Modified CVD of nanoscale structures in and EVD of thin layers on porous ceramic membranes

Experiments on the modified chemical vapour deposition (CVD) and the electrochemical vapour deposition (EVD) of yttria-stabilized zirconia on porous substrates are reported. It is shown that, in the CVD stage, deposition occurs in a small (<20 um) region at the edge of the substrate, very likely leading to pore narrowing. This result illustrates the feasibility of the CVD technique for the modification of ceramic membranes to the (sub)nanometer scale. Film growth in the EVD stage is shown to be controlled by the inpore diffusion of the oxygen source reactant for short (<5 h) deposition times. The yttria to zirconia ratio in the deposited film is determined by the ratio present in the vapour phase. Very thin (<2 um) films can be deposited, which have a potential application in solid oxide fuel cells

On the kinetic study of electrochemical vapour deposition

A theoretical analysis is presented which quantitatively describes the transition behavior of the kinetics of the electrochemical vapour deposition of yttria-stabilized zirconia on porous substrates. It is shown that up to a certain deposition time and corresponding film thickness the rate limiting step is oxygen diffusion through the substrate pores, giving a linear dependence of the film thickness on the deposition time. For longer deposition times, i.e. thicker films, a transition of the rate limiting step to bulk electrochemical diffusion in the film occurs, resulting in a parabolic dependence of the film thickness on the deposition time. Simulation results are presented to show the effects of the experimental conditions on this transition time

Evaluation of porous ceramic cathode layers for solid oxide fuel cells

Sr0.15La0.85MnO3 layers with 2 and 10 u thickness, deposited on zirconia based electrolytes, were evaluated as cathodes for high temperature applications. Different electrode layers were characterized in terms of thickness, porosity, three phase boundary line per unit area (TPBL), and concentration polarization behavior. Electrodes with maximum porosity and TPBL exhibit minimum concentration polarization losses at constant current density

A Kinetic Study of the Electrochemical Vapor Deposition of Solid Oxide Electrolyte Films on Porous Substrates

The electrochemical vapor deposition (EVD) method is a very promising technique for making gas-tight dense solidelectrolyte films on porous substrates. In this paper, theoretical and experimental studies on the kinetics of the depositionof dense yttria-stabilized zirconia films on porous ceramic substrates by the EVD method are presented. The more systematictheoretical analysis is based on a model which takes into account pore diffusion, bulk electrochemical transport, andsurface charge-transfer reactions in the film growing process. The experimental work is focused on examining the effectsof the oxygen partial pressure and substrate pore dimension on the EVD film growth rates. In accordance with thetheoretical prediction, the pressure of oxygen source reactant (e.g., water vapor), the partial pressure of oxygen and substratepore dimension are very important in affecting the rate-limiting step and film growth rate of the EVD process. In thepresent experimental conditions (e.g., low pressure of oxygen source reactant and small substrate pore-size/thicknessratio), the diffusion of the oxygen source reactant in the substrate pore is found to be the rate-limiting step for the EVDprocess