Effect of pore structure, randomness sand size on effective mass diffusivity

The effective mass diffusivity <D-m> of large specific surface area catalytic porous coatings is analyzed rising 2-D network models of connecting arms and verified experimentally for a multiple pore length scale coating layer. The network model includes effects of variation in the lattice randomness (Voronoi tessellation in the form of Delaunay lattice triangulation), pore coordination,number, pore size (Knudsen effect), and pore-size distribution on the predicted <D-m>. The effect of pore poisoning resulting in a pore blockage, is analyzed. Correlations,for the porosity and pore-blockage dependency of <D-m>, as well as relationships for the pore size (low-dimensionality) and multiple pore length scale effects, are also discussed. An experiment performed on a catalytic converter washcoat segment (represented by three pore length scales) placed on an otherwise impermeable wall of an electrochemical sensor shows a good agreement with the predicted <D-m> based on a multiple pore length scale medium with parallel diffusion paths.