Alessandro Bachiorrini

Preparation of polycrystalline yttrium iron garnet ceramics

Abstract The production of polycrystalline ceramics from YIG powders, obtained by reacting Y2O3 and Fe2O3 oxides, is a well understood and controlled industrial process. However, methods of production via chemical pathways, such as coprecipitation, possess the advantage that the garnet powder is more reactive and no longer requires prolonged grinding which can affect its purity. In this paper, we will show that the mastering of these two processes enables the production of ceramics possessing good magnetic characteristics for microwave applications.

Fast firing of tiles containing paper mill sludge, glass cullet and clay

The paper describes results obtained in the development of a previous research. We study here, in fast firing, the sintering behaviour and measure some properties of tiles containing a mixture of 60 wt% of paper mill sludge and 40 wt% of glass cullet. The behaviour of this material is compared to those displayed by materials obtained by the same mixture added with 10, 20 and 30 wt% of a natural red clay. In parallel, the same properties are measured also on a reference blend, which is presently used to produce commercial tiles. We show that powders containing 60 wt% of paper sludge and 40 wt% of glass cullet to which 30 wt% of clay is added give rise to materials that display a stable sintering process and have good hardness and strength and therefore could be used for the industrial production of tiles.

New hypotheses on the mechanism of the deterioration of cordierite diesel filters in the presence of metal oxides

Abstract It is well known that the durability of the honeycomb structures made of cordierite, used as filters for diesel exhaust emissions, is affected by some components of the soot which can react with cordierite during regeneration cycles at high temperature (up to 1000 °C). Amongst all the components of the soot, sodium is particularly dangerous because of its destructive effect on the cordierite structure. The interaction between sodium carbonate and cordierite has been studied by means of FTIR spectroscopy and the following statements can be made: even if very slowly, the attack on cordierite has already begun at 500 °C and proceeds very quickly onwards from 600 °C; an amorphous phase is formed at 700 °C; at higher temperature, the amorphous phase crystallizes releasing sodium which, during cooling, reacts with carbon dioxide, yielding again sodium carbonate; this carbonate will act as sodium source in the following thermal regeneration cycles. During this study it has also been shown that the first attack is not determined by the sodium ion diffusion into the pseudo-zeolitic channels of the cordierite lattice.

Interaction between some oxides and cordierite

Abstract Today, cordierite plays a very important role in the reduction of noxious substances emitted from internal combustion engines. Honeycomb structures with parallel channels offer a good solution as supports for catalysts at an acceptable counterpressure. Porous ceramic materials permit an efficient mechanical filtration of carbonaceous particles contained in the exhaust gases of diesel engines, which are forced to flow through the walls. Interest in these components is increasing due to their potential effectiveness; it is therefore important to study the problems sometimes encountered during actual applications. This research considers the interaction between some oxides encountered in practical use and the material itself in order to understand the behaviour of cordierite as a basis for better utilisation; some observations and comments are reported.

Interaction of mullite with some polluting oxides in diesel vehicle filters

Abstract Mullite is one of the most promising substitutes for cordierite as a material for the manufacture of diesel vehicle filters. This study investigated the sensitivity of mullite to chemical attack provoked by some of the oxides present in the particulate of diesel-engine exhaust gases. Filter thermal regeneration conditions were simulated by means of heat treatments between 400 and 1000°C. The following pollutants were used: V 2 O 5 , PbO, ZnO, Fe 2 O 3 , CeO 2 , CaCO 3 and Na 2 CO 3 (the last-mentioned as oxide generators). The results obtained were compared with those for cordierite. Mullite was less sensitive to attack than cordierite but was unable to effectively resist attack by PbO and Na 2 CO 3 .

Elaboration de poudres de yig par coprecipitation

This paper deals with an original method for the preparation of ferrites with the garnet structure by coprecipitation.The different transformations of the coprecipitated hydroxide during heat treatment are studied and reported.YIG crystallization from amorphous oxide is significantly dependent of some parameters.However, pure homogeneous materials can be obtained at low temperature (800–850‡C) for Al substituted YIG Y3AlxFe5−xO12 with 0.5≤x≤1.