Experiences with sol-gel bonded high porosity alumina fiber materials for filter applications

Abstract

High porous alumina fiber structures appear promising for hot gas filtration in particular for diesel particulate traps. For this purpose, however, a method is required for manufacturing of stable shapes resisant to the blow-out by the gas flow. The sol-gel process was expected to be the best suited method for fiber bonding to provide the required stability. The main tasks of the development-work were a uniform isotropic fiber-distribution, the adaptation of the sol-gel-process to the application, and the deliberate synthesis of the gel-derived alumina bonding phase. The appropriate fibrous structure was obtained by a repeated filtration of sol/fiber suspensions. The properties of the ceramic binder were adapted by concentrating the sol and/or adding aluminas or aluminium hydroxides. Testing of prototypes with optimized structures has shown, however, that the stability of the structure decreased after thermal load. The thermal fatigue of alpha-Al2O3 is assumed to be responsible for this failure.