Surface tension of liquid Al-Cu and wetting at the Cu/Sapphire solid-liquid interface

For the study of the interaction of a liquid alloy with differently oriented single crystalline sapphire surfaces precise surface tension data of the liquid are fundamental. We measured the surface tension of liquid Al-Cu contactlessly on electromagnetically levitated samples using the oscillating drop technique. Data were obtained for samples covering the entire range of composition and in a broad temperature range. The surface tensions can be described as linear functions of temperature with negative slopes. Moreover, they decrease monotonically with an increase of aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with a thermodynamic model calculation using the regular solution approximation. Surface tensions were used to calculate interfacial energies from the contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) surfaces of an alpha-Al2O3 substrate. The contact angles were measured by means of the sessile drop method at 1380 K. In the Cu/alpha-Al2O3 system, no anisotropy is evident neither for the contact angles nor for the interfacial energies of different surfaces. The work of adhesion of this system is isotropic, too.