Multi-field applications of expandable graphite

Graphite crystal has a hexagonal network plane layered structure composed of carbon elements. The carbon atoms on the layer plane are combined with strong covalent bonds, while the layers are combined with van der Waals force, the bond is very weak, and the distance between the layers is large. , Therefore, under appropriate conditions, various chemical substances such as acids, alkali metals, salts, etc. can be inserted between the graphite layers and combined with carbon atoms to form a new chemical phase-graphite intercalation compound (GIC for short). When this interlayer compound is heated to an appropriate temperature, it can be rapidly decomposed in an instant, producing a large amount of gas, which expands the graphite into a worm-like new substance along the axis, namely expanded graphite. This unexpanded graphite interlayer compound is expandable graphite. Expandable graphite can be used in many materials, as follows:

1. Sealing material

The raw material high-carbon graphite is mixed with concentrated sulfuric acid and concentrated nitric acid for acidification treatment, heat treatment, and then compression molding. The prepared flexible graphite is a new type of high-performance sealing material and an in-situ growth nanomaterial. Compared with traditional sealing materials such as asbestos rubber, it has excellent properties such as good compressibility, resilience, self-adhesion, and low density, and can be used for a long time under harsh conditions such as high temperature and high corrosion. The graphite sheets and sealing components made of it are widely used in aerospace, machinery, electronics, nuclear energy, petrochemical, electric power, shipbuilding, smelting, and other industries. Because it has excellent characteristics such as lightweight, electrical conductivity, thermal conductivity, high-temperature resistance, acid, and alkali corrosion resistance, good resilience, lubricity, plasticity, and chemical stability, it is known as the “king of seals” in the world.

2. Environmental protection

The expandable graphite obtained by high-temperature expansion has a rich pore structure, so it has excellent adsorption performance, so it has a wide range of uses in environmental protection and biomedicine. The pore structure of expandable graphite has two kinds of open pores and closed pores, and the pore volume accounts for about 98%. Because it is dominated by macropores and mesopores, it is also different in adsorption characteristics from microporous materials such as activated carbon. It is suitable for liquid-phase adsorption but not for gas-phase adsorption. It is lipophilic and hydrophobic in liquid phase adsorption. 1g of expandable graphite can absorb more than 80g of heavy oil, so it is a promising environmentally friendly material for removing oil pollution from water surfaces. In the wastewater treatment of chemical enterprises, microorganisms (bacteria) are often used for treatment. Expandable graphite is a good microbial carrier, especially in the treatment of water contaminated by oily organic macromolecules. Regeneration and reuse, so it has a good application prospect.1. Sealing material2. Environmental protection.

3. Medicine

Expandable graphite has a wide range of application prospects in biomedical materials due to its adsorption properties to organic and biological macromolecules.

4. High-energy battery materials

As a battery material, expandable graphite uses the free energy change of the interlayer reaction of expandable graphite to convert it into electrical energy. Usually, expandable graphite is used as the cathode, lithium is used as the anode, expandable graphite composite silver oxide is used as the cathode, and zinc is used as the anode. Expandable graphites of fluorinated graphite, graphitic acid, and metal halides such as AuCl3 and TiF4 have been used in batteries.

5. Flame retardant and fireproof, fireproof sealing strip

Due to the expandability of expandable graphite and its high-temperature resistance, expandable graphite has become an excellent sealing material and is widely used in fireproof sealing strips. There are two main forms: the first is to mix, vulcanize, and shape expandable graphite materials with rubber materials, inorganic flame retardants, accelerators, vulcanizing agents, reinforcing agents, fillers, etc. to make various specifications of expansion. Sealing strip, mainly used in fire doors, fire glass windows, and other occasions. This inflatable sealing strip can block the flow of smoke from beginning to end in normal temperature and fire. The other is to use glass fiber tape as a carrier, and bond the expandable graphite to the carrier with a certain adhesive. The shear resistance provided by the carbide formed by the adhesive at a high temperature can effectively prevent the graphite slide. It is mainly used for fire doors, but it cannot effectively block the flow of cold smoke at normal or low temperatures, so it must be used in conjunction with normal temperature sealants.

6. Flame retardant of plastic materials

Expandable graphite is a good flame retardant for plastic materials. It has the characteristics of non-toxicity and non-polluting. It can achieve an ideal flame retardant effect when used alone or mixed with other flame retardants. When expandable graphite achieves the same flame retardant effect, the dosage is much smaller than that of ordinary flame retardants. Its principle of action is: at high temperature, the expandable graphite expands rapidly, suffocating the flame, and at the same time, the generated graphite expanded material covers the surface of the substrate, which isolates the contact between heat radiation and oxygen; the acid radicals inside the interlayer expand when they expand. The release also promotes the carbonization of the substrate, to achieve good results through a variety of flame retardant methods.

7. Fireproof bag, plastic fireproof blocking material, fireproof ring

Because expandable graphite can resist damage at high temperatures and has a high expansion rate, it can be used as an effective intumescent flame retardant material in fireproof bags, plastic fireproof plugging materials, and fireproof rings components, and is used for fireproof sealing in buildings. Blocking (for example: sealing building pipes, cables, wires, gas, gas pipes, holes through which air pipes pass, etc.).

8. Application of paint

When fine particles of expandable graphite are added to ordinary coatings, a flame retardant and antistatic coating with better effect can be obtained, and its high-temperature resistance and fire resistance can be improved. A large number of lightweight non-combustible carbon layers formed in the fire can effectively block the radiation of heat to the substrate and effectively protect the substrate. In addition, because graphite is a good electrical conductor, the prepared coating can prevent the accumulation of electrostatic charges and can be used in petroleum storage tanks to achieve the dual effect of fire prevention and anti-static.

9. Fireproof board, fireproof paper, anti-corrosion, and high-temperature board

The metal base layer is lined with an expandable graphite layer, a carbonized bonding layer is arranged between the expandable graphite layer and the metal base layer, and the expandable graphite layer is covered with a carbonized protective layer. With anti-corrosion, high temperature, and high-pressure performance. At the same time, it is resistant to thermal shock and can be used normally at low temperatures. It is not afraid of rapid cooling and rapid heating and has excellent thermal conductivity. The operating temperature is – 100 ~ 2000 ℃. Wide application range, easy manufacture, and low cost. In addition, graphite paper made by expanding expandable graphite at high temperatures is also used in places where fire and heat preservation are required.