Application of the Zisman critical surface tension technique to ceramic surfaces at high temperature

The critical surface tension technique is one of many possible approaches that can be used to determine the energy of ceramic surfaces at high temperature. Although it has been shown to agree with other techniques used at low temperature, previous attempts at high temperatures have failed. This study is the first to use this technique successfully at high temperatures. It was accomplished by (1) carefully avoiding bulk oxidation and liquid-solid reactions and (2) using high purity, homologous, high-temperature liquids. High-purity Group IIIA metals form the homologous series of liquids used for characterizing single crystals of α-Al₂O₃. Experimental conditions were controlled to produce sessile drops that had submonolayer oxide films on the liquid metal. The results for oxygen-saturated, liquid-solid interfaces yield an average value of 1590 mJ/m² for the surface energy of {0001} and {1120} surfaces of sapphire at 1073K. These results are in excellent agreement with prior measurements of the surface energy of Al₂O₃ over a wide temperature range using other techniques and low-temperature static lattice simulations.