Expanded Graphite The graphite graphite is a two-way macromolecule lamellar structure, and the C atoms in each plane are combined with C-C covalent bonds, and the layers are combined with the weak van der Waals forces. The layered structure of graphite is very typical, each layer is a carbon atom layer, between layers of carbon atoms to sp2 hybrid orbit into a strong covalent bond, that is, a 2s electrons and two 2p electronic hybrid The hybrid orbital of the price is located on the same plane, forming a σ bond with each other, and two 2P electrons that do not participate in the hybrid are perpendicular to the plane to form a bond. This layered structure of graphite makes the layers there is a certain gap. Therefore, under certain conditions, some reactants (such as acid, alkali, halogen) atoms (or a single molecule) can enter the inter-layer gap, and carbon network plane to form interlayer compounds. This kind of intercalation of graphite is expansive graphite. The carbon atoms are interconnected by a weak van der Waals force, which allows the intercalation material to smoothly enter the carbonaceous layer without destroying the hexagonal network in the carbon atom layer, so that the natural graphite is a graphite intercalation compound The best maternal material. Expandable graphite is a physical or chemical method to make non-carbon reactants into the graphite layer, with the carbon hexagonal network plane while maintaining the graphite layer structure of the crystal compounds. It not only retains the excellent physical and chemical properties of graphite, but also because of the interaction between the insert material and the graphite layer presents the original graphite and intercalation material does not have the new performance. In the presence of high temperature, the interlayer compound will decompose to produce a thrust along the C-axis direction of the graphite interlayer, which is much larger than the interlayer adhesion of the graphite particles. Under the action of this thrust The graphite layer is pushed open, so that the graphite particles in the C-axis direction of high expansion, the formation of worm-like expansion of graphite l2]. Between the graphite layer and the layer can be "embedded" into the chemical and has a swellable. Such as sulfuric acid can be used to deal with graphite, graphite graphite after drying at high temperatures, which is due to sulfuric acid molecules "embedded" into the graphite layer.
Expanded graphite several development direction is as follows:
1, special purpose expansion of graphite
Experiments show that graphite worms have the function of absorbing electromagnetic waves, which makes the expanded graphite have high military application value. The US military and our military have conducted this experimental study. This expansion of graphite must meet the following requirements: (1) the initial expansion temperature is low, the expansion of large volume; (2) chemical stability, storage 5 years, the expansion rate is basically not attenuated; (3) expanded graphite surface was neutral, Cartridge shell without corrosion.
2, particles expanded graphite
Small particles of expanded graphite mainly refers to 300 mesh expandable graphite, the expansion volume of 100ml / g, the product is mainly used for flame retardant coating, the demand is very large.
3, high initial expansion temperature of the expanded graphite
The initial expansion temperature of the expanded carbon at a high initial expansion temperature is 290-300 ° C and the expansion volume is ≥ 230 ml / g. This type of expanded graphite is mainly used for engineering plastics and rubber flame retardant, the product has been successfully developed by Hebei Agricultural University and applied for a national patent.
4, surface modified graphite
Expanded Graphite Expanded graphite as a flame retardant material, involving the compatibility of graphite and other components of the problem, because the graphite surface of the high degree of salinity, it is neither lipophilic substances, not hydrophilic substances. So the graphite surface must be modified to solve the graphite and other components of the compatibility problem. It has been proposed to whiten the surface of the graphite, that is, on the surface of graphite covered with a layer of solid white film, which is a difficult problem to solve, involving membrane chemistry or surface chemistry problems, the laboratory may do, industrial problems. This type of white expandable graphite is mainly used for flame retardant coating
5, Expanded Graphite low initial expansion temperature, low temperature expansion graphite
Such expanded graphite began to expand the temperature of 80-150 ℃, 600 ℃ expansion volume of 250ml / g. (2) the control and mastery of drying conditions; (3) the determination of moisture; (4) the solution of environmental problems. At present, the preparation of low temperature expandable graphite is still in the experimental stage