Porosity in the substrate of an anode-supported solid oxide fuel cell (SOFC) must be tailored to maximize fuel flow to and byproduct flow away from the active region of the cell. A 3-D analysis of pore networks in aluminum oxide samples, produced using the same thermoreversible gelcasting technique as used for SOFC supports, has been carried out. X-ray computed microtomography (XCT) has been performed in conjunction with researchers at the Advanced Photon Source of Argonne National Laboratory. Image analysis allows for the visualization of the 3-D pore networks (view 1 in figure below), which can be modeled as nodes joined by tortuous pathways (views 2 and 3). The tortuosity of the pore networks, related to the permeability of the material, is determined by calculating the ratio of the true path length to geometric distance (view 4).
The samples are produced using Thermoreversible Gelcasting with a polymeric fugitive filler to induce porosity. 3mm diameter cylinders are imaged using XCT at the APS 2-BM (Francesco DeCarlo, Stuart Stock). The XCT data also allows for the calculation of porosity, pore size and pore size distribution. Tortuosity is calculated by randomly selecting a large number of pathways and measuring the actual path length (abbreviated R, red path in the image) and geometric distance (abbreviated L, blue line in the image) for each; τ=R/L. Another way to calculate tortuosity is to model the permeability of the sample using finite element techniques; tortuosity is then back-calculated. Both techniques have been used and show excellent agreement, however the former method is much less computationally intense.
|
