Graphite is a mineral, a stable crystalline modification of carbon. It retains its original properties under standard conditions. The material is refractory, sufficiently dense and has high electrical conductivity. It turns out by heating anthracite without air access. It is used in foundries, in the manufacture of steel, as well as for lubrication in rolling production. But these areas do not cover all areas of use.
Basic Features
If you are interested in the question of what is the density of graphite, you should know that this parameter is 2230 kg/m3. Another allotropic form of carbon is diamond, which is why graphite is sometimes compared to it. The latter has electrically conductive characteristics and acts as a semimetal. This property has found its way into the electrode manufacturing process.
The density of graphite is not all you need to know if you are interested in this mineral. There are other properties to consider as well. For example, this crystalline modification of carbon does not melt, but whenexposed to a temperature of 3500 °C ignites. The material passes the liquid phase, passing into the gaseous state.
However, if the conditions provide for an increase in pressure up to 90 MPa, as well as temperature, then melting can be achieved. This discovery was made while studying the properties of diamond when they were trying to synthesize it. But it was not possible to obtain this material from molten graphite.
Crystal lattice
The crystal lattice of graphite provides for the presence of carbon atoms. It has a layered structure. The distance between individual layers can reach 0.335 nm. In the lattice, carbon atoms bond with three other carbon atoms.
The lattice can be hexagonal and rhombohedral. In each layer, carbon atoms are located opposite the central parts of the hexagons. The latter are in adjacent layers, then the position of the layers is repeated, which happens after one.
Production of artificial graphite
Graphite and its properties is not the only thing you should know if you are interested in this mineral. It is also important to ask about the production of an artificial variety. It differs from a natural material in that the synthesis produces a substance with specified parameters.
Waste of petroleum coke and coal sand are used in production. A mixture of fine-grained elements is fired, and then cooled for about 5 weeks. The impact of temperature at the first stage is accompanied by itsup to 1200 °C.
To increase the theoretical density of graphite, workpieces are impregnated with sand. At the final stage, graphitization takes place, it involves heat treatment of the material in a special furnace, where the temperature reaches 3000 °C. In this case, it is possible to form a crystal lattice.
This graphite has high thermal conductivity and excellent electrical conductivity. The anisotropy of properties is inherent in a mineral obtained by extrusion. Today, a newer technology is used, which is called isostatic pressing. This makes it possible to produce a material that has a low coefficient of friction. It has isotropic properties.
The density of graphite (g/cm3), which is obtained during the extrusion process, reaches 2.23. The same indicator for the isostatic recrystallized variety, depending on the brand, can reach 5 g/cm3. Such material is used for the manufacture of large-sized blanks, the length and diameter of which are 1000 and 500 mm, respectively, as well as for the production of casting parts and molds that have anti-friction properties.
Main Brands
Today, the possibility of synthesis with different grain sizes is used. As a result, graphite can be classified into:
- coarse;
- medium;
- fine-grained;
- fine-grained.
Elements of the first reach a diameter of 3,000 microns. If we are talking about a medium-grained variety, then the grain size is 500µm. Fine-grained graphite grade MPG with a grain size of up to 50 microns is distinguished. There is also a fine-grained isotropic mineral of the MIG-1 brand, the particles of which have sizes from 30 to 150 microns. Fine-grained graphite and isostatic graphite have grains up to 30 microns in size, their minimum diameter is 1 micron.
Using artificial graphite
You already know the density of graphite. However, it is also important to study the area of use of the artificial variety. It is applied in all industries. Electrodes are made from coarse-grained. Fine-grained structural goes to the production of shaped products that have a complex shape.
The use of an artificial mineral made it possible to achieve high precision in the manufacture of parts. Today, equipment is produced that fully meets the standards of this century.
Additional information on density and thermal expansion
Depending on the additive, the highest density of graphite can be 5g/cm3. The minimum value is 2. It is inherent in recrystallized graphite. Single crystals have a high anisotropy, this is due to the structure of the crystal lattice. In the basal planes, thermal expansion is negative up to 427 °C. This suggests that the mineral is shrinking.
With increasing temperature, its absolute value decreases. At the above temperature level, thermal expansion is positive. Itdirected perpendicular to the basal planes. The temperature coefficient of expansion is almost independent of temperature and exceeds the value by more than 20 times compared to the average absolute coefficient for the basal planes.
What else you need to know about durability
The strength and density of graphite change with increasing temperature. For most artificial graphites, the tensile strength increases by a factor of 2.5 with increasing temperature. The maximum value reaches at 2800 °C.
The compressive strength increases by 1.6 times when the temperature reaches 2,200 °C. The shear and elasticity moduli increase by 1.6 times when the temperature reaches 1,600 °C.
In closing
Shape determines the types of graphite, which can be: lamellar, flaky and spherical. Flake is also called carbon annealing. Graphite is also a microstructural constituent of malleable, gray ductile iron and compacted graphite cast iron. In this case, it is composed of carbon and determines the specific properties of cast iron.
This material was used to create inscriptions and drawings about 4,000 years ago. Its name comes from the word "write". The deposits are located where deposits of bitumen and hard coal have been exposed to high temperatures.
