Expandable graphite
Characteristics
If heated, the graphite flakes will expand to a multiple of its volume. If expandable graphite is heated, the graphite flakes will expand to a multiple of its volume. The main products in the market have a starting temperature in the range of 200 °C. The expanded flakes have a “worm-like” appearance and are generally several millimeters long.[1]
| Physical characteristics | |
|---|---|
| Carbon content | 85%-99% |
| Expansion rate | 30–400 cm³/g |
| Particle size | 80 % < 75 µm – 80% > 500 µm |
| Starting temperature | 140 °C-230 °C |
Production
To produce expandable graphite, natural graphite flakes are treated in a bath of acid and oxidizing agent.Usually used oxidizing agents are hydrogen peroxide, potassium permanganate or chromic acid. Concentrated sulphuric acid or nitric acid are usually used as the compound to be incorporated, with the reaction taking place at temperatures of 30 °C to 130 °C for up to four hours. After the reaction time, the flakes are washed with water and then dried.[2] Starting temperature and expansion rate depend on the production conditions and particle size of the graphite. temperature and expansion rate are depending on the degree of fineness of the graphite used.
Applications
Flame retardant
One of the main applications of expandable graphite is as a flame retardant. When exposed to heat, expandable graphite expands and forms an intumescent layer on the material surface. This slows down the spread of fire and counteracts the most dangerous consequences of fire for humans, the formation of toxic gases and smoke. [3]
Graphite foil
By compressing expanded graphite, foils can be produced from pure graphite. These are mainly used as thermally and chemically highly resistant seals in chemical plant construction or as heat spreaders.
Expandable graphite for metallurgy
Expandable graphite is also used in metallurgy to cover melts and moulds. The material serves here as an oxidation protection and insulator.
Expandable graphite for the chemical industry
Expandable graphite is included in the chemical processes for paints and varnishes.
References
- ^ Cite error: The named reference
:0was invoked but never defined (see the help page). - ^ Europäische Patentschrift EP 1 323 670 B1 from 8. Juli 2009
- ^ Mineralischer Flammschutz mit Blähgraphit – Der hochwirksame und REACH-konforme Intumeszenzbildner Pressemitteilung Georg H. Luh GmbH.