Coating process of honeycomb cordierite support with Ni/boehmite gels

This study presents the development of a method for the washcoating of Ni/boehmite gels, prepared by sol-gel process, onto the surface of a commercial ceramic monolith. Indeed, cordierite monolith in honeycomb shape was used as substrate for Ni/Al2O3 deposition. An experimental assembly was made in order to apply the coating on the cordierite surface. Different suspensions were used with various viscosities and multiple coating parameters were tested as the withdrawal speed, or the number of impregnations. It was observed that the simple deposition of the Ni/boehmite gel led to the formation of coating. Different morphologies were observed, and defects were highlights as cracks, coating-free areas or aggregates. Among the various studied parameters, the pH of the sol appeared to play a role even more important than the viscosity. Indeed, the sol acidified with nitric acid showed a coating which was almost free of cracks or of large aggregates. Moreover, the use of a mix of a slurry of calcined alumina particles and of colloidal boehmite appeared also as an interesting path. The beneficial influence of a slurry was attributed to a better resistance of the coating against the stresses induced during drying, and a deviation of the cracks in the gels by slurry grains.