China is a large country with natural graphite resources (2/3 of the world's reserves are in China). Graphite is an inorganic substance, chemical composition is C, belongs to hexagon crystal system, the crystal is in the shape of hexagon plate and flake, the aggregate is in the shape of scale, iron black, the density is 2.25g/cm3, has sliding feeling, can conduct electricity, the chemical property is not lively, has the corrosion resistance. Expandable graphite is a product of natural flake graphite which is chemically or electrochemically treated. From natural flake graphite of expandable graphite materials both retained the graphite of high temperature resistant, corrosion resistant, can withstand the neutron flux, beta, gamma irradiation for a long time, low friction coefficient, good self-lubrication, thermally conductive and anisotropic properties, and have no natural graphite bendable, compressible, elastic, permeability etc., and porous. Under high temperature, high pressure or radiation conditions, no decomposition, deformation or aging occurs, and the chemical properties are stable.
Graphite with layered structure, alkali metal, halogen metal halide, strong oxidizing oxyacid etc. Can be embedded into the interlayer, cambium between compounds, in high temperature is above 200 ℃, due to stay in the compound layer lattice absorption decomposition, graphite layer compound decomposition, gasification, sharply between inflation (150-250 times the interlayer expansion), make the expandable graphite began to swell, and at the age of 1100 ℃ maximum volume. The final volume can reach 280 times of the initial volume, thus producing worm-like graphite with extremely low density (0.003-0.005g/cm3), which is a loose, soft and ductile substance, so it is usually called flexible graphite.
2. Friendly properties of expandable graphite
In theory, can withstand the expansible graphite - 200-3650 ℃ temperature change (non oxidizing medium), but the specific surface area of the expandable graphite are much larger than that of natural graphite, so in fact the expansible graphite oxidation temperature is lower than natural graphite, actually use temperature to - 204-204 ℃, its expansion temperature about 300 ℃. On the current domestic industrial application of the temperature reached 850 ℃, the pressure is 2.8 MPa, the temperature is 1500 ℃ of pure oxygen combustion, explosion in medium, also have no obvious chemical changes.
3. Application of expandable graphite in fireproof coatings classification of fire-resistant coatings
Fire retardant coatings can be divided into non-expansive fire retardant coatings and expansive fire retardant coatings according to their different fire prevention mechanisms. Non-expansive fireproofing coatings are made of refractory resin, flame retardant, fireproofing filler, etc. It can also be made of inorganic salts into adhesive, with mica, boron and other inorganic salts such as processing. This kind of coating relies on its own incombustible or non-combustible to achieve the purpose of fire retardant, the protective layer that forms when burning is thinner, heat insulation is poor, can only resist instantaneous high temperature and flame, and the coating is thicker. Intumescent fire coatings on polymer base makings, add the foaming agent, dehydration catalyst, carbonation agent carbon fire protection components, such as coating formed in the expandable flame and high temperature carbonization is compact and uniform of the honeycomb or spongy carbon foam layer, the thickness of the foam layer thickness is the original film dozens of times on even one hundred times, can well isolated from oxygen and heat conduction; And the coating before expanding is thinner commonly, be helpful to satisfy adornment requirement.