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 resistant 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 isotropie 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 x-A12O3 is assumed to be responsible for this failure.