Durability of ceramic filters in the presence of some diesel soot oxidation additives

The chemical interactions between sodium (as sulphite), iron and cerium (as oxides), coming from fuel additives, and two ceramic filters, in the working temperature range of a Diesel soot filter, were considered. The filters were a cordierite monolith filter and a wound-fiber filter, made by continuous Al2O3-B2O3-SiO2 fibers, respectively. Using 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 porosity changes were investigated. From the experimental results it was concluded that cerium and iron oxides do not react significantly with these filters, whereas sodium leads to a diffuse etching starting from low working temperatures, by many different mechanisms (solid state diffusion, liquid phase diffusion, evaporation-condensation) as a function of the temperature. However the porosity characteristics of the filters, in terms of total porosity and pore size distribution, were not significantly affected by the described chemical interactions.