Surface and Grain Boundary Energies as well as Surface Mass Transport in Polycrystalline MgO

The sessile drop technique has been used to measure the contact angles, θ, of the liquid metals Ag and Cu in contact with polycrystalline magnesium oxide (MgO) in the temperature ranges 1293-1623 K and 1393-1633 K, respectively, in Ar/4%H2 atmosphere. The measured contact angles indicated non-wetting (θ > 90°). Combination of the experimental results with literature data for non-wetted and non-reactive oxide/liquid metal systems permitted the calculation of the temperature dependence of the surface energy of MgO. Thermal etching experiments in argon atmosphere on the grain boundaries intersecting the surface of the polycrystalline ceramic allowed determining the formed groove angles, ψ, with respect to temperature and time, as well as the grain boundary energy. Grain boundary grooving studies in the temperature range 1473-1773 K showed that surface diffusion is the dominant mechanism of mass transport in MgO.