Humidity sensing exclusively by physisorption of water vapors on magnesium ferrite

Water vapor adsorption phenomenon on magnesium ferrite surface has been analyzed by determining binding energy involved in adsorption of water vapor. Activation energy for charge conduction has been calculated by fitting Arrhenius equation using temperature dependent (25-45 degrees C) conductivity data in the range for 0-90%RH. Nominal change in activation energy observed with increasing humidity. Clausius-Clapeyron heat equation has been used to calculate the isosteric heats of adsorption utilizing the equilibrium data of the isotherms measured for 25-45 degrees C. The results have exhibited a decrease in heat of adsorption from 0.14 eV at 10%RH to 0.02 eV for 90%RH. While binding energy computed has been found less than 0.2 eV supporting prominent physisorption of water vapors on porous magnesium ferrite. Also, complete recovery of conductivity values in adsorption-desorption curve confirms the physisorption of water vapors. The electrical conduction mechanism in magnesium ferrite with changing humidity has been analyzed by impedance spectroscopy. (C) 2012 Elsevier B.V. All rights reserved.