On the accuracy of triple phase boundary lengths calculated from tomographic image data

The triple phase boundary (TPB) length is one of the most important quantities obtainable from three dimensional reconstructions of solid oxide fuel cells that utilize porous composite electrodes. However, the choice of TPB calculation method and the voxelation of the microstructures can lead to systematic errors in TPB estimates. Here, two approaches for calculating the TPB density are compared to investigate how different TPB aspects such as curvature, orientation, and phase contact angles affect the results. The first approach applies a correction factor to the TPB length calculated by simply summing voxel (volume element) edge lengths that are shared between voxels of three different phases. The second approach applies a smoothening technique to the TPB curves. The two methods are compared by calculations on different kinds of artificially generated microstructures and on a real SOFC electrode microstructure obtained by focused ion beam tomography. Results are presented showing how specific aspects of different microstructures affect the TPB length calculation error.