Editing Graphite (section)

===Expanded graphite===
Expanded graphite is made by immersing natural flake graphite in a bath of [[chromic acid]], then concentrated [[sulfuric acid]], which forces the crystal lattice planes apart, thus expanding the graphite. The expanded graphite can be used to make graphite foil or used directly as a "hot top" compound to insulate molten metal in a ladle or red-hot steel ingots and decrease heat loss, or as [[firestop]]s fitted around a [[fire door]] or in sheet metal collars surrounding plastic pipe (during a fire, the graphite expands and chars to resist fire penetration and spread), or to make high-performance gasket material for high-temperature use. After being made into graphite foil, the foil is machined and assembled into the bipolar plates in [[fuel cells]].
The foil is made into heat sinks for [[laptop computers]] which keeps them cool while saving weight, and is made into a foil laminate that can be used in valve packings or made into gaskets. Old-style packings are now a minor member of this grouping: fine flake graphite in oils or greases for uses requiring heat resistance. A GAN estimate of current US natural graphite consumption in this end-use is 7,500&nbsp;tonnes.<ref name=usgs/>