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Graphite intercalation compound
In the area of solid state chemistry, graphite intercalation compounds are a family of materials prepared from graphite. In particular, the sheets of carbon that comprise graphite can be pried apart by the insertion (intercalation) of ions. The graphite is viewed as a host and the inserted ions as guests. The materials have the formula (guest)Cn where n ≥ 6. The insertion of the guests increases the distance between the carbon sheets. Common guests are reducing agents such as alkali metals. Strong oxidants also intercalate into graphite. Intercalation involves electron transfer into or out of the carbon sheets. So, in some sense, graphite intercalation compounds are salts. Intercalation is often reversible: the inserted ions can be removed and the sheets of carbon collapse to a graphite-like structure.
The properties of graphite intercalation compounds differ from those of the parent graphite.
These materials are prepared by treating graphite with a strong oxidant or a strong reducing agent:
The reaction is reversible.
The host (graphite) and the guest X interact by charge transfer. An analogous process is the basis of commercial lithium-ion batteries.
In a graphite intercalation compound not every layer is necessarily occupied by guests. In so-called stage 1 compounds, graphite layers and intercalated layers alternate and in stage 2 compounds, two graphite layers with no guest material in between alternate with an intercalated layer. The actual composition may vary and therefore these compounds are an example of non-stoichiometric compounds. It is customary to specify the composition together with the stage. The layers are pushed apart upon incorporation of the guest ions.
One of the best studied graphite intercalation compounds, KC8, is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite. KC8 is a superconductor with a very low critical temperature Tc = 0.14 K. Heating KC8 leads to the formation of a series of decomposition products as the K atoms are eliminated:[citation needed]
Via the intermediates KC24 (blue in color), KC36, KC48, ultimately the compound KC60 results.
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Graphite intercalation compound
In the area of solid state chemistry, graphite intercalation compounds are a family of materials prepared from graphite. In particular, the sheets of carbon that comprise graphite can be pried apart by the insertion (intercalation) of ions. The graphite is viewed as a host and the inserted ions as guests. The materials have the formula (guest)Cn where n ≥ 6. The insertion of the guests increases the distance between the carbon sheets. Common guests are reducing agents such as alkali metals. Strong oxidants also intercalate into graphite. Intercalation involves electron transfer into or out of the carbon sheets. So, in some sense, graphite intercalation compounds are salts. Intercalation is often reversible: the inserted ions can be removed and the sheets of carbon collapse to a graphite-like structure.
The properties of graphite intercalation compounds differ from those of the parent graphite.
These materials are prepared by treating graphite with a strong oxidant or a strong reducing agent:
The reaction is reversible.
The host (graphite) and the guest X interact by charge transfer. An analogous process is the basis of commercial lithium-ion batteries.
In a graphite intercalation compound not every layer is necessarily occupied by guests. In so-called stage 1 compounds, graphite layers and intercalated layers alternate and in stage 2 compounds, two graphite layers with no guest material in between alternate with an intercalated layer. The actual composition may vary and therefore these compounds are an example of non-stoichiometric compounds. It is customary to specify the composition together with the stage. The layers are pushed apart upon incorporation of the guest ions.
One of the best studied graphite intercalation compounds, KC8, is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite. KC8 is a superconductor with a very low critical temperature Tc = 0.14 K. Heating KC8 leads to the formation of a series of decomposition products as the K atoms are eliminated:[citation needed]
Via the intermediates KC24 (blue in color), KC36, KC48, ultimately the compound KC60 results.