CeraMat

Recent progress in the development of a β-alumina gas sensor for automotive applications is reported. The sensing device consists of two solid electrolytes (namely a thin film of sodium sulfate deposited on β-alumina by appropriate treatment in a gaseous atmosphere), with two electrodes having different catalytic properties, one made of platinum, the other of gold. The β-alumina component was prepared as sintered pellets by pressing and as thick films by screen-printing.

Ceramic foams show a significant potential of development and application, essentially due to the emergence of environmental preoccupations. A brief overview of the state of the art in cellular ceramic application, preparation and characterization is presented in order to introduce some new data concerning the elaboration of mullite and PZT foams by a replication and a bubble generation method, respectively.

The preparation of NASICON powders has been achieved by sol-gel methods. The precursor solution was either rapidly hydrolyzed, to get a precipitate, or slowly gelated under exposure to atmospheric humidity. The slow hydrolysis process was studied using nuclear magnetic resonance (NMR) spectroscopy in liquid phase. Two-dimensional experiments indicate the occurrence of ligand exchange reactions in solution. Monodimensional 1H, 13C, 31P, and 23Na NMR spectra were also measured. NMR allowed us to follow the advancement of the reaction and determine the degree of polymerization.

NASICON powders having the Na3Zr2Si2PO12 composition were prepared using a sol-gel method. All the reagents used were alkoxides. The precursor solution was rapidly hydrolized in order to get a precipitate, or slowly gelated under exposure to low atmospheric humidity. The slow hydrolysis process was studied using nuclear magnetic resonance (NMR) spectroscopy in liquid phase. 1H, 13C, and 31P NMR spectra were performed. NMR allowed us to identify the advancement of the reaction and the degree of polymerization.

Low-load indentation experiments have been performed on electrophoretic-deposited films of SiC particles on a graphite substrate. Films with thicknesses between 60 and 300 μm prepared at two current intensities and subsequently dried under different humidities were indented with spherical indenters with nominal radii of 10, 50, and 150 μm. Force-displacement data were analyzed to determine contact pressure and elastic modulus versus depth results.

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.

Powders and pellets of new NASICON compositions have been synthesized using a mixed inorganic-organic sol-gel synthesis, by the preliminary formation of a pre-hydrolized TEOS xerogel. The investigated compositions can be described by the general formula Na3Zr2-(x/4)Si2-xP1+xO12, obtained by keeping the Na concentration constant (= 3) at the optimum value reported for ionic conductivity, with x = 0 (the usual NASICON composition), 0.667, and 1.333. The xerogels were calcined at various temperatures in the range 400-1200°C.

The sinterability of two industrial mullite powders, in the presence of MgO as a sintering aid, was investigated. A glassy phase, which was generated during preparation, was present in both powders; this glassy phase had a strong influence on sintering, depending on its content, composition, and spatial distribution. MgO promoted sintering in the presence of a liquid phase, both in the as-received materials and in samples washed with HF, in which most of the pre-existing glassy phase was eliminated.