Effect of Porosity on the Response of Alumina Thick Films towards Moisture

In this work, porous thick films of α-Al2O3 and γ-Al2O3 ceramic materials have been investigated as moisture sensitive materials. The thick film of synthesized α-Al2O3 was sensitive to a wide range of relative humidity (10%-95%), while γ-Al2O3 thick film with controlled micro and nano porosity was found to be effective in the detection of low concentration moisture, viz.1-100 ppm. The tape casting of α-Al2O3 and gel casting of γ-Al2O3 were carried out using organic additives and pore former additives, respectively. Characterization of the synthesized materials was executed using X-ray diffraction, field emission scanning electron microscopy, atomic force microscope and Brunauer-Emmett-Teller surface area analysis. The important parameters like humidity sensitivity, response and recovery time which determine the efficiency of the thick film sensors were found to be influenced by the microstructure of the final films. Pore size distribution and surface area of the films were examined by Hg intrusion porosimetry and BET techniques as both of these properties play an important role in moisture sensing. The developed sensors exhibit significant sensitivity to moisture (humidity) and long time stability which are essential for device application. These sensors are applicable in various industrial and medical fields