Isostatic Strength of Porous Cordierite Ceramic Monoliths

The isostatic strength of porous cordierite ceramic monoliths plays an important role during canning and subsequent operation of automotive catalysts. Its value depends on wall porosity, cell geometry, skin thickness and morphology, monolith size and contour, and substrate/washcoat interaction. If the stresses induced by canning loads and closure speeds exceed the isostatic strength, the monolith may exhibit either crushing or shear type failure.

This paper presents the room temperature isostatic strength data for coated and uncoated ceramic monoliths of different contour, size, and cell geometry. The applied isostatic load on the monolith is translated into stresses in the porous cell wall using both an analytical model and finite element analysis. It is found that the failure criteria are governed by the fundamental tensile and compressive strengths of the cell wall. The addition of alumina washcoat increases the isostatic strength as long as the substrate/washcoat interaction is carefully controlled during the coating process. The higher isostatic strength of coated monoliths facilitates the canning process and permits higher holding pressure, thereby enhancing their physical durability over the specified lifetime of the vehicle.