Shutaro Machiya

Changes of Internal Stress in Solid-Oxide Fuel Cell During Red-Ox Cycle Evaluated by In Situ Measurement With Synchrotron Radiation

The internal stress in anode-supported solid-oxide fuel cells (SOFCs) was evaluated by in situ measurement using high-energy x-ray synchrotron radiation. The oxidized cell had a compression of ∼400 MPa in the c-ScSZ electrolyte thin film and a tension of 50-100 MPa in the NiO-YSZ anode substrate at room temperature. The internal stress decreased with increasing temperature, becoming approximately zero at 1000 K. Although the internal stress returned to its initial value after the thermal cycle, the stress decreased to ∼200 MPa in the electrolyte after the reduction cycle because of the decrease of the coefficient of thermal expansion mismatch between the electrolyte and anode. The red-ox cycle would be detrimental for anode-supported SOFC.

Analysis of elastic properties of textured thin films

Finite element models of polycrystalline thin films were constructed based on the Monte Carlo method. The models consisted of columnar aggregates of cubic crystals with fiber texture whose axis was direction perpendicular to the film surface. In the Monte Carlo method, the nucleus of a crystal was distributed at positions generated by the random number, and the crystal boundary was formed from the coordinates of the nucleus of crystals by using Voronoi tessellation. The number of grains in a sample volume was varied 10 to 1000, and fifty models with different orientations were produced for each case. A constant uniaxial displacement was applied to the models to examine the scatter of elastic properties of thin films under the conditions of plane strain and plane stress. The scatter and mean values of Youngs modulus and Poissons ratio were obtained as functions of the number of the grains within a sample volume. A method is proposed to determine the number of grains for thin films to have macroscopic properties for various thin films with different degrees of elastic anisotropy.