Durability of cordierite honeycomb structure for automotive emission control
Ceramic (cordierite) honeycomb structures are employed in the automotive industry for trapping and incineration of particulate material from the exhaust gases of diesel-powered cars. The most diffuse pollutants present in the particulates are sodium, lead, iron, calcium, zinc and vanadium: they can react with cordierite during regeneration of the filter. In this paper, the short-term interaction of these pollutants as oxides with cordierite filter was studied to examine the consequences on the ceramic characteristics, using differential dilatometry, coupled to X-ray diffraction (XRD) and scanning electron microscopy (SEM). These investigations demonstrate that pollutant ions diffuse into the cordierite lattice, modifying its thermal expansion behaviour, often leading to surface etching and formation of new phases. Some of these new phases present a thermal expansion coefficient that is higher than that of pure cordierite one: different local dimensional variations in the ceramic structure lead to the appearance of microcracks. Sodium and lead oxide are the pollutants that most affect the lifetime of cordierite filters.