DETERIORATION OF CORDIERITE HONEYCOMB STRUCTURE FOR DIESEL EMISSIONS CONTROL

The durability of cordierite honeycomb structure for automotive emissions control is strongly affected by the presence of some pollutants on the trap walls during the high temperature step of filter regeneration. The short-term interaction between cordierite and some single pollutant oxides (Na2O, CaO, ZnO, PbO, Fe2O3, V2O5) has been investigated by differential dilatometry, XRD, IR spectroscopy and SEM. There is evidence that the pollutant ions diffuse into the cordierite lattice. The formation of new phases and surface etching have often been observed, the appearance of new phases having a thermal expansion coefficient different to that of the pure cordierite is responsible of a diffuse microcracking, particularly in the sample polluted by sodium oxide. At 900-degrees-C all the pollutants except Fe2O3 strongly etch the cordierite; particularly dangerous is the presence of sodium or lead oxides which are able to completely destroy the cordierite structure.