Microstructure and electrical properties of MgAl₂O₄ and MgFe₂O₄ spinel porous compacts for use in humidity sensors

Among the various materials proposed in the relevant literature, porous ceramic oxides possess suitable characteristics for use as active elements in humidity sensors. Particular attention has been paid to the study of spinel-like oxides, which have also been used in prototype devices, showing good humidity sensitivity in their electrical properties and fast response times. This paper discusses the performance of MgAl₂O₄ and MgFe₂O₄ spinels as sintered porous compacts in terms of their electrical response to relative humidity. The compacts were prepared by forming and sintering powders with different microstructures. The humidity-sensitive electrical properties of the sintered compacts were correlated with their microstructural characteristics, which were determined by means of scanning electron microscopy (SEM), mercury porosimetry, and specific surface area measurements, using the BET method with N₂ as adsorbate.