Expanding Graphite, as a new type of functional carbon material,(Expanded Graphite, abbreviated as EG) is a loose, porous, worm-like material obtained through intercalation, water washing, drying, and high-temperature expansion of natural graphite flake. EG not only possesses the excellent properties of natural graphite, such as heat and cold resistance, corrosion resistance, and self-lubrication, but also features characteristics not found in natural graphite, including softness, compressive resilience, adsorption, environmental compatibility, biocompatibility, and radiation resistance. As early as the early 1960s, Brodie discovered expanded graphite by heating natural graphite that had been reacted with chemicals like sulfuric acid and nitric acid. However, its applications only began a century later. Since then, many countries have successively carried out research and development on expanded graphite, achieving significant scientific and technological breakthroughs.
Expanding graphite can instantly increase in volume when exposed to high temperatures.150 to 300 times, changing from flake-like to worm-like, resulting in a loose, porous, and curved structure. This increases the surface area and surface energy, enhancing the adhesion force of flake graphite, allowing the worm-like graphite to interlock with each other, thereby increasing its flexibility, resilience, and plasticity.。
The expandable graphite sheets have a different expansion characteristic from other expandants. Upon reaching a certain temperature, due to the decomposition of compounds trapped in the interlayer lattice, the expandable graphite begins to expand, which is referred to as the initial expansion temperature, inAt 1000°C, it expands completely to its maximum volume, which can be over 200 times its original size. The expanded graphite, also known as graphite蠕虫, transitions from its original flake-like structure to a low-density worm-like form, creating an excellent insulating layer. Expanded graphite serves as both a carbon source in the expansion system and an insulating layer, effectively providing thermal insulation with low heat release rate, minimal weight loss, and reduced smoke generation during fires.
But it can be ascertained from existing literature that expanded graphite is an excellent adsorbent, particularly due to its loose and porous structure, which possesses strong adsorption capabilities for organic compounds.1 gram of expanded graphite can absorb 80 grams of oil, hence expanded graphite is designed as an adsorbent for various industrial greases and oils.
Expanding graphite readily absorbs oils, organic molecules, and hydrophobic substances, offering an irreplaceable effect in water environmental protection treatment. When used in granular form for oil removal on the water surface, the amount required depends on the size of the oil area and the type of oil.1~lo%/rn, adsorption time can vary from 15 minutes to several hours.
Flexible graphite sealing materials are mainly divided into two categories based on their applications: one type is used as sealing packing for various pumps, valves, and reactors; the other type is used as graphite gaskets on various pipeline flanges.
① Sealing Gasket
Sealed packing is a pre-formed packing material formed by wrapping expanded graphite strips cut to appropriate widths and lengths around metal molds of various specifications and then directly shaped on a press. It is suitable for various types of gate valves, globe valves, control valves, check valves, and additional valves.
② Sealing Gasket
Typically, they can be divided into two types: pure graphite gaskets, which are directly molded in metal molds from expanded graphite granules, or cut from expanded graphite sheets; and graphite wrapped gaskets, made by overlapping metal strips with expanded graphite, suitable for use under higher pressure.
③ Graphite Packing
Graphite packing is a sealing material woven from cotton fibers or graphite fibers along with graphite foil, with cotton fibers as the core.SPM Type is suitable for sealing applications on pipes, valves, pumps, etc., under pressures of 12MPa and temperatures below 200°C, with contact media including river water, tap water, groundwater, seawater, oils, and more. Graphite fiber core graphite packing (SPS Type) is suitable for sealing on pipes, valves, pumps, etc., under pressures of 12MPa and temperatures below 350°C, and can come into contact with various water, oils, as well as acidic and alkaline substances.
Compared to other absorbents, expanded graphite offers many advantages. For instance, when using activated carbon for oil removal on water, it sinks after absorbing oil, has a low adsorption capacity, and is not easily regenerated. Some other absorbents, such as cotton, ash, polypropylene fibers, perlite, and vermiculite, absorb both oil and water, which makes post-processing difficult. Expanded graphite has a high adsorption capacity for oils, floats on the surface after absorbing oil, is easy to harvest and recover, and can be easily regenerated. It can be processed using methods such as extrusion, centrifugal separation, vibration, solvent cleaning, combustion, and heat extraction, without causing secondary pollution.
Expanding Graphite not only retains the excellent properties of natural graphite, such as high-temperature resistance, corrosion resistance, radiation resistance, and electrical conductivity, but also possesses many unique qualities, including softness, resilience, self-adhesiveness, impermeability, adsorption, and low density. Consequently, its applications are particularly extensive in the oil, chemical, nuclear energy, and power industries. With the advancement of technology and the development of high-tech, this new engineering material, expanding graphite, is gradually replacing certain metals and organic synthetic materials in high-tech fields such as high-speed operation, corrosion resistance, wear resistance, and energy saving.
