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Active elements for humidity sensors based upon MgAI,O, thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO, substrates by radiofrequency (rf) sputtering. Sintered MgAI20, pellets were prepared by traditional ceramic processing. Scanning electron microscopy (SEM) analysis showed that the thin films were rather dense and homogeneous, made up of clustered particles of about 20-30 nm, while the pellets showed a wide pore-size distribution. X-ray photoelectron spectroscopy (XPS) demonstrated that the thin films have a stoichiometry close to that of MgAI,O,. Sintered MgAI,O, is crystalline, while it is disordered in thin-film form. The presence of two different components of the Al 2p peaks was correlated with the structural difference between pellets and thin films. The relationship between good film-substrate adhesive properties and the chemical composition at the interface was studied. The electrical properties of the sensing elements were studied at 40°C in environments at different relative humidity (RH) values between 2% and 95%, using ac impedance spectroscopy. MgAI,O, thin films showed interesting characteristics in terms of their use in humidity-measurement devices. Resistance versus RH sensitivity values showed variations as high as 4 orders of magnitude in the RH range tested for thin films, and 5 orders of magnitude for pellets.The differences in the electrical behavior of MgAI,O, pellets and thin films were correlated with their different microstructures.

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Hydroxyapatite (HA) nanopowders were synthesised following two different precipitation routes: (a) from calcium nitrate and diammonium hydrogen phosphate solutions and (b) from calcium hydroxide suspension and phosphoric acid solution. The influence of precipitation process, concentration, and synthesis temperature on HA particle size and morphology, phase composition, thermal stability, and sintering behaviour was investigated by means of: thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron microscopy (TEM, SEM) and dilatometry

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