1994

Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests.

Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests.

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.

The proposed materials and the production process for particulate traps, used in order to reduce the diesel engine emissions, are reviewed. The filter regeneration principles are discussed. An overview is given on the use of catalysts for the NOx reduction or for particulate oxidation in diesel exhaust gas.

Interfacial reactions in Ti-6Al-4V/SiC Sigma fibres (coated with carbon and TiB2) were studied at different temperatures (600, 700 and 1000 °C). Interface microstructure was investigated by scanning electron microscopy and Auger electron spectroscopy. A simulation of the chemical phenomena occurring at the interfaces was carried out using powders of pure titanium, carbon and TiB2; the reaction products were identified by X-ray diffraction. The double coating of Sigma fibres is effective in delaying detrimental reactions with the matrix.