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The atmospheric pollutant monitoring is a present need that pushes the development of reliable and cheap solid-state gas sensors. Very small concentrations of pollutants are able to dramatically deteriorate air quality, thus atmospheric monitoring methods should be able to evaluate very low gas concentration levels. Aim of this work is to compare the sensing performances of metal-oxides powders obtained by means of sol-gel (SG) and hydrothermal (HY) method. TiO 2 and SnO 2 are two of the most common materials able to sense gases upon variations of their energy barrier. One of the main factors enhancing the detection properties of these oxides is the grains dimension. Sharp increase in sensitivity is in fact expected when the grain size becomes smaller than the space charge width. The work is focused on the different methodology and on the outcome related to the two methods. The properties of TiO 2 and SnO 2 are investigated either as powders or as thick layers, the latter necessary to prepare thick film gas sensors.

In the view to develop a novel class of electroconductive ceramics where the conductive phase is molybdenum disilicide, composites with AlN-SiC-MoSi 2 at 55/15/30 and 60/20/20 vol% concentration respectively were produced by tape casting and sintering. Two compositions were designed in order to tailor the electrical resistivity of functionally graded components, which are constituted by two or more portions of the studied composites. In order to optimise the tape casting process, the non-aqueous ceramic suspensions were investigated controlling binder and plasticizer content and the binder to plasticizer ratio. Compositions of the slurries were related to the green and final density and to the microstructural features of mono and multilayers samples. Controlled debonding and sintering tests were carried out under nitrogen atmosphere at temperatures of 1850°C, with appropriate heating gradients, protecting the samples in a powder bed. Density and microstructure of the sintered samples were examined and correlated to the processing conditions.