Kinetics and morphology of electrochemical vapour deposited thin zirconia/yttria layers on porous substrates

By means of electrochemical vapour deposition (EVD), it is possible to grow thin (0.5-5 µm), dense zirconia/yttria layers on porous ceramic substrates. Kinetics of the EVD process, morphology and oxygen permeation properties of the grown layers are investigated. Very thin (~ 0.5 µm) layers are grown at relatively low temperatures (700-800 °C). Water vapour as reactant enhances the surface reaction rate at the solid oxide/oxygen source reactant interface. A transition occurs from pore diffusion (above 1000 °C) to bulk electrochemical diffusion (below 900 °C) as rate-limiting step for layer growth. The zirconia/yttria solid solution is mainly deposited in the cubic phase; the layers grow in a typical columnar way and are polycrystalline. Oxygen permeation measurements show that the oxygen permeation flux through the zirconia/yttria layers is influenced by the layer thickness, morphology, presence of water vapour and the oxygen pressure gradient over the layer.