CeraMat

Today, cordierite plays a very important role in the reduction of noxious substances emitted from internal combustion engines. Honeycomb structures with parallel channels offer a good solution as supports for catalysts at an acceptable counterpressure. Porous ceramic materials permit an efficient mechanical filtration of carbonaceous particles contained in the exhaust gases of diesel engines, which are forced to flow through the walls.

This paper compares Al2O3-ZrO2 composites obtained from the same powder precursors dried by two different methods: spray drying and alcohol extraction via sol-gel route. The composite with 15% ZrO2 obtained by sintering microsphere powders produced via a sol-gel method exhibited better mechanical properties.

Crystalline powders of Li2ZrO3 were prepared by gelling ZrCl4 and CH3COOLi with NH4OH at 50 °C, at different pH values (5, 7 and 8) and for different times (3, 12 and 24 h), then drying and calcining. Compacts from these powders were found sinter to higher densities than a commercial Li2ZrO3; their porosity at 1200°C was close to 3 μm and was suitable for blanket material applications. Tritium release as HTO begins at 300 °C and reaches 73% at 400 °C, a temperature much lower than that required for Li2O.

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.

The characterization of three microcystalline Y2O3-stabilized tetragonal zirconia (t-ZrO2) preparations was carried out by BET, XRD, HRTEM, and FTIR spectroscopy, and revealed that morphological and surface features of t-ZrO2 specimens depend, much more than in the case of the monoclinic modification (m-ZrO2), on the preparative history of the material.

Two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol% Y2O3 have been characterized, and their features compared with those of a 2 mol% t-ZrO2 preparation and of a monoclinic zirconia (m-ZrO2) preparation. At ambient temperature, CO adsorption occurs only on surface cationic Lewis acid sites located in crystallographically defective configurations. The various t-ZrO2 preparations present several types of such defective sites, depending on the temperature of the sintering stage.

The durability of cordierite honeycomb structure for automotive emission control is deeply affected by the presence of some pollutants (Na2O, CaO, ZnO, PbO, Fe2O3 and V2O5) on the trap walls during the high-temperature step of filter regeneration. The long-term interaction between cordierite and the single pollutant oxides as well as the interaction between cordierite and some binary pollutant mixtures as a function of temperature have been investigated by differential dilatometry, X-ray diffraction and scanning electron microscopy (SEM).

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.