Graphite- mineral, hexagonal crystalline polymorphic (allotropic) modification of pure carbon, the most stable under conditions crust... Other modifications: diamond, lonsdaleite, chaoite. The layers of the crystal lattice can be located in different ways relative to each other, forming a number of polytypes, with symmetry from hexagonal system (dihexagonal-dipyramidal type of symmetry) to trigonal (di-trigonal-scalenohedral w.c.). The crystal lattice of graphite is of a layered type. In the layers, C atoms are located at the nodes of the hexagonal cells of the layer. Each C atom is surrounded by three neighbors with a distance of 1.42Α.
Graphite does not dissolve in acids. Greasy to the touch. Flexible. Natural graphite contains 10-12% of impurities of clays and iron oxides.
Forms of finding
Well-formed crystals are rare. Crystals are lamellar, scaly, curved, usually lamellar imperfect form... More often it is represented by leaves without crystallographic outlines and their aggregates. Forms continuous cryptocrystalline, leafy or rounded radial-radial aggregates, less often - spherulite aggregates of concentric-zonal structure. In coarse-crystalline precipitates, triangular hatching is often observed on the (0001) planes.
Origin
Formed at high temperatures in volcanic and igneous rocks, in pegmatites and skarns. It occurs in quartz veins with wolframite and other minerals in medium-temperature hydrothermal polymetallic deposits. Widespread in metamorphic rocks- crystalline schists, gneisses, marbles. Large deposits are formed as a result of coal pyrolysis under the influence of traps on coal deposits (Tunguska basin). Accessory mineral of meteorites.
Mineral properties
- Origin of name: from Greek γράφω - I write
- Opening year: known since antiquity
- Electrical properties of the mineral: Conducts well electricity
- Thermal properties: Does not melt (burns out at 3500 ° C)
- IMA status: valid, described for the first time before 1959 (before IMA)
- Strunz (8th edition): 1 / B.02-10
- Hey "s CIM Ref .: 1.25
- Dana (7th Edition): 1.3.5.2
- Dana (8th edition): 1.3.6.2
- Molecular weight: 12.01
- Cell parameters: a = 2.463Å, c = 6.714Å
- Attitude: a: c = 1: 2.726
- The number of formula units (Z): 4
- Unit cell volume: V 35.27 ų
- Twinning: by (1121)
- Point group: 6 / mmm (6 / m 2 / m 2 / m) - Dihexagonal Dipyramidal
- Space group: P63mc
- Density (calculated): 2.26
- Density (measured): 2.09 - 2.23
- Specific gravity: 2,1 - 2,3
- Pleochroism: strong
- Type of: uniaxial (-)
- Optical Anisotropy: extraordinary
- Reflected light color: iron black turning into steel gray
- Allocation form: Leafy, scaly, radial-radiant, earthy aggregates
- Classes on the taxonomy of the USSR: Nonmetals
- IMA classes: Native elements
- Chemical formula: C
- Systema: hexagonal
- Colour: Iron black, dark steel gray
- Feature color: Black, shiny
- Shine: metallic matt semi-metallic
- Transparency: opaque
- Cleavage: very perfect by (0001)
- Kink: mica-like
- Hardness: 1 1,5 2
- Microhardness: VHN10 = 7 - 11
- Literature: Lobzova R.V. Graphite and alkaline rocks of the Botogol massif region. M., 1975.124 p.
Mineral photo
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Mineral deposits Graphite
- Irkutsk region
- Olkhon region
- Russia
- Botogolsk graphite deposit
- Sri Lanka
Graphite is a mineral used in the most different areas industry. This popularity is due to its unique properties (softness, easy machining, high electrical conductivity, chemical inertness).
Exists artificial species of this material, which are also highly demanded. They are used not only in various industries, but also for carrying out microscopic examinations(as calibration material).
Application of artificial graphite
Used in the following industrial sectors:
- Mechanical engineering;
- Atomic engineering;
- Metallurgy;
- Electrical engineering manufacturing;
- Chemical industry.
Varieties of artificial graphite impregnated with various synthetic resins are often used. They are used to create chemical equipment, are indispensable in the manufacture of shut-off or connecting fittings.
Artificial graphite is also made of:
- Mechanical seals;
- Bearings;
- Reactor buildings;
- Lining tiles.
Using natural graphite
This mineral has the widest range of applications and is indispensable in a wide variety of industrial sectors.
Where is graphite used:
- Mechanical engineering;
- Chemical industry;
- Metallurgy;
- Production building materials- this mineral serves as one of the irreplaceable components in the production of bricks, in particular, refractory bricks;
- Atomic energy - it is used as a moderator of neurons;
- Production electrical appliances- for the manufacture of electrical contacts, as well as electrodes;
- Medicine.
The use of graphite in metallurgy:
- In this area, graphite is used to make molds for alloys, refractory ladles, as well as containers in which crystallization takes place;
- Melting crucibles are made from it;
- Graphite can be used to saturate metals with carbon (i.e. carbonate), as well as create reactive metals;
- Graphite powder is often used as a lubricant for casting molds.
Mechanical engineering: what is graphite used for
In this industry, the use of the mineral is also very diverse. Its properties make graphite indispensable for the creation of a wide variety of products.
In mechanical engineering, graphite is used to produce:
- Lining plates;
- Electrodes (graphite);
- Various heating elements;
- Powders and pastes for sealing contacts, for example, in butt clearances;
- Sliding contacts (electric brushes);
- Bearings, sealing rings;
- Electrostatic coatings.
Graphite in the chemical industry:
- A variety of lubricants are produced from this mineral, which are used both in production and in everyday life;
- Is a filler for some types of plastics;
- It is used for the synthesis of artificial diamonds;
- Indispensable in the manufacture of paints that have excellent anti-corrosion properties, as well as various varnishes;
- Used as a filler for technological mixtures;
- Can serve as a plasticizer;
- Is one of the components of glue for bonding rubberized fabrics;
- Part of additives and antifriction fillers (for transmission or engine oils), coolants;
- It is used for the manufacture of alkaline batteries.
Graphite: medical applications
This mineral is part of many medicines(primarily homeopathic). It is used for dermatological diseases, as well as for the formation of scars or adhesions, metabolic disorders.
Pencils are also made from black graphite.
The word graphite in translation from Greek means "I write". A mineral with this name is naturally formed at high temperatures in volcanic rocks.
Graphite characteristics
Graphite is a representative of the class of high strength native elements. Its structure has big amount layers.
There are two types of graphite in nature:
- coarse crystalline,
- fine crystalline.
By the size of the crystals and by their location relative to each other, the following types of graphite are found in nature:
- explicit crystalline,
- cryptocrystalline.
Graphite has a fairly layered structure. Each of the layers has a wavy shape. It is mild.
Graphite is one of the elements that consists mainly of crystals different sizes... They have a plastic structure and small scales at the edges. In terms of their strength, they can be compared to diamonds.
The crystal lattice of graphite consists of a large number of layers, which have a different arrangement relative to each other.
Today, artificial graphite is often produced, which is created from a mixture various substances... It is used in various branches of human life. Artificial graphite has a large number of types.
V modern world it is planned to extract gold from graphite. Scientists have found that one ton of graphite contains approximately 18 grams of gold. This amount of gold ore is inherent in gold deposits. Currently, it is possible to obtain gold from graphite not only in our country, but also in other countries of the world.
Physical properties of graphite
One of the main properties of graphite is its ability to conduct electric current. Its physical properties differ from the parameters of a diamond in that it does not have the same high level hardness. Its structure is initially rather soft. However, after heating, it becomes hard and brittle. The material starts to crumble.
The physical properties of graphite are as follows:
- does not dissolve in acid.
- melting graphite at temperatures below 3800 degrees Celsius is impossible.
- after heating it acquires a hard and brittle structure.
These are far from all the properties of graphite. There are also parameters that make this item unique.
Graphite has the following characteristics:
- the melting point of graphite is 3890 degrees Celsius,
- the color of graphite is dark gray with a metallic sheen,
- the heat capacity of graphite is 0.720 kJ
- the resistivity of graphite is 800,000 · 10−8 (Ohm · Meter).
Attention: The only parameter of all the characteristics of graphite, which depends on the type of element, is the thermal conductivity of graphite. It is 278.4 to 2435 W / (m * K).
Table. Physical properties of graphite.
| Thermal conductivity coefficient λ, W / (m ° С) graphite: | ||||||
| - crystalline | || | 354,7 | 308,2 | |||
| - natural | _|_ | 195,4 | 144,2 | 112,8 | 91,9 | 75,6 |
| - pressed | || | 157 | 118,6 | 93,0 | 69,8 | 63,9 |
| - artificial with p = 1.76 g / cm3 | _|_ | 104,7 | 81,4 | 69,8 | 58,2 | |
| - the same, with p = 1.55 g / cm3 | || | 130,3 | 102,3 | 79,1 | 63,9 | 53,5 |
| Tear strength σпц, MN / m2 | || | 14,2 | 15,2 | 15,9 | 16,5 | 17,6 |
| _|_ | 10,3 | 11,3 | 12,0 | 12,5 | 13,7 | |
| Elastic modulus E, MN / m2 | || | 5880 | 7100 | 7350 | 7500 | 7840 |
| _|_ | 2700 | 3040 | 3200 | 3630 | 3920 | |
| Specific heat s, kJ / (kg0C) | 0,71 | 1,17 | 1,47 | 1,68 | 1,88 | |
| Electrical resistance pe104, Omsm | 16 | 13 | 11 | 10 | 9 | |
| Linear expansion coefficient α 106, 1 / ° С | || | 7,2*1 | 8,5*2 | 10,0*3 | 13,0*4 | |
| _|_ | 4,0*1 | 5,5*2 | 6,8*3 | 9,3*4 | ||
| || | 1,8*1 | 1,55*2 | 1,45*3 | 1,40*4 |
Extraction of graphite
The extraction of graphite is a complex process. For this, a large number of types of equipment have been created. It is used to mine and crush an element. Graphite deposits are usually found deep underground. It is for this reason that drilling rigs are most often used, which make it possible to get to the field of this element.
Graphite Applications
As you know, such a material as graphite has a large number of unique qualities. They determine the scope of its application. Thanks to. that this material is resistant to high temperatures; it is used for the production of lining plates.
The use of graphite is also used in the nuclear industry. There he plays important role when slowing down neutrons.
Getting diamond from graphite is also possible. In the modern world, it is possible to obtain synthetic diamonds, which, in terms of their qualities and outward appearance will resemble natural material.
Pyrolytic graphite is a special form of an element such as graphite. This variety has found wide application in the field of microscopic research. It is used as a calibration material.
Graphite. Properties, application
It is most commonly used in scanning tunneling microscopy and atomic force microscopy. This type of graphite is classified as synthetic. It can be obtained by heating coke and pitch.
Thanks to graphite, active metals can be obtained from a chemical point of view by electrolysis. This method the use of the element is explained by the fact that graphite has a fairly good electrical conductivity.
In the production of plastic products, graphite has also found its use. It is used to fill plastics.
The most known method the use of graphite is the production of rods for conventional simple pencils that people are so used to.
What is graphite? Formula, properties and applications of graphite
Graphite. Properties, application
Graphites are gray-colored substances with a metallic luster, amorphous, crystalline, or fibrous constitution, oily to the touch, specific gravity from 1.9 to 2.6.
In appearance, graphite has a metallic lead-gray color, ranging from silvery to black, with a characteristic oily sheen.
Therefore, consumers often call explicit crystalline graphites silvery, and cryptocrystalline graphites black.
Depending on the structural structure, graphites are divided into:
explicit crystalline,
cryptocrystalline,
graphitoids,
Graphite mine. Photo: born1945
The crystal lattice of graphite consists only of carbon atoms. The crystal lattice of graphite is characterized by a pronounced layered structure, the distance between the layers is 0.335 nm. In the crystal lattice of graphite, each carbon atom is bonded to three other surrounding carbon atoms. The crystal lattice of graphite is of two types: hexagonal (α-graphite) and rhombohedral (β-graphite, metastable form). The carbon atoms of each layer of the crystal lattice of α-graphite are located opposite the centers of the hexagons located in the adjacent (lower and upper) layers; the position of the layers is repeated through one, each layer is shifted relative to the other in the horizontal direction by 0.1418 nm (ABABA packing). In the rhombohedral lattice of β-graphite, the position of the planar layers is repeated not through one layer, as in the hexagonal lattice, but through two. Despite the fact that β-graphite is metastable, in natural graphite its content can reach up to 30%. At temperatures of 2230-3030 ° C, rhombohedral graphite completely transforms into hexagonal. Alpha graphite and beta graphite have similar physical properties (with the exception of a slightly different graphene structure).
The electrical conductivity of graphite crystals is anisotropic: it is close to metallic in the direction parallel to the basal plane, and an order of magnitude less in the perpendicular direction. Anisotropy is also characteristic of sound transmission ( acoustic properties) and the heat-conducting properties of graphite.
Graphite properties
The widespread use of graphite is based on several unique properties:
- good electrical conductivity;
- resistance to aggressive environments;
- resistance to high temperatures;
- high lubricity.
Electrical properties
The electrical conductivity of graphite is 2.5 times that of mercury. At a temperature of 0 degrees. electrical resistivity ranges from 0.390 to 0.602 ohms. Low limit resistivity for all types of graphite is the same and equal to 0.0075 ohm.
Thermal properties
The melting point of graphite is 3845-3890 C at a pressure from 1 to 0.9 atm.
Magnetic properties
Levitation of graphite. Photo: yellowcloud
Solubility of graphite
Elasticity of graphite
Optical properties
Graphite Applications
Natural graphites are used in many technological and production processes: refractories (high-quality, graphite-magnesium, aluminum-graphite), foundry, brake linings, lubricants, pencil production, crucibles, galvanic batteries, alkaline batteries, powder metallurgy, carbon-graphite materials (electric brushes, electric coal products, antifriction materials), steel production, thermally expanded graphite, other areas (dyes and polishes), anti-carbon materials, parts for electrical engineering, magnetic tapes, industrial diamond production, cooling and lubricating suspensions).
Artificial crushed graphites - intended for the carburization of cast iron and steel in open-hearth, oxygen-converter and electric steelmaking processes when smelting steel with a reduced proportion of pig iron in the charge, for foaming slags in metallurgical processes, in the manufacture of carbon-graphite materials and products, as a filler for graphite-plastics and as independent products in other consuming industries.
The domestic industry produces a large assortment of graphite electric brushes for various electric machines, electric lighting coals for projectors and for demonstration and filming of films, elemental - galvanic batteries, welding and for spectral analysis, products for electrovacuum and communication technology.
Graphite serves as a highly refractory lean additive in ceramic masses. It imparts high refractoriness, thermal conductivity and thermal stability to the crucible mass, gives crucibles a smooth surface to which the molten metal does not adhere well. It restores when high temperatures metal oxides and prevents metal oxidation.
Of greatest importance is the production of graphite melting crucibles, as well as lids for them. In addition, extensions and supports for crucibles, crucibles for special furnaces, and retorts are made of graphite. Soldering baths, pencil rod firing baths, graphite-carborundum muffles and other products. Crystalline graphite is used as a highly refractory material in the manufacture of high-quality highly refractory facing products for masonry of blast furnaces, furnaces, and steam boilers.
Dissolution - graphite
Page 1
Dissolution of graphite in the y-phase is an important process during normalization (as well as during hardening) of cast iron with a ferritic or ferrite-pearlite structure. This process is similar to carburizing steel; the difference is that during carburizing, the surface layer of the steel part is saturated with carbon from external environment, and when the cast iron is heated, the numerous inclusions of graphite located in the metal base are the carburizing agent, and saturation with carbon occurs throughout the entire volume of the casting. The dissolution of carbon in the austenite of cast iron is affected by temperature: with an increase in the heating temperature, the solubility of carbon in the y-phase increases sharply. As a result of normalization of cast iron with the original structure of the bulk of ferrite or ferrite and pearlite, a structure of pearlite or sorbitol-like pearlite with increased hardness and strength is obtained.
The dissolution of graphite occurs rather quickly only at high temperatures.
As the graphite dissolves at the cold contact and the carbon concentration in the melt increases, the zone where SG (TX) CA (TX) expands towards higher temperatures and lower supersaturations.
Thermodynamic data for the dissolution of graphite are still scarce and often contradictory. The question of the enthalpy of the process is not entirely clear.
When heated, the graphite dissolves in austenite, and therefore, despite the different initial structure of cast iron, austenite with a eutectoid or hypereutectoid carbon concentration undergoes transformation during cooling.
The pores formed during the dissolution of graphite and decarburization of cast iron are partially or completely filled with oxides. Along with iron, silicon and manganese are oxidized, forming stable compounds with oxygen. As well as on the surface, the oxidized layer in the bulk of the castings has a heterogeneous structure.
The possibility of pore formation upon dissolution of graphite follows from the data of dilatometric analysis. If the process of dissolution of graphite were reversible, the dimensions of the samples during the precipitation and dissolution of graphite would change by the same value, but opposite in sign.
It was found that when graphite dissolves in liquid iron, the value of D) / s has positive value over the entire range of concentrations and at NG 0 1 is close to 5000 cal / mol. The change in the DL entropy c exceeds the values corresponding to ideal solutions; with an increase in the carbon concentration, the actual values of DL c decrease faster than the corresponding values corresponding to ideal solutions.
Thus, the main mechanism for the dissolution of graphite is, apparently, direct contact diffusion. In this case, the carburization of iron can be the result of diffusion of carbon over the surface of the pore to those areas where contact with the matrix is retained, and further by means of boundary and bulk diffusion. A large difference in carburization along the contour of the inclusion is not observed, which can be realized if surface diffusion significantly prevails over volume diffusion. In many diffusion vapors, such a ratio of the diffusion rates actually takes place; however, it is not known to what extent this may be true for Fe - Si - C alloys.
Based on the microscopic picture of graphite dissolution considered above, it is easy to explain the effect of the austenitization temperature and surface-active impurities. When heated, the solubility of carbon in austenite increases, so that a decrease in the cohesion of graphite is accompanied by an increase in the adhesion of graphite to the matrix. As a result, the restoration of the contact between the two phases by destruction of graphite occurs more often. Simultaneously with heating, the role of gases also increases. Addition of elements to cast iron that reduce surface tension matrix, and thus weakening adhesion, should prevent carburization. Dissolution can also be delayed by impurities that increase the binding forces in the basal planes of graphite.
Graphite properties
The second type of interaction takes place when graphite or diamond is dissolved in liquid metals. Under these conditions, the wetting of graphite is less intense than in the first case.
The second way is to use the thermodynamic characteristics of the processes associated with the dissolution of graphite in liquid iron.
Pages: 1 2 3 4
GRAPHITE (from the Greek grapho - I write * a. Graphite, black lead, plumbago; n. Graphit; f. Graphite; and. Grafito) is a mineral of the class of native elements, one of the polymorphic modifications of carbon, thermodynamically stable under the conditions of the earth's crust. Impurities of gases (CO2, CO, H, CH4), sometimes water, bitumen, as well as Si, Al, Mg, Ca, etc. It crystallizes in a hexagonal system. The structure is layered. Well-formed crystals are rare; they look like hexagonal tablets with a well-developed basopinacoid face. Twins are noted. Usually forms scaly, columnar, massive, kidney-shaped, spherulite, spherulite-like and cylindrical zonal aggregates.
Graphite properties
Natural graphites are distinguished by the size of the crystals and their mutual arrangement into explicit crystalline and cryptocrystalline.
The use of graphite in various industrial sectors
The size of the former exceeds 1 micron, the second is less than 1 micron. In industry, coarse-crystalline (over 50 microns), fine-crystalline (less than 50 microns) and fine-crystalline (less than 10 microns) graphites are distinguished by the size of crystals. Pinacoid cleavage is very perfect. The line is dark gray to black. Greasy to the touch, stains hands. Metallic luster. Anisotropic. Mineralogical hardness 1-2. Density 2250 kg / m3. Refractory - does not melt at normal pressure, the sublimation temperature is above 4000 K. Electrically conductive - the electrical resistance of crystals is 0.42.10-4 Ohm / m, for fine powders - 8-20.10-2 Ohm / m. Chemically resistant. Also characteristic are low modulus of elasticity, high specific heat capacity, good resistance to thermal shock, corrosion resistance, high moderating ability of neutrons and small cross-section of their capture. By origin - metamorphic, magmatic. Industrial accumulations are associated mainly with metamorphic deposits. Magmatic deposits are rare and confined to alkaline and ultrabasic rocks. The material composition of ores depends on the genesis. Silicate minerals (quartz, feldspar, mica, clay minerals) are usually present. In marbles, carbonates are usually associated with graphite. Nepheline, wollastonite and kaolinite can be mined as associated minerals. There are three types of graphite ores: flaky, dense crystalline, cryptocrystalline.
Graphite deposit
Deposits of flaky graphite are localized in gneisses, quartzites, and marbles. Formed during the metamorphism of ancient sedimentary strata. The form of deposits is stratus and lenticular, consistent in thickness and length. Graphite flakes form scattered disseminations in the rock. The carbon content in the ore is on average 3-18%. Deposits of graphite are known in the CCCP (for example, Taiginskoe, Ural; Zaval'evskoe, Ukrainian SSR), Austria, Czechoslovakia, Germany, India, Madagascar (Fanandran region), Brazil, KHP, Canada.
Dense crystalline graphite composes veins and lenses in deposits of hydrothermal-pneumalite genesis or nests, lenses and dissemination in contact-reaction deposits. Pneumatolytic-hydrothermal deposits are associated with concordant, less often intersecting pegmatite, quartz, feldspar and calcite veins. Contact-reaction deposits are confined to the contact zones of carbon-rich carbonate and shale rocks with alkaline and gabbroid rocks, less often granites. The ores are composed of feldspar, quartz, less often micas, carbonate; in skarn zones, they are enriched with garnet, wollastonite, pyroxene, scapolite, as well as minerals of alkaline and gabbroid rocks (nepheline, cancrinite, sodalite, sphene, apatite). Graphite (from coarse to fine crystalline) composes flaky and fibrous aggregates. The content in ores is 15-40%, in some deposits 60-90%. It is usually mined underground. The known deposits are Bogala (Sri Lanka) and Botogolskoe (CCCP).
Cryptocrystalline graphite has an imperfect texture and often contains an admixture of a finely dispersed carbonaceous substance. Forms powerful and extended bed-like deposits, sometimes turning into coals. The carbon content is 80-90%. The main rock-forming minerals are quartz, feldspar, sericite, chlorite, and calcite. Graphite is formed during the metamorphism of coals, carbonaceous and bituminous shales near intrusions. The deposits are developed by open-pit and underground methods. The main deposits are located in Mexico (Sonora state), South Kopee, Austria (Kaisersberg mine), CCCP (Noginskoe deposit).
Obtaining graphite
The main method of beneficiation of cryptocrystalline ores is ore picking, of dense crystalline and flake ores - flotation. The quality of concentrates is subject to restrictions on ash content and particle size distribution (graphite flakes are valued in size). Cryptocrystalline ores are ground. In the flotation of flaky and dense crystalline ores, collectors are used - kerosene and other hydrocarbons; foaming agents - pine oil, alcohol; regulators - soda, alkali; depressants - starch, dextrin-based reagents. To improve the selection, liquid glass is fed. The flotation is followed by wet classification, drying, air classification, and hydrometallurgical operations, including soda baking, cinder boiling, sulfuric acid leaching, washing, boiling in soda solution, washing, drying and dry magnetic separation to obtain graphite in a non-magnetic product. When finishing flake blast furnace graphite, electrical separation is used.
Stocks and use
World reserves of graphite (1978, thousand tons) in capitalist and developing countries: scaly - South America, 136; Europe, 3500; Africa, 5442; Asia, 900; dense crystalline - Asia, 2900; cryptocrystalline - North America(without US), 3084; Europe, 5623; Asia, 6168. For the extraction of graphite see Art. graphite industry.
Along with natural, artificial graphite is used, which is obtained by cooling alloys supersaturated with carbon, thermal decomposition of gaseous hydrocarbons, heating anthracite, petroleum coke, coal tar pitch. Graphites are used in metallurgy (crucibles, casting molds, non-stick paints), in chemical engineering (lining material, pipes, etc.), in the production of collectors for dynamos, electrodes, conductive powders, lubricants, antifriction products, in nuclear technology, in the production of pencils, paints, thermal insulation materials. Artificial lumpy graphite is used as erosion-resistant coatings for nozzles rocket engines, combustion chambers of nose cones.
Basic properties of natural graphite
Graphite- Substances of gray color with a metallic luster, amorphous, crystalline, or fibrous constitution, greasy to the touch, specific gravity from 1.9 to 2.6. In appearance, graphite has a metallic lead-gray color, ranging from silvery to black, with a characteristic oily sheen.
Therefore, consumers often call explicit crystalline graphites silvery, and cryptocrystalline graphites black.
Graphite is greasy to the touch and gets dirty very well. On surfaces, it easily gives a dash from silvery to black, shiny. Graphite is distinguished by its ability to adhere to solid surfaces, which makes it possible to create thin films when rubbing the surfaces of solid bodies with it.
Graphite is an alotropic form of carbon, which is characterized by a specific crystal structure that has a peculiar structure.
Depending on the structural structure, graphites are divided into:
- explicit crystalline,
- cryptocrystalline,
- graphitoids,
- highly dispersed graphite materials commonly referred to as coals.
In turn, explicitly crystalline graphites are divided according to the size and structure of crystals into: - dense crystalline (Bogotolskoe graphite deposit),
- flaky (Taiginskoye graphite deposit).
In flaky graphites, crystals are in the form of plates or leaflets. Their scales are greasy, plastic and have a metallic sheen.
The most important properties of graphite
Electrical properties
The electrical conductivity of graphite is 2.5 times that of mercury. At a temperature of 0 degrees.
Graphite - description of graphite, properties, extraction, application, production
electrical resistivity ranges from 0.390 to 0.602 ohms. The low limit of resistivity for all types of graphite is the same and equal to 0.0075 ohm.
Thermal properties
Graphite has a high thermal conductivity, which equals 3.55W * deg / cm and takes place between palladium and platinum.
The thermal conductivity coefficient is 0.041 (5 times more than that of a brick). Thin graphite filaments have a higher thermal conductivity than copper ones.
The melting point of graphite is 3845-3890 C at a pressure from 1 to 0.9 atm.
The boiling point reaches 4200 C.
The ignition temperature in an oxygen jet is 700-730C for explicit crystalline graphites. The amount of heat obtained by burning graphite ranges from 7832 to 7856 kcal.
Magnetic properties
Graphite is considered to be diamagnetic.
Solubility of graphite
Chemically inert and does not dissolve in any solvents other than molten metals, especially those with high point melting. Dissolution produces carbides, the most important properties of which are tungsten, titanium, iron, calcium and boron carbides.
At ordinary temperatures, graphite is very difficult to combine with other substances, but at high temperatures it gives chemical compounds with many elements.
Elasticity of graphite
Graphite is not elastic, but it can be cut and bent nonetheless. The graphite wire is easily bent and twisted into a spiral, and when rolled gives an elongation of about 10%. The tensile strength of such a wire is 2 kg / mm2, and the bending modulus is 836 kg / mm2.
Optical properties
The light absorption coefficient of graphite is constant for the entire spectrum and does not depend on the radiation temperature of the body; for thin graphite filaments, it is 0.77, with an increase in graphite crystals, light absorption is already in the range of 0.52-0.55.
The fat content and plasticity of graphite are the most important properties that make it possible to widely use it in industry. The higher the fat content of the graphite, the lower the coefficient of friction. The fat content of graphite determines its use as a lubricant, as well as its ability to adhere to hard surfaces.
Thanks to these properties, it is possible to create thin films when graphite is rubbed onto the surface of solids.
Low coefficient thermal expansion graphite and the associated high resistance to temperature stresses is a decisive factor in its use as an important and irreplaceable auxiliary material in the metalworking, iron foundry and steel industries, i.e. wherever work surfaces must be protected from direct exposure to molten metal. An important advantage in this use is also its non-wettability, fully reduced metals and neutral slags, strength at high temperatures. The use of graphite for casting parts improves the quality of castings, reduces the amount of rejects, and prevents the formation of burn-in, which requires great effort and expense to remove.
Raw molds and cores are coated with a layer of dry graphite powder. Pure graphite has a low neutron absorption coefficient and the highest moderation coefficient, making it irreplaceable in nuclear reactors... The development of black and color is unthinkable without graphite electrodes, chemical industry.
Graphite is an excellent lining material for electrolytic cells for aluminum production. Carbon-containing materials are used for the construction of electric furnaces and other heating units.
Crucibles and boats are made from graphite for the production of superhard alloys.
In the chemical industry, graphite materials are indispensable for the production of heat exchangers operating in corrosive environments.
And also for the manufacture of heaters, condensers, evaporators, refrigerators, scrubbers, distillation columns, nozzles, nozzles, taps, pump parts, filters.
The domestic industry produces a large assortment of graphite electric brushes for various electric machines, electric lighting coals for projectors and for demonstration and filming of films, elemental - galvanic batteries, welding and spectral analysis, products for vacuum and communication technology.
In mechanical engineering, graphite is used as an antifriction material for bearings, friction rings, end and piston seals, and thrust bearings.
Minerals and rocks/ Description of the mineral Graphite
The table shows the physical properties of graphite in the temperature range from 20 to 800 ° C.
Properties are indicated in a direction both parallel and perpendicular to the major axis of the graphite crystals.
The thermal conductivity of graphite is indicated for the following types: crystalline, natural, pressed artificial. The table shows that the thermal conductivity of graphite decreases with an increase in its temperature.
The specific (mass) heat capacity of carbon at room temperature is 710 J / (kg · deg) and increases with heating. The density of carbon is in the range from 1400 to 1750 kg / m 3.
Given the following physical properties of graphite different density:
- thermal conductivity of graphite, W / (m · deg);
- tear resistance, MN / m 2;
- modulus of elasticity of graphite, MN / m 2;
- specific (mass) heat capacity, kJ / (kg · deg);
- specific electrical resistance, Ohm · m;
- coefficient of thermal linear expansion (KTlR), 1 / deg.
Properties of carbon (graphite) depending on temperature
The table shows the thermophysical properties of carbon (graphite) depending on temperature.
The properties of carbon in the table are indicated at temperatures from 100 to 2000K in the direction along (parallel) and perpendicular to the main axis of the carbon crystals.
The following carbon properties(graphite):
- coefficient of thermal linear expansion (KTlR), 1 / deg;
- specific (mass) heat capacity, J / (kg deg);
- thermal conductivity coefficient, W / (m · deg).
The table shows the values of the thermal conductivity of graphite of various densities at a temperature of 20 ° C. The thermal conductivity of graphite is indicated for the direction of the heat flow along the main axis of the crystals and in dimensions.
According to the table, it can be seen that thermal conductivity of graphite increases markedly with increasing density. The density of graphite in the table is given in dimensions 10 3 · kg / m 3, that is, in t / m 3. The density of graphite varies in the range from 1400 to 1750 kg / m 3.
The table shows the values of thermal conductivity of graphite with a density of 1650 ... 1720 kg / m 3 depending on temperature.
The thermal conductivity of graphite is indicated for the direction of the heat flow, both along and across the main axis of the crystals, the ratio of thermal conductivity in these directions is also indicated (it is constant and equal to approximately 1.5).
The values of the thermal conductivity of graphite are given in the temperature range from 20 to 1800 ° C. The values in the table show that thermal conductivity of graphite decreases with increasing temperature.
Thermal conductivity of reactor graphite with a density of 1700 kg / m 3 depending on temperature
The table shows the values of thermal conductivity of reactor graphite with a density of 1700 kg / m 3 depending on temperature.
Thermal conductivity is indicated in the direction of the heat flow, both parallel and perpendicular to the pressing of the graphite rods.
The thermal conductivity values of reactor graphite are given in the temperature range from 100 to 1700 K.
Thermal conductivity of crushed graphite
The table gives the thermal conductivity of crushed graphite (carbon) depending on the particle size at a temperature of 20 ° C.
Particle size was determined depending on the number of holes in the sieve per 1 square centimeter (3, 6, 16 holes / cm 2 and dry soot).
The thermal conductivity of graphite is indicated in units of W / (m · deg). The density of graphite in the table is indicated in 10 3 · kg / m 3, that is, in t / m 3.
Thermal conductivity of a layer of graphite particles depending on its porosity
The table shows the values of thermal conductivity of a layer of graphite particles (carbon particles) with a porosity of 0.4 to 0.7. It should be noted that with an increase in the porosity of the layer, its thermal conductivity decreases.
Coefficient of thermal expansion (CTE) of carbon (graphite) versus temperature
The table shows the values of the coefficient of linear thermal expansion (CTE) of carbon (graphite) depending on temperature.
CTE in the table is given for different grades of graphite: pyrolytic graphite, graphite based on petroleum coke, graphite based.
The coefficient of linear thermal expansion of graphite is given in the temperature range from 100 to 700 ° C in the dimension 1 / deg.
Heat capacity of carbon depending on temperature
The table shows the values of the heat capacity of carbon depending on temperature. The specific heat capacity of carbon (graphite) is indicated in the temperature range from 200 to 2000 K.
Heat capacity of carbon in the table the mass is given and is expressed in terms of kJ / (kg · deg). According to the data in the table, it can be seen that the heat capacity of carbon increases with temperature.
Heat capacity of natural carbon (graphite) at low temperatures
The table gives the values of the atomic (per 1 mol of substance) and specific heat capacity of carbon at low temperatures... The heat capacity of carbon (graphite) is indicated in the temperature range from -260 to 17 ° C.
Atomic heat capacity of carbon expressed in terms of J / (mol · deg). The specific heat capacity of carbon (mass - per 1 kg of mass) is expressed in terms of kJ / (kg · deg).
The values in the table clearly show that atomic and specific heat carbon (graphite) with increasing temperature grow at very low negative temperatures.
Sources:
1. Agroskin A.A., Gleybman V.B. Thermophysics solid fuel... M., Nedra, 1980 - 256 p.
2.
3. .
4. Industrial ovens. Reference manual for calculations and design. 2nd edition, supplemented and revised, Kazantsev E.I. M., "Metallurgy", 1975. - 368 p.
If you are interested in the question of what graphite is, you should know that it is a mineral, which is a representative of the class of native elements. It's a carbon modification. The structure is layered. Layer arrangement in crystal lattice different, this allows you to form polytypes.
Although graphite has been known for a long time, certain information about the history of its use cannot be obtained due to the similarities with other materials such as molybdenite. The material is electrically conductive. Compared to diamond, it has low hardness and softness. After exposure to impressive temperatures, it becomes harder, but becomes fragile.
Basic properties
What is graphite? If you also asked this question, then you should know about some of the physical properties. For example, the density can reach 2.23 g / cm³. As for the color, it is dark gray with a metallic sheen. The structure is infusible, it is resistant to heating in the absence of air.
The substance is slippery and greasy to the touch. Natural graphite contains 12% clay impurities and iron oxides. In the process of friction, flaking occurs, this property is used for the production of pencils. What is graphite, you cannot find out if you do not familiarize yourself with the basic characteristics of the type of thermal conductivity. It reaches 354.1 W / (m * K), and minimum value is equal to 100. The specific figure depends on the brand, temperature, and direction in relation to the reference planes.
Electrical conductivity is anisotropic. The coefficient of thermal expansion can be up to 700 K. The heat capacity varies from 300 to 3000K. Graphite ignites at 3500 ° C, turning into gaseous state, bypassing the liquid phase. But if at the same time as the temperature rises, the pressure increases to 1000 atmospheres, you can get molten material.
Crystal cell
The crystal lattice of graphite is composed of carbon atoms. It has a layered structure, and the step between the layers is 0.335 nm. The atoms are bonded to three other carbon atoms.
The grille can be of two types:
- hexagonal;
- rhombohedral.
In each layer, carbon atoms are opposite the centers of the hexagons in adjacent layers. Their position is repeated after one. Each is offset horizontally by 0.1418 nm
Chemical and mechanical properties
When wondering what graphite is, you should familiarize yourself with the basic properties. The material is chemically inert; it does not dissolve in substances other than molten metals. This applies to those who high melting... When diluted, carbides are formed, the most important of which are the following compounds:
- with boron;
- calcium;
- iron;
- titanium;
- tungsten.
At ordinary temperatures, it is rather difficult to combine graphite with other substances, but when exposed to impressive temperatures, chemical compound with many elements. Considering the properties of graphite, you will also highlight for yourself that the material does not have elasticity. But it can be cut and bent. The wire from it is easily twisted and bent into a spiral, and when rolling allows to achieve 10 percent elongation.
When testing a wire for tensile strength, this parameter is 2 kg / mm 2, while the bending modulus is equivalent to 836 kg / mm 2. Some of important properties are plasticity and fat content, which allowed the material to be widely used in industry. With an increase in fat content, the coefficient of friction decreases. The possibility of using it as a lubricant depends on this. Today, the ability of graphite to adhere to solid surfaces is also used.
Optical properties
Among the properties of graphite, one should also highlight optical. The light absorption coefficient remains constant over the entire spectrum. It is not affected by the radiation temperature of the body. If we consider thin graphite filaments, then the light absorption coefficient will be 0.77. This parameter decreases to 0.55 with an increase in graphite crystals.
When looking at pure material, you will notice that it has a negligible neutron absorption coefficient and the highest moderation coefficient. Thanks to this, it became possible to use it in nuclear reactors. Without graphite electrodes, the development of the non-ferrous and black chemical industries would have been impossible.
The field of application of graphite is also the lining of electrolyzers for aluminum production. Materials with a high carbon content are used for the construction of electric furnaces and other heating units. Graphite forms the basis of crucibles and boats for superhard alloys.
Main types
The formula of graphite is as follows: C. Its molar mass is 12 g / mol. The substance is simple. It is a mineral, non-metal, it is an allotropic modification of carbon. Among the main types should be highlighted:
- crucible;
- casting;
- rechargeable;
- elemental;
- for the production of rods;
- electric coal;
- for the manufacture of lubricants.
The first is used for refractory products, it is characterized by high thermal conductivity and resistance to temperature extremes. The use of casting crystalline graphite provides for the use of the material when casting parts. It has a low coefficient of expansion and is tough at high temperatures.
The battery variety is used as an additive and also in the manufacture of electrodes. Among the main characteristics are improved chemical and technical properties. In the production of rods, finely dispersed graphite is used, which does not contain iron impurities. For the manufacture of galvanic cells, an elemental variety is used, which is distinguished by high electrical and thermal conductivity. Graphite gray is also used to make electrically conductive rubber.
Artificial graphite
You know the formula of graphite, but this is not all you need to know if you are studying this substance. For example, today artificial graphite is produced, which can be fine-grained, structural, foundry, or antifriction. The area of use is wide enough.
The material is used in the manufacture of electrical installations and machines, refractory materials, in production and in the mining industry. Artificial graphite is used to make paints, as well as rechargeable batteries and coverings. Indispensable substance in narrowly focused areas like the nuclear industry.
Finally
V recent times interest in the described mineral has increased. On the basis of its fibers, materials such as carbon fiber, carbon fiber sorbents, composite materials based on carbon fiber, as well as carbon fiber materials are made. Special attention paid to carbon fiber, which is used in the chemical industry, as well as mechanical engineering.
The structure is layered. Well-formed crystals are rare; they look like hexagonal tablets with a well-developed basopinacoid face. Twins are noted. Usually forms scaly, columnar, massive, kidney-shaped, spherulite, spherulite-like and cylindrical zonal aggregates.
Dense-crystalline graphite composes veins and lenses in deposits of hydrothermal-pneumalite genesis or nests, and dissemination in contact-reaction deposits. Pneumatolite-associated with consonants, less often intersecting pegmatite, quartz, feldspar and calcite. Contact-reaction deposits are confined to the contact zones of carbon-rich carbonate and shale rocks with alkaline and gabbroid rocks, less often. composed of feldspar, quartz, less often micas, carbonate; in skarn zones, they are enriched in garnet, as well as in minerals and gabbroid rocks (nepheline, cancrinite, sodalite, sphene, apatite). Graphite (from coarse to fine crystalline) composes flaky and fibrous aggregates. The content in ores is 15-40%, in some deposits 60-90%. It is usually mined underground. The known deposits are Bogala (Sri Lanka) and Botogolskoe (CCCP).
Cryptocrystalline graphite has an imperfect texture and often contains an admixture of a finely dispersed carbonaceous substance. Forms powerful and extended bed-like deposits, sometimes turning into coals. The carbon content is 80-90%. The main rock-forming minerals are quartz, feldspar, sericite, chlorite, and calcite. Graphite is formed during the metamorphism of coals, coal and bituminous shales nearby. The deposits are developed by open-pit and underground methods. The main deposits are located in Mexico (Sonora state), South Kopee, Austria (Kaisersberg mine), CCCP (Noginskoe deposit).
Obtaining graphite
Along with natural, artificial graphite is used, which is obtained by cooling supersaturated alloys, thermal decomposition of gaseous hydrocarbons, heating, petroleum coke, coal tar pitch. Graphites are used in metallurgy (crucibles, casting molds, non-stick paints), in chemical engineering (lining material, pipes, etc.), in the production of collectors for dynamos, electrodes, conductive powders, lubricants, antifriction products, in nuclear technology, in the production of pencils, paints, thermal insulation materials. Artificial lumpy graphite is used as erosion-resistant coatings for rocket engine nozzles and nasal cone combustion chambers.
