Carbon in Modern Industries---Expanded graphite

Carbon is the source of life, the skeleton element of all living organisms on earth, and the most important element that constitutes the human body. Carbon in Modern Industries is mainly used as precision heaters, high-strength structures, new batteries, nuclear reactors, etc. in the form of expanded graphite, isostatic graphite, and pyrolytic graphite.

Expanded Graphite (EG), as a new type of functional carbon material, is a loose and porous worm-like substance 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 softness, compression resilience, adsorption, ecological environment coordination, biocompatibility, radiation resistance and other characteristics that natural graphite does not have.

Application areas:

1. In the field of environmental protection, expanded graphite is hydrophobic and lipophilic, and can selectively remove non-aqueous solutions in water, such as removing oil slicks from the sea, rivers, and lakes.

2. In biomedicine, expanded graphite has the characteristics of good biocompatibility, non-toxicity, tasteless and no side effects, and is a very important biomedical material.

3. High-energy battery material, adding expanded graphite to the zinc anode of a 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, and provide good molding properties， can inhibit anode dissolution and deformation, prolong battery life.

4. Phase change heat storage materials, phase change heat storage materials have poor thermal conductivity and poor heat exchange performance, which affect their energy storage and energy release efficiency. At the same time, the porosity of the porous medium in the composite phase change material is small, and the phase change material contained in it is small, resulting in low energy storage. These shortcomings limit the application and development of the material. The rich pore structure and high thermal conductivity of expanded graphite can make up for these defects.

5. Fire safety materials, foreign countries have added some expandable graphite to the interlayer of the cabin seat, or made it into fire seals, fire blocking materials, fire rings, etc. Once a fire starts, it expands rapidly and blocks the fire spread channel to achieve fire fighting purpose. In addition, adding the fine particles of expandable graphite into ordinary coatings can produce better flame retardant and antistatic coatings.

Chinese scientists have studied the synergistic flame retardant ethylene-vinyl acetate copolymer (EVA) and its flame retardant mechanism of ammonium polyphosphate (APP) and expanded graphite (EG). The results show that APP and EG have a good synergistic flame retardant effect on EVA.

6. Sealing material, expanded graphite can be post-processed into flexible graphite for use as sealing material.

Flexible graphite sealing materials are mainly divided into two categories according to their uses: one is used for sealing packing on various pumps, valves and reaction kettles; the other is graphite gaskets used on various pipeline flanges.

6.1 Seal packing. Sealing packing is a preformed packing that is directly formed on a press by winding expanded graphite ribbons cut into appropriate widths and lengths in metal molds of different specifications. Applicable to various globe valves, gate valves, regulating valves, ball valves, adding valves, etc.

6.2 Sealing gaskets can usually be divided into two types, one is pure graphite gaskets, which are directly pressed into metal molds with expanded graphite granules, or directly punched or cut from expanded graphite sheets; the other one is graphite wound pad, which is made of metal tape and expanded graphite overlapped and rolled, and can be used under higher pressure.

6.3 Graphite packing, graphite packing is a sealing material woven graphite coil foil with cotton fiber or graphite fiber. The graphite packing with cotton fiber as the core (SPM type) is suitable for the sealing of pipes, valves, pumps, etc. with a pressure of 12MPa and a temperature below 200℃. The contact medium can be river water, tap water, groundwater, seawater, oil, etc. The graphite packing with graphite fiber as the core (SPS type) is suitable for the sealing of pipes, valves, pumps, etc. with a pressure of 12MPa and a temperature below 350℃. The contact medium can be acid and alkali substances in addition to various water and oil.