DESCRIPTION AND CHARACTERIZATION OF A HYDROGEN-SULFIDE GAS SENSOR-BASED ON CR-2-YTIYO3+X

When heated to elevated temperatures (> 250 degrees C), the chromium titanium oxides Cr2-yTiyO3+x displayed p-type semiconducting behaviour giving a resistance increase upon exposure to reducing gases. The materials show a very strong and fast response to the presence of H2S in air, provided they are first pre-treated with a sufficient concentration of this gas, for a sufficient time, at a sufficiently high temperature. The effect of pre-treatment was permanently to increase the baseline resistance in air. The pre-treatment could be reversed by heating to temperatures greater than 420 degrees C in air, Analysis techniques such as X-ray photoelectron spectroscopy (XPS) and temperature program desorption (TPD) mass spectrometry have attributed the pre-treatment to a modification of the surface of the material by sulfur in the form of sulfate or adsorbed sulfur dioxide. The resistivity response to hydrogen sulfide was found to be square root with concentration (c(1/2)) over a wide temperature range (250-500 degrees C).