

It is these bubbles that are the main problem with cavitation. How cavitation bubbles are born and how they die is still not well understood. It is not known whether their inner surfaces are charged. It is not known how the substance of liquid vapor in a bubble behaves. And Galymov was initially unaware of whether cavitation bubbles could even arise in the magma filling the kimberlite pipe.

The scientist made the calculations. It turned out that cavitation is possible at magma flow rates exceeding 300 meters per second. Such speeds are easy to obtain for water, but can heavy, thick, viscous magma flow at the same speed? Again, calculations, calculations and the long-awaited answer: yes, it can! For her, speeds of 500 meters per second are possible.

Further calculations were to find out whether the required values of temperature and pressure would be achieved in the bubbles - 50 thousand atmospheres of pressure and 1500 degrees of temperature. And these calculations gave positive results.

The average pressure in the bubble at the moment of collapse reached a million atmospheres! And the maximum pressure can be ten times greater. The temperature in this bubble has a value of 10 thousand degrees. Needless to say, the conditions have far stepped over the limit for diamond transformation.

Let's say right away that the conditions that a cavitation bubble creates for the birth of a diamond are very peculiar. In addition to the temperatures and pressures that occasionally arise in the tiny volumes of these bubbles, shock waves rush through there, lightning strikes sparkle - electric sparks flare up.

Sounds break out of the narrow section of the liquid covered by cavitation. Connecting, they are perceived as a kind of buzz, similar to that which comes from a boiling kettle. But it is precisely such conditions that are ideal for the emerging diamond crystal. Indeed, his birth takes place in thunder and lightning.

It is possible to imagine in a simplified way and omitting many details what is happening inside the cavitation bubble. Here the fluid pressure has increased, and the cavitation bubble begins to disappear. They moved to the center of its walls, and shock waves immediately break away from them. They move in the same direction towards the center.

Do not forget about their features. Firstly, they move at supersonic speeds, and secondly, it leaves behind an extremely excited gas, in which both pressure and temperature have risen sharply.

Yes, this is the same shock wave that moves along a piece of burning roof and turns peaceful burning into a furious, all-destroying explosion. At the center of the bubble, shock waves traveling from different parties, converge. In this case, the density of the substance at this point of convergence exceeds the density of diamond.

It is difficult to say what form the substance acquires there, but it begins to expand. At the same time, he has to overcome the back pressure, measured in millions of atmospheres. Due to this expansion, the substance found in the center of the bubble is cooled from tens of thousands of degrees to only a thousand degrees.

Introduction

The diamond industry of our country is at the stage of development, the introduction of new technologies for processing minerals.

Found deposits of diamonds are opened only by erosion processes. For the scout, this means that there are many "blind" deposits that do not come to the surface. You can learn about their presence by the detected local magnetic anomalies, the upper edge of which is located at a depth of hundreds, and if you're lucky, then tens of meters. (A. Portnov).

Based on the foregoing, I can judge the prospects for the development of the diamond industry. That is why I chose the topic - "Diamond and Graphite: Properties, Origin and Significance".

In my work, I tried to analyze the relationship between graphite and diamond. To do this, I compared these substances from several points of view. I considered general characteristics minerals, industrial types of their deposits, natural and technical types, development of deposits, areas of application, the value of these minerals.

Despite the fact that graphite and diamond are polar in their properties, they are polymorphic modifications of the same chemical element - carbon. Polymorphic modifications, or polymorphs, are substances that have the same chemical composition but different crystal structure. With the beginning of the synthesis of artificial diamonds, interest in the study and search for polymorphic modifications of carbon has sharply increased. At present, in addition to diamond and graphite, lonsdaleite and chaotite can be considered reliably established. The first one was found in all cases only in close intergrowth with diamond and therefore is also called hexagonal diamond, and the second one occurs in the form of plates alternating with graphite, but located perpendicular to its plane.

Polymorphic modifications of carbon: diamond and graphite

The only mineral-forming element of diamond and graphite is carbon. Carbon (C) is a chemical element of the IV group of the periodic system of chemical elements of D.I. Mendeleev, atomic number - 6, relative atomic mass - 12.011 (1). Carbon is stable in acids and alkalis, it is oxidized only with potassium or sodium dichromate, ferric chloride or aluminum. Carbon has two stable isotopes, C(99.89%) and C(0.11%). Data on the isotopic composition of carbon show that it can be of different origins: biogenic, non-biogenic, and meteoric. The variety of carbon compounds, due to the ability of its atoms to combine with each other and atoms of other elements different ways, determines the special position of carbon among other elements.

General characteristics of a diamond

When the word "diamond" is immediately remembered secret stories about the search for treasure. Once upon a time, people who hunted for diamonds did not even suspect that the object of their passion was crystalline carbon, which forms soot, soot and coal. This was first proved by Lavoisier. He set up an experiment on burning a diamond, using an incendiary machine assembled specifically for this purpose. It turned out that diamond burns in air at a temperature of about 850-1000 * C, leaving no solid residue, like ordinary coal, and burns in a stream of pure oxygen at a temperature of 720-800 * C. When heated to 2000-3000 * C without access to oxygen, it turns into graphite (this is due to the fact that the homeopolar bonds between carbon atoms in diamond are very strong, which leads to a very high melting point.

Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly.

Carbon atoms in diamond are in a state of sp3 hybridization. In the excited state, the valence electrons in carbon atoms are depaired and four unpaired electrons are formed.

Each carbon atom in diamond is surrounded by four others located from it in the direction from the center at the vertices of the tetrahedron.

The distance between atoms in tetrahedra is 0.154 nm.

The strength of all bonds is the same.

The entire crystal is a single three-dimensional framework.

At 20*C, the density of diamond is 3.1515 g/cm. This explains its exceptional hardness, which is different along the faces and decreases in the sequence: octahedron - rhombic dodecahedron - cube. At the same time, diamond has perfect cleavage (according to the octahedron), and its bending and compressive strength is lower than that of other materials, so diamond is brittle, splits upon a sharp impact, and turns into powder relatively easily when crushed. Diamond has the highest hardness. The combination of these two properties allows it to be used for abrasive and other tools operating at a significant specific pressure.

The refractive index (2.42) and dispersion (0.063) of diamond far exceed those of other transparent minerals, which, combined with maximum hardness, determines its quality as a precious stone.

Impurities of nitrogen, oxygen, sodium, magnesium, aluminum, silicon, iron, copper and others were found in diamonds, usually in thousandths of a percent.

Diamond is extremely resistant to acids and alkalis, is not wetted by water, but has the ability to adhere to certain fatty mixtures.

Diamonds occur in nature both in the form of well-defined individual crystals and polycrystalline aggregates. Correctly formed crystals look like polyhedrons with flat faces: an octahedron, a rhombic dodecahedron, a cube, and combinations of these shapes. Very often, there are numerous stages of growth and dissolution on the faces of diamonds; if they are indistinguishable to the eye, the faces appear curved, spherical, octahedroid, hexahedroid, cuboid, and combinations thereof. different shape crystals is due to their internal structure, the presence and nature of the distribution of defects, as well as the physicochemical interaction with the environment surrounding the crystal.

Among the polycrystalline formations stand out - ballas, carbonado and board.

Ballas are spherulite formations with a radially radiant structure. Carbonado - cryptocrystalline aggregates with a size of individual crystals of 0.5-50 microns. The board is clear-grained aggregates. Ballas and especially carbonado have the highest hardness of all types of diamonds.

Fig.1

Fig.2

General characteristics of graphite

Graphite is a gray-black crystalline substance with a metallic sheen, greasy to the touch, inferior in hardness even to paper.

The structure of graphite is layered, inside the layer the atoms are connected by mixed ionic-covalent bonds, and between the layers by essentially metallic bonds.

Carbon atoms in graphite crystals are in sp2 hybridization. The angles between the bond directions are 120*. The result is a grid consisting of regular hexagons.

When heated without access to air, graphite does not undergo any change up to 3700 * C. At the specified temperature, it is expelled without melting.

Graphite crystals are usually thin plates.

Due to the low hardness and very perfect cleavage, graphite easily leaves a mark on paper, greasy to the touch. These properties of graphite are due to weak bonds between the atomic layers. The strength characteristics of these bonds characterize the low specific heat capacity of graphite and its high melting point. As a result, graphite has an extremely high refractoriness. In addition, it conducts electricity and heat well, is resistant to many acids and other chemicals, mixes easily with other substances, has a low coefficient of friction, and high lubricity and hiding power. All this led to unique combination in one mineral of important properties. Therefore, graphite is widely used in industry.

The carbon content in the mineral aggregate and the graphite structure are the main features that determine the quality. Graphite is often referred to as a material that, as a rule, is not only monocrystalline, but also monomineral. Basically, they mean aggregate forms of graphite substance, graphite and graphite-containing rocks and enrichment products. In addition to graphite, they always contain impurities (silicates, quartz, pyrite, etc.). The properties of such graphite materials depend not only on the content of graphite carbon, but also on the size, shape and mutual relations of graphite crystals, i.e. from the textural and structural features of the material used. Therefore, to assess the properties of graphite materials, it is necessary to take into account both the features of the crystal structure of graphite and the textural and structural features of their other components.

Fig.3.