Exfoliation of Graphite

When a graphite intercalation compound [1] is heated past a critical temperature, a large expansion along the c-direction occurs, giving the compound a puffed-up appearance. This phenomenom is known as exfoliation. Ubbelohde [2] observed that graphite-Br₂ exfoliated at 350°C from 3 mm to approximately 35 mm. Exfoliation has also been observed in graphite-FeC1₃ [3], graphite-A1C1₃ [4], and graphite intercalated with a mixture of HNO₃ and H₂SO₄ [4]. The exfoliation of graphite-FeC1₃ has been used to manufacture Grafoil [5]; the exfoliation of graphite-(HNO₃+H₂SO) has been used for making a thermal insulator for molten metals [6]. In spite of the numerous practical applications of exfoliation, relatively little work has been done to understand and characterize this unusual phenomenon.