Expanded graphite 800

As a new functional carbon material, expanded graphite (EG) is a kind of loose and porous worm-like material obtained from natural graphite flakes through intercalation, washing, drying and high-temperature expansion. In addition to the excellent properties of natural graphite such as cold and heat resistance, corrosion resistance and self-lubrication, EG also has the characteristics of softness, compression resilience, adsorption, ecological and environmental coordination, biocompatibility and radiation resistance that natural graphite does not have. As early as the early 1860s, Brodie discovered expanded graphite by heating natural graphite with chemical reagents such as sulfuric acid and nitric acid. However, its application began after a hundred years. Since then, many countries have successively carried out the research and development of expanded graphite and made major scientific breakthroughs.
Expanded graphite can instantly expand 150~300 times in volume at high temperature, and change from flaky to vermicular, resulting in loose structure, porous and curved, expanded surface area, improved surface energy, enhanced adsorption of flake graphite, and self-chimerism between vermicular graphite, which increases its flexibility, resilience and plasticity.

Several development directions of expanded graphite are as follows:
1. Expanded graphite for special purposes
Experiments show that graphite worms have the function of absorbing electromagnetic waves, which makes expanded graphite have high military application value. Both the US military and our military have conducted experimental research in this area.
The expanded graphite must meet the following requirements:
(1) Low initial expansion temperature and large expansion volume;
(2) The chemical property is stable, and the expansion rate basically does not decay after 5 years of storage;
(3) The surface of expanded graphite is neutral and has no corrosion to the cartridge case.
2. Granular expanded graphite
Small-particle expanded graphite mainly refers to 300-purpose expandable graphite with an expansion volume of 100ml/g. This product is mainly used for flame-retardant coatings, and its demand is large.
3. Expanded graphite with high initial expansion temperature
The initial expansion temperature of expanded graphite with high initial expansion temperature is 290-300 ℃, and the expansion volume is ≥ 230ml/g. This kind of expanded graphite is mainly used for flame retardant of engineering plastics and rubber.
4. Surface modified graphite
When expanded graphite is used as a flame-retardant material, it involves the solubility of graphite and other components. Because of the high degree of mineralization on the surface of graphite, it is neither lipophilic nor hydrophilic. Therefore, it is necessary to modify the surface of graphite to solve the problem of compatibility between graphite and other components. Some people have proposed to whiten the surface of graphite, that is, to cover the surface of graphite with a solid white film. This is a difficult problem to solve. It involves membrane chemistry or surface chemistry, which may be achieved in the laboratory. There are difficulties in industrialization. This kind of white expandable graphite is mainly used as flame retardant coating.
5. Low initial expansion temperature and low temperature expanded graphite
This kind of expanded graphite starts to expand at 80-150 ℃, and its expansion volume reaches 250ml/g at 600 ℃. The difficulties in preparing expandable graphite meeting this condition are:
(1) Select appropriate intercalation agent;
(2) Control and master the drying conditions;
(3) Determination of moisture;
(4) The solution of environmental protection problems.
At present, the preparation of low-temperature expandable graphite is still in the experimental stage.

Performance
① Extremely strong pressure resistance, flexibility, plasticity and self-lubrication;
② Extremely strong resistance to high and low temperature, corrosion and radiation;
③ Extremely strong seismic characteristics;
④ Extremely strong conductivity;
⑤ Extremely strong anti-aging and anti twisting characteristics;
⑥ It can resist the melting and penetration of various metals;
⑦ It is non-toxic, free of any carcinogen, and has no harm to the environment;
The expansion characteristics of expandable graphite flakes are different from other expansion agents. When heated to a certain temperature, the expandable graphite starts to expand due to the decomposition of the compound absorbed in the interlayer lattice, which is called the initial expansion temperature. At 1000 ℃, the expandable graphite fully expands to the maximum volume. The expansion volume can reach more than 200 times of the initial value. The expanded graphite is called expanded graphite or graphite worm, which changes from the original flake shape to the worm shape with low density, forming a very good thermal insulation layer. Expanded graphite is not only the carbon source in the expansion system, but also the thermal insulation layer, which can effectively insulate the heat. It has the characteristics of low heat release rate, small mass loss and less smoke generated in the fire.
However, it can be seen from the existing literature that expanded graphite is an adsorbent with excellent performance, especially its porous structure and strong adsorption capacity for organic compounds. 1 g of expanded graphite can adsorb 80 g of oil, so expanded graphite is designed as an adsorbent for various industrial oils and oils.
Expanded graphite is very easy to absorb oil, organic molecules and hydrophobic substances. It has irreplaceable effects for water environmental protection treatment. When it is used for oil removal on water surface in granular form, its dosage is 1~lo%/rn, and the adsorption time can vary from 15 minutes to several hours according to the size of oil area on water surface and the type of oil.
Flexible graphite sealing materials are mainly divided into two categories according to their uses: one is used for sealing fillers on various pumps, valves and reactors; The other is graphite gasket used on various pipe flanges.
① Sealing packing
The sealing packing is a preformed packing which is directly formed on the press by winding the expanded graphite tape cut into appropriate width and length in the metal mold of different specifications. It is applicable to various stop valves, gate valves, regulating valves, ball valves, valves, etc.
② Sealing gasket
Generally, it can be divided into two types: one is pure graphite gasket, which is formed by directly pressing expanded graphite particles in the metal mold, or by directly punching or cutting expanded graphite plates; The other is graphite winding pad, which is made of metal tape and expanded graphite, and can be used under high pressure.
③ Graphite packing

Graphite packing is a sealing material woven with cotton fiber or graphite fiber and graphite foil. Graphite packing with cotton fiber core (SPM type) is suitable for sealing pipes, valves, pumps, etc. with pressure of 12MPa and temperature below 200 ℃. The contact medium can be river water, tap water, groundwater, sea water, oil, etc. Graphite packing with graphite fiber as the core (SPS type) is applicable to the sealing of pipes, valves, pumps, etc. with a pressure of 12MPa and a temperature below 350 ℃. In addition to all kinds of water and oil, the contact medium can also contact acid and alkali substances.
Compared with other adsorbents, expanded graphite has many advantages. If activated carbon is used to remove oil from water, it will sink after absorbing oil, and the adsorption amount is also small, and it is not easy to be recycled; There are also some adsorbents, such as cotton, straw ash, polypropylene fiber, perlite, vermiculite, etc., which absorb water while absorbing oil, which brings difficulties to post-treatment; Expanded graphite has a large adsorption capacity for oil. It floats on the water surface after oil absorption. It is easy to catch and recover. It is easy to recycle. It can be used by extrusion, centrifugal separation, vibration, solvent cleaning, combustion, heating extraction and other methods, and will not form secondary pollution.
Because expanded graphite not only retains the excellent properties of natural graphite such as high temperature resistance, corrosion resistance, radiation resistance and conductivity, but also has many unique excellent properties, such as flexibility, resilience, self-adhesiveness, impermeability, adsorption and low density, so it is particularly widely used in petroleum, chemical, atomic energy, electric power, pharmaceutical and other fields. With the progress of science and technology and the development of high technology, expanded graphite, a new engineering material, has gradually replaced some metal materials and organic synthetic materials in high-tech fields such as high speed, corrosion resistance, wear resistance and energy conservation.

Environmental protection
Expanded graphite is hydrophobic and lipophilic, and can selectively remove non-aqueous solutions in water, such as oil slick from sea, river and lake. Expanded graphite can form a certain winding space when absorbing oil, and can store oil substances that are much larger than its total pore volume. After absorbing a large amount of oil, it can be agglomerated and float on the liquid surface, which is convenient for collection, renewable treatment and recycling. Because expanded graphite is basically composed of pure carbon, non-toxic and chemically inert, it will not cause secondary pollution in water. In addition, expanded graphite can also be used to remove oil from industrial wastewater emulsion and oil-soluble substances, such as pesticides, and has good adsorption effect on many other organic or inorganic harmful components. In addition to selective adsorption in the liquid phase, expanded graphite also has a certain removal effect on the main components of air pollution such as SOx and NOx produced by industrial waste gas and automobile exhaust. [2]
Wang Luning and others used expanded graphite to treat printing and dyeing wastewater of wool textile factory. Under static conditions, the average removal rate of chemical oxygen demand (COD) in the wastewater reached 40%, and the average chroma decreased by 40%. During the field application, the average removal rate of COD in the wastewater reaches 20%, and the average chroma decreases by 20%. Field experiments show that expanded graphite has a unique application prospect in the treatment of wool textile printing and dyeing wastewater.
Liu Chengbao and others used expanded graphite as adsorbent to make a self-made adsorption column as a sewage treatment device. The results showed that when the water flow rate was controlled at 70L/h, the filling density was controlled at 9g/L, and the adsorption process was controlled at 2m, it could not only meet the reinjection standard of oilfield sewage, but also meet the economic requirements.
sealing material 
Expanded graphite can be post-processed into flexible graphite for use as a sealing material. Compared with traditional sealing materials (such as asbestos, rubber, cellulose and their composites), flexible graphite has a wide range of available temperatures, ranging from - 200 ℃ to 450 ℃ in the air, to 3000 ℃ in the vacuum or reducing atmosphere, and has a small coefficient of thermal expansion, which is not brittle and cracked at low temperature, and does not soften and creep at high temperature. Therefore, it is honored as the "king of sealing", and has been widely used in petrochemical, mechanical, metallurgical Atomic energy and other industries.
 

Biomedical science
Expanded graphite has good biocompatibility, non-toxic, tasteless, and no side effects, and is a very important biomedical material.
Shen Wanci et al. investigated the adsorption and absorption performance of expanded graphite as a medical dressing on simulated body fluid and the adsorption and inhibition performance of microorganisms (bacteria). The results showed that the adsorption and absorption capacity of expanded graphite on simulated body fluid was significantly higher than that of water and NaCl solution, and was significantly higher than that of ordinary absorbent gauze and non-stick gauze; The contact angle value to human plasma is close to 90 °, which indicates that expanded graphite is less sticky to the wound surface when used as dressing, which is beneficial to the replacement of dressing and reduces the pain of patients when changing dressing; It has adsorption effect on six kinds of bacteria in solid phase contact state, with bacteriostatic ring appearing, and has no pertinence on the type of bacteria, indicating that the bacteriostatic effect mainly comes from physical adsorption. Based on the excellent adsorption and drainage performance, air permeability and water permeability, small adhesion with the wound surface, the performance of non-staining black wound surface and the adsorption and inhibition performance of various bacteria, the expanded graphite composite material can be used as the external dressing of the wound surface with excellent performance, can replace the conventional gauze dressing, and has a good effect on burns and other wounds.
 

High energy battery material
Adding expanded graphite to the zinc anode of rechargeable zinc-manganese battery can reduce the polarization of the zinc anode during charging, enhance the conductivity of the electrode and electrolyte, inhibit the formation of dendrites, provide good molding characteristics, inhibit the dissolution and deformation of the anode, and extend the battery life. In addition, lithium can form GICs with graphite through gas, liquid, solid and lithium salt electrolysis. This GICs has low electrode potential and good intercalation reversibility.
Wu Juan studied the degradation effect of 4-chlorophenol in cotton cloth diaphragm electrolysis system with self-made expanded graphite modified activated carbon/polytetrafluoroethylene composite electrode as cathode, Ti/IrO2/RuO2 as anode, and Na2SO4 solution as electrolyte. The results show that when the addition of expanded graphite is 20% of the carbon material, and the ratio of PTFE to carbon material is 1:4, the electrode has the best degradation effect on 4-chlorophenol in the cathode chamber when the current density is 39 mA/cm, the electrolyte concentration is 0.05 mol/L, the initial concentration of 4-chlorophenol is 100 mg/L, the initial pH is 11, and the electrode spacing is 4 cm. The degradation rate of 4-chlorophenol in the cathode chamber is up to 98.7% when electrolysis is 120 mm.
 

Phase change heat storage material
The poor thermal conductivity and heat transfer performance of phase change heat storage materials affect their energy storage and release efficiency. At the same time, the porosity of the porous medium in the composite phase change material is small, and the content of the phase change material is small, resulting in its low energy storage. These shortcomings limit the application and development of the material. Expanded graphite has rich pore structure and high thermal conductivity, which can make up for these defects.
Zhang Zhengguo and others directly adsorbed paraffin on expanded graphite to prepare powdered paraffin/expanded graphite composite phase change heat storage materials, and carried out experimental research on the heat storage and exothermic properties of paraffin/expanded graphite composite phase change heat storage materials. The experimental results show that when the mass content of paraffin is 85.6%, the heat storage and heat release time of the composite phase change heat storage material is 27.4% and 56.4% shorter than that of paraffin, and the composite phase change heat storage material has good thermal stability of cycle performance.
Zhao Jianguo et al. prepared polyethylene glycol/expanded graphite phase change energy storage composites by using the adsorption properties of expanded graphite pore structure, and studied the thermal properties of the materials by differential scanning calorimetry. The results show that the phase change temperature of the composite does not change with the change of polyethylene glycol content, and the latent heat of phase change increases with the increase of polyethylene glycol content. The thermal conductivity of the composite decreases with the increase of polyethylene glycol content. The porous structure of expanded graphite has a good adsorption performance on polyethylene glycol. During the solid-liquid phase transition of polyethylene glycol, there is no liquid polyethylene glycol exudation.
 

Fire safety materials
Some expandable graphite has been added to the interlayer of the engine seat in foreign countries, or made into fire sealing strips, fire blocking materials, fire rings, etc. Once the fire expands rapidly, the fire spreading channel is blocked to achieve the purpose of fire extinguishing. In addition, the fine particles of expandable graphite can be added to the common coating to produce a flame retardant and antistatic coating with good effect.
Cai Xiaoxia et al. studied the synergistic flame retardancy of ammonium polyphosphate (APP) and expanded graphite (EG) ethylene-vinyl acetate copolymer (EVA) and its flame retardancy mechanism. The results showed that APP and EG had good synergistic flame retardancy on EVA.
 

Other
Expanded graphite sheet is a new type of heating material with good conductivity and thermal conductivity, electric heat conversion rate of more than 97%, and can produce far infrared ray. Expanded graphite is crushed into fine powder, which has strong scattering and absorption characteristics for infrared wave, and is a good infrared shielding (stealth) material. The expandable graphite is made into pyrotechnic powder, which explodes instantly to form expanded graphite and disperses in the predetermined airspace to form aerosol interference cloud smoke agent. In addition, expanded graphite can also be used as heat insulation, sound insulation materials, electromagnetic shielding elements, and catalytic materials.
Ren Hui et al. prepared expanded graphite doped with magnetic particles, and iron oxide was deposited on the surface of expanded graphite. With the increase of ferrocene input, the magnetic properties of expanded graphite increased more significantly, at 0 A/m-7.958 × The average magnetic intensity measured at 10A/m magnetic field intensity is ≥ 8emu/g, the maximum attenuation rate in the military millimeter wave radar frequency band is up to - 10dB, the mass extinction coefficient is greater than 1.0g/m, and the shielding effect is better than the active millimeter wave jamming agent. It is an efficient and reliable new radar shielding agent, and has broad application prospects in the field of electronic countermeasures.
Huang Mianfeng and others prepared the expanded graphite loaded TiO2 photocatalyst material. TiO2 is attached to the surface of the expanded graphite sheet in the form of nanoparticles. The expanded graphite has a special wormlike structure with loose pores, providing a three-dimensional degradation environment of high concentration for TiO2. The material is a floating photocatalyst, which is easy to be recycled and reused. After repeated use, the catalyst has no obvious deactivation and still shows high photocatalytic effect.