300 K

Diamond and graphite have extended network structures, whereas C60 crystals are molecular solids in which the molecules are bound together by Van der Waals forces. This is reflected in the low melting temperature of C60 compared with diamond and graphite. The high volumetric density of strong sp3 bonds in diamond leads to a very high value of Young's modulus. For similar reasons, the value of Young's modulus for graphite in the basal plane is comparable to that of diamond. This is exploited in the development of high modulus carbon fibers that have basal planes preferentially oriented along the fiber axis, see Chapters 4 and 5. However the weak Van der Waals bonding between basal planes in graphite results in a low value of Young's modulus perpendicular to the basal plane that is comparable to that found for C60, Table 4. Similar arguments can be used to explain the range of bulk modulus values found for the three crystalline forms of carbon. Diamond has the highest known thermal conductivity of any material. The thermal conductivity of graphite is much higher than that of copper in the basal plane, but the value perpendicular to the basal plane is low. The thermal conductivity of C60 is very low.

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