Synthesis and characterization of metal-doped humidity sensors based on hematite for environmental monitoring applications

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Afify, Ahmed S.
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Humidity sensors have several applications in both industrial processing and environmental control. Pure and doped hematite have proved to exhibit a remarkable humidity sensing properties. The aim of this investigation is to study the effect of doping of some metal ions (Li+, Mg+2, Ba+2, Sr+2, and Na+) onto the crystalline hematite and to determine their sensitivity towards relative humidity (RH). The obtained crystalline samples were characterized by particle size distribution, X-Ray Diffraction (XRD) combined with Field Emission Scanning Electron Microscopy (FESEM). Sensors were screen printed onto an α- alumina substrates with platinum electrode followed by Screen printing of doped α-Fe2O3 powders and a binder for the appropriate rheological properties to the paste. After deposition samples were dried in air at room temperature prior to be heat treated at 800°C for 1h. Humidity sensors were tested in a laboratory apparatus made of a thermostated chamber, operated at 25°C, in which relative humidity (RH) could be varied between 0 and 96%. The doped sodium metal ions (Na+) hematite sample showed a significant response towards relative humidity at room temperature.