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

The preparation of gamma-Fe2O3 by the thermal decomposition of Fe3O4 obtain ed from the hydrazine reduction of ferric nitrate was studied employing dif ferential thermal analysis (DTA), and X-ray diffraction (XRD). Here we repo rt a simple technique that does not need any explosive or high-energy react ions to obtain gamma-Fe2O3. The ethanol sensitivity of pure and Pt doped ga mma-Fe2O3 were investigated by studying the electrical resistance character istics of sensor elements prepared from this material. The Pt doped sensor elements showed a linear response of sensitivity, in the range of 1-1000 pp m ethanol in air, in the logarithmic scale. gamma-Fe2O3 behaves as an n-typ e basic semiconducting oxide when exposed to ethanol vapors and in turn eth anol probably decomposes via the route of CH3CHO to form CO2 and H2O. The m aximum sensitivity after Pt incorporation is found at 175 degrees C. The hi gh 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 an d thr sensor surface. The response time of the elements to 10 ppm ethanol i n air is less than 30 s, Cross sensitivity to other gases like liquefied pe troleum gas (LPG), CO, CH4H2, H2S and NH3 was also studied. (C) 2000 Elsevi er Science Ltd. All rights reserved.