Critical Surface Energies of Al2O3 and Graphite

Based on the wetting properties of a -Al₂O₃, and pyrolytic graphite by liquid metals, the critical surface energy for spreading was determined and compared with the surface energy of the ceramics. The surface energy γ-₈ (ergs/cm²) of the (0001) surface of a -Al₂O₃ is estimated to be 892–0.12 T (°C), that of the c plane of pyrolytic graphite 1139–0.13 T (°C), and that of the a plane of pyrolytic graphite 1300–0.17 T (°C). Also, the liquid-solid interfacial energies were calculated and found compatible with the values reported in the literature. The surface energy of liquid Ag or liquid Cu is not significantly affected by carbon.