A novel technique for quantifying the cohesive strength of washcoat

The washcoat used as the catalyst carrier in catalytic converters is designed to enlarge the contact area between exhaust gas and catalysts. The cohesive and adhesive strength of a washcoat layer is therefore highly important for the service life of catalytic converters. However, in the present literature, there is no direct method to measure these strengths distinctively. Given the current knowledge gap, this paper was written to present a novel technique which was able to separately quantify the cohesive strength of a washcoat layer based on stress measurements. In this method, a washcoat sample made of wet-milled γ-alumina was formed in the shape of a tablet. The cohesive strength of a washcoat layer can be obtained by measuring the tensile strength of these tablets. The tablets prepared using a suspension with pH higher than the isoelectric point of γ-alumina and under low drying rates were found to be the strongest. The reason behind this observation was determined to be that at high pH the particles in suspension were more mobile to travel to favourable packing sites, to form a layer, and low drying rates granted more time for the packing to complete. The fact that the cohesive strength obtained can be logically explained supported the validity of the new method.