KINETICS OF THE EVD PROCESS FOR GROWING THIN ZIRCONIA YTTRIA FILMS ONPOROUS ALUMINA SUBSTRATES

The electrochemical vapour deposition (CVD/EVD) method has proven to b e a good technique to form thin, gas tight dense solid electrolyte or mixed conducting films on porous substrates. Applications of the so fo rmed systems are in solid oxide fuel cells (SOFC), oxygen sensors, oxy gen separation membranes and electrocatalytic reactors. In this paper, experimental results on the kinetics of the deposition by the EVD met hod of dense zirconia-yttria layers on porous alpha-alumina substrates are presented, and compared with theoretical models. The experimental work concerns mainly the effect of temperature on the growth rate of the EVD film. At 1000-degrees-C, layer growth occurs linear with time under current process conditions; in this case diffusion of the oxygen source reactant in the substrate pores is the rate limiting step for the EVD process. Between 900-degrees-C and 1000-degrees-C the growth r ate limitation changes to the electrochemical transport through the fi lm, which is parabolic with time. This behaviour is predicted by the t heoretical model.