CeraMat

Two mullite powders, different in chemical and morphological characteristics, were compared with respect to their sinterability. For the development of a low-cost sintering step, MgO was added as sintering aid and its content was optimized for both mullites: the enhancement in sintering was imputed to a liquid phase formation. The two mullites presented a strongly different sinterability; the one gave rise to high density sintered bodies while the other, even after a grinding step which made its particle size distribution similar to that of the first, did not reach high final density.

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.

A case history of a severe degradation of concrete foundation plinths and piers of an about-35-year-old building located in Northern Italy is described. Significant amounts of gypsum, near ettringite and/or thaumasite were detected by X-ray diffraction analyses performed on ground concrete samples. Large gypsum crystals were mainly located at the interface between the cement paste and aggregates, as observed by scanning electron microscopy coupled to energy-dispersive spectroscopy microanalysis.

The oxidation behaviour of LnSiAlON (Ln=Y, La) glasses was studied at different temperatures (990–1150 °C) and under different water vapour pressures (360–2690 Pa). These results were also compared with those obtained under O2, N2/H2O or O2/H2O mixtures. When glasses are treated under a N2/H2O mixture, optical and SEM observations show porous scales. Transformations of the reaction rate data and a kinetic model show that there is only one limiting process occurring during oxidation. This rate limiting step is the progress of the chemical reaction at the internal interface.

By using a wet chemical route, pure calcium hexaluminate (CA6) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450°C, has shown a superposition between sintering shrinkage and expansion related to CA2 formation, an intermediate phase formed during calcination and phase evolution to CA6.

Interactions between β-Al2O3 and a sodium aluminosilicate conductive glass, after thermal treatment at 900 °C, have been investigated on screen-printed gas sensors. Due to the high level of glass additions, the starting powder made of β/β″-alumina, underwent strong compositional modifications. SEM and TEM imaging, coupled with chemical analysis, evidenced the formation of nepheline and α-Al2O3 at the interface between β-Al2O3 and the glass.

17th century stuccos located in The Valentino Castle in Turin (Northern Italy) have been studied by means of XRD, TG-DTA, Hg porosimetry and SEM coupled with EDX chemical analysis in order to understand their composition and the degradation causes. The investigated un-degraded samples were made of gypsum, hydrated lime and other carbonates phases on the external surface and up to ca. 20 mm in depth but the compositions were highly heterogeneous.