On the effects induced by the accumulation of sodium, iron and cerium, on diesel soot filters

The possible chemical interactions which occur between sodium (as sulphite), iron and cerium (as oxides) coming from pollutants or additives, and the materials which make up three commercial filters, in the working temperature of a Diesel soot filter, were considered. The commercial filters were respectively a cordierite monolith filter, a wound-fiber filter made by continuous Al2O3-B2O3-SiO 2 fibers, and a sintered Chrome-Nickel stainless steel filter plate. Some evidence of the chemical interactions was detected coupling X-ray diffraction (XRD) and Hg porosimetry analyses, scanning electron microscopy (SEM) observations and microprobe investigations. The extent of chemical etching, the involved reaction mechanisms and the possible effects on durability, mechanical performances and filtration efficiency of the filters were also investigated. From the experimental results it was concluded that sodium leads to a diffuse etching of the ceramic filters starting from low working temperatures, and in the case of the metallic filter it induces a negative modification of its porosity. Cerium oxide does not react with the three considered filters: the only interaction consists in a positive effect on the porosity of the metallic filter. Also iron oxide does not give rise to any significant interaction with the three filters.