1999

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.

Recently, the screen printing has experimented a larger diffusion for producing microelectronic devices: resistors, conductors, humidity and gas sensors. Simplicity, versatility and low cost are the most significant reasons for its development and success. It has been applied in several high technology applications, because of its suitability to be printed on different materials; in microelectronics, various functional devices have been realised very competitive, if compared to massive materials.

The preparation and characterization of the properties of mullite ceramic foams suitable for diesel exhaust filtration systems are described. Two foams of different cell sizes, 32 and 61 ppi (pores per inch), were prepared from slurries by the replication process with polyurethane sponges as the templates. The microstructure and the dependence of the porosity and the mechanical properties on the preparation and resulting foam cell size and normalized density are discussed.

The effect of Al2O3 (Saffil) short fibers on the response of 2014-Al2O3(f) composite to thermal treatment was investigated. Composite samples were produced by squeeze casting starting from ceramic preforms of Saffil (13% vol. of fibers). Their behaviour was compared to that of 2014 unreinforced alloy fabricated by squeeze casting as well. The best process parameters suitable for solution of alloying elements were assessed by means of differential scanning calorimetry (DSC) and electron microprobe analysis (SEM-EDS).

Metal vanadates of K, Rb, and Cs and their solid solutions were prepared by reaction between carbonates and vanadium(V) oxide, characterized by X-ray diffraction and tested as catalysts for carbon combustion. These vanadates are all orthorhombic but show different lattice parameters depending on the ionic radius of alkali metals. A complete solubility in the solid state was found to exist for the systems KVO3-RbVO3 and RbVO3-CsVO3, while only terminal solid solutions were found in the KVO3-CsVO3 system.

Pyrovanadates of potassium and cesium were prepared and tested as catalysts for low-temperature combustion of carbon. Their catalytic activity was investigated by both temperature-programmed oxidation and thermogravimetric analysis and compared with that displayed by the metavanadates of the same elements, previously proposed as promising catalysts for soot combustion in diesel emissions. Pyrovanadates show an intrinsic catalytic activity noticeably higher than that of the corresponding metavanadates.

The first stages of the development of a catalytic trap for diesel particulate removal from vehicle exhaust gases are addressed, ranging from catalytic trap preparation (a ceramic foam is deposited with catalysts, suitable for soot combustion, based on mixtures of KCl and different vanadates) to catalytic trap testing in a specific pilot plant (an acetylene burner is used to produce a soot laden flue gas which is then treated by the apparatus while the pressure drop buildup throughout the trap and the trap collection efficiency is measured).