The technological properties of graphite are mainly determined by its crystalline form. Graphite minerals with different crystalline forms have different industrial values and USES. In industry, natural graphite is divided into three types according to its crystalline form.
In a broad sense, all graphite materials obtained through organic carbonization and graphitization at high temperature can be called artificial graphite, such as carbon fiber, pyrolysis carbon, foamed graphite, etc. In a narrow sense, artificial graphite usually refers to bulk solid materials, such as graphite electrode and hydrostatic graphite, which are made by mixing, kneading, forming, carbonization and graphitization with low impurity carbonaceous materials as aggregate and coal tar as binder.
The forming methods of artificial graphite can be generally divided into: vibration molding, extrusion molding, molding, etc.
The massive graphite
Lumpy graphite is also called dense crystalline graphite. Such graphite crystals are clearly visible to the naked eye. The particle diameter is greater than 0. 1 mm, the specific surface area is concentrated in 0.1-1m2/g, and the crystals are arranged in a disorderly and dense block structure. This: graphite is characterized by high grade, generally with a carbon content of 60 ~ 65%, sometimes up to 80 ~ 98%, but its plasticity and slimy property are not as good as flake graphite.
2. Flake graphite
Graphite crystals are scaly; This is metamorphic under high pressure, with large scales and fine scales. This kind of graphite ore is characterized by low grade, generally between 2 ~ 3%, or 10 ~ 25%. It is one of the best flotation ores in nature. High grade graphite concentrate can be obtained by grinding and selecting. The floatability, lubricity and plasticity of this kind of graphite are superior to other types of graphite. So it has the highest industrial value.
3. Cryptocrystalline graphite
Cryptocrystalline graphite, also known as microcrystalline graphite or earthy graphite, generally has a crystal diameter of less than 1 micron and a specific surface area of 1-5m2/g. It is a combination of microcrystalline graphite and can only be seen in crystal form under electron microscope. This kind of graphite is characterized by a soil - like surface, lack of gloss, less lubricity than flake graphite. Good taste. The average is 60 to 85 percent. A few are over 90%. It is commonly used in casting industry. It is mainly located in lutang, chenzhou, hunan province. With the improvement of graphite purification technology. Earthy graphite is more and more widely used.
Special forming method
Edit graphite is used extensively in industry, almost every industry. Industrial use is artificial graphite, or special graphite. According to its forming way can be divided into the following kinds.
1.Isostatic graphite. That's what many people call triple high graphite, but it's not three high or equal static pressure.
2. Molded graphite
3. Extruded graphite, mostly electrode material.
According to the grain size of graphite, it can also be divided into: fine structured graphite, medium coarse graphite (the general grain size is around 0.8mm), and electrode graphite (2-4mm).
In a graphite crystal, the carbon atoms in the same layer form covalent bonds with sp2 hybridization, and each carbon atom is connected to the other three atoms with three covalent bonds. Six carbon atoms form a regular six-fold ring on the same plane, extending into a laminar structure. Here, the bond length of c-c bonds is 142pm, which is exactly within the range of the bond length of atomic crystals. Therefore, for the same layer, it is an atomic crystal. Carbon atoms in the same plane have one p orbital left, and they overlap. Electrons are free, which is the same thing as free electrons in metals, so graphite conducts heat and electricity, which is characteristic of metallic crystals. So it's also classified as a metallic crystal.
The middle layer and layer of graphite crystal are separated by 340pm, which is a large distance. It is bound by van der Waals force, that is, the layer and layer belong to molecular crystal. However, because the carbon atoms on the same plane layer are strongly bonded to each other and are extremely difficult to break down, the melting point of graphite is also high and its chemical properties are stable.
In view of its special bonding mode, it cannot be regarded as an atomic crystal or a molecular crystal alone. In modern terms, graphite is considered as a mixed crystal.
Crystal system and space group: hexagonal crystal system, P63/ MC
Crystal cell parameters: a0=0.246nm, c0=0.670nm
In a typical layered structure, carbon atoms are arranged in layers, and each carbon is equidistant from the adjacent carbon. The carbon in each layer is arranged in a six-sided ring. The distance between the upper and lower carbon atoms is much greater than that between the carbon in the same layer (the c-c spacing in the layer =0.142nm, and the c-c spacing between the layers =0.340nm).
Morphology: monocrystals are usually lamellar or plate-shaped, but integrity is rare. Aggregates are usually scaly, lumpy and earthy
Color: iron black
Stripe: bright black
Gloss: semi-metallic luster
Hardness: 1-2Cleavage and fracture: parallel cleavage is complete
Weight: 2.21 to 2.26 g/cm3
Specific surface area: 5-10m2/g
Other properties: thin film with flexibility, slippage, easy to stain hands, good electrical conductivity
Identification of characteristic iron black, low hardness, a set of complete cleavage, smooth feeling and dyeing hands; If the zinc particles moistened by the copper sulfate solution were placed on graphite, the spots of the metal copper could be precipitated, but not on the molybdenum deposits similar to graphite.