Influence of long-term aqueous exposure on surface properties of plasma sprayed oxides A1_2O_3, TiO_2 and their mixture Al_2O_3-13TiO_2

摘要

The surface properties of plasma sprayed Al_2O_3- and TiO_2-based coating materials were characterized in order to investigate the influence of surface strain and phase inhomogenity. The materials were water exposed up to 8 months. The bulk crystallographic structure, dissolution behaviour, effective charge (zeta potential, isoelectric point), surface compositions and oxidation states were determined. In addition, the properties of the aging solutions, such as conductivity, supernatant pH (point of zero charge), and redox potential, were monitored during aging. It was shown that the materials were stable under aging conditions, but that considerable surface rearrangements, such as dissolution-reprecipitation and surface site redistributions may occur. However, overall only minor changes in surface properties results from this restructuring process.