Surface Free Energies of Two Kinds of Graphite Fluorides, (CF)n and (C2F)n

The surface free energies of two kinds of graphite fluorides, (CF)n and (C2F)n, were estimated from the contact angles of several liquids. The contact angles of water on flaky (CF)n and (C2F)n were 117° and 116°, respectively, being slightly larger than that for poly(tetrafluoroethylene), while the values for tablets of powdery (CF)n and (C2F)n were 143° and 141°, respectively, which indicates that powdery graphite fluoride is hardly wetted by water. From the contact angles obtained, the surface free energies were estimated to be ca. 18 mJ/m2 for both flaky (CF)n and (C2F)n, ca. 2 mJ/m2 for powdery (CF)n and ca. 3 mJ/m2 for powdery (C2F)n. These differences depend on the surface conditions such as the packing of fluorine atoms, the roughness and porosity. From the contact angles for the tablets of (CF)n–polyethylene mixtures, it is suggested that the anode effect in the fluorine or aluminium electrolysis takes place when the surface of carbon anode is partially covered by graphite fluoride.