Methods for applying a washcoat and heat treating a ceramic honeycomb, and treated articles

• Main Authors: SEYLER DONNA R, GLASSON THOMAS J, MURTAGH MARTIN J
• Format: Patent
• Language: English
• Published: 04.06.2009
• Subjects: APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TO SURFACES, IN GENERAL; LAYERED PRODUCTS; LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT ORNON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM; PERFORMING OPERATIONS; PROCESSES FOR APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TOSURFACES, IN GENERAL; SPRAYING OR ATOMISING IN GENERAL; TRANSPORTING

A method for treating a microcracked, ceramic substrate is provided that obviates the need for filling the microcracks of the substrate via a passivation step prior to sintering a layer of washcoat to the surfaces of the substrate that may either contain a catalyst, or provide a support layer for a catalyst subsequently applied. In the first step of the method, a slurry of particles of a washcoating composition is applied over the surface of the substrate such that particles of the composition are lodged into microcracks of the substrate. Next, the substrate is heat treated to between about 700° C. and 1300° C. The applicants have discovered that such heat treating not only sets the washcoating particles into the substrate, but also causes the microcracks in the substrate to permanently enlarge as a result of the resistance of the lodged particles of washcoating composition against the walls of the microcracks as they attempt to close as a result of thermal expansion of the substrate. The consequent enlargement of the microcracks advantageously reduces both the coefficient of thermal expansion (CTE) and the modulus of elasticity (Emod) of the resulting substrate without substantially reducing the modulus of rupture strength (MOR) of the resulting substrate such that the thermal shock parameter TSP=MOR/[CTE.Emod] remains substantially the same or is higher. The method is particularly applicable to ceramic honeycomb structures used as catalytic converters in automotive exhaust systems.