Preparation of γ-Fe2O3 by the hydrazine method: Application as an alcohol sensor

Abstract

The preparation of γ-Fe2O3 by the thermal decomposition of Fe3O4 obtained from the hydrazine reduction of ferric nitrate was studied employing differential thermal analysis (DTA), and X-ray diffraction (XRD). Here we report a simple technique that does not need any explosive or high-energy reactions to obtain γ-Fe2O3. The ethanol sensitivity of pure and Pt doped γ-Fe2O3 were investigated by studying the electrical resistance characteristics of sensor elements prepared from this material. The Pt doped sensor elements showed a linear response of sensitivity, in the range of 1–1000 ppm ethanol in air, in the logarithmic scale. γ-Fe2O3 behaves as an n-type basic semiconducting oxide when exposed to ethanol vapors and in turn ethanol probably decomposes via the route of CH3CHO to form CO2 and H2O. The maximum sensitivity after Pt incorporation is found at 175°C. The high sensitivity of the sensor to ethanol can be explained on the basis of a catalytic activity that invokes the acid base properties of the test gas and the sensor surface. The response time of the elements to 10 ppm ethanol in air is less than 30 s. Cross sensitivity to other gases like liquefied petroleum gas (LPG), CO, CH4, H2, H2S and NH3 was also studied.