Critical surface energies of Al2O3 and graphite

Based on the wetting properties of a ‐Al 2 O 3 , 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/cm 2 ) of the (0001) surface of a ‐Al 2 O 3 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.