Ellipsometric porosimetry: fast and non destructive method of porosity characterization of solid oxide fuel cell material based on YSZ thin film

摘要

Spectroscopic Ellipsometry is the technique of choice to characterize thickness and refractive indices of thin layers. Atmospheric Ellipsometry Porosimetry (EPA) measures the change of the optical properties and thickness of the materials during adsorption and desorption of wet air at atmospheric pressure. Concentration of humidity changes at each step of measurement from dry air to saturated air. This non contact and non destructive technique is an effective and unique method to characterize porosity, pore size distribution (PSD) and Young modulus of thin porous films. It does not require to scratch the film, does not need low temperature or low pressure.Detailed description of the technique will be exposed in the paper and several meso-porous films (with pore size larger than 1nm) using the Kelvin formalism will be presented. The porosity of the layer ranges from few percent up to 40%. As it is an optical method, it is non contact, non destructive, fast (down to 15 minutes) and room temperature method. It does require low pressure or any preparation of sample. Solid oxide fuel cell is an electrochemical device that converts the chemical energy in fuels into electrical energy by exploiting the natural tendency of oxygen and hydrogen to react. The cell is constructed with two porous electrodes, which sandwich an electrolyte. Selection of materials for the individual components presents the most significant challenges in this technology. Each material must possess the correct chemical, electrical and structural properties to perform its function in the cell. Yttria stabilized Zirconia, (YSZ) is a suitable material for two of the components in this system: the anode and the electrolyte, where its morphology is notably different for each component. Using EPA technique, it becomes possible to characterize in term of porosity and pore size distribution the morphology of both components made by YSZ. We will show the characterization of material in thin film with different porosity and pore size distribution. Graded porosity versus depth could be also demonstrated and will be shown for the first time on such material.