Exfoliated Graphite Formed by Intercalation

When a graphite intercalation compound (GIC) is heated, a thermal expansion, large (~3.5 × 10−5/K) compared with most materials, occurs along the c-axis, while the in-plane lattice constant remains almost unchanged. This anisotropic thermal expansion behavior is reversible and can be modeled in terms of a superposition of the c-axis thermal expansion coefficients of the constituent layers (Salamanca-Riba and Dresselhaus, 1986). However, when a GIC is heated above a specific critical temperature, a gigantic c-axis expansion can occur, with sample elongations (ΔLS/LS) of a factor of 300 (Inagaki et al., 1983). This extremely large elongation, also called “exfoliation,” is generally irreversible, and leads to a spongy, foamy, low-density, high-surface-area carbon material of about 85 m2/g (Thomy and Duval, 1969). This exfoliation effect alters the structural integrity of the GIC material and therefore is undesirable for structural applications of GICs. However, this spongy, foam-like material is advantageous for some applications, such as gas adsorption. The commercial version of the exfoliated wormy-like material is called vermicular graphite from its appearance, and is used for high-surface-area applications. Furthermore, when pressed into sheets, it is called grafoil and is widely used as a high-temperature gasket or packing material because of its flexibility, chemical inertness, low transverse thermal conductivity, and ability to withstand high temperatures. Grafoil-type products can also be used to contain molten corrosive liquid metals at high temperatures and to extinguish metal fires (Anderson and Chung, 1984). These products have been expected to be useful for oil adsorption (Toyoda et al., 1998a, 1998b, 1999). In this chapter, the preparation and conventional as well as advanced applications of exfoliated graphite with unique properties, obtained from QIC-based materials, is demonstrated.