Determination of low chlorine concentrations in air using semiconductor chemical sensors

Comparative studies of electophysical gas-sensitive properties of semiconductor metal oxides (NiO, WO3, and In2O3) in detecting trace concentrations of chlorine in air at 250-300 degrees C were performed. WO3 and ln(2)O(3) film sensors were found to have the best sensitivity, selectivity, and stability. However, WO3 films are characterized by a longer relaxation time (3 min) compared to In2O3 films, for which it is no longer than 30 s. The kinetic and steady-state relative conductivity values of In2O3 films as functions of the chlorine concentration in air fall on the same curve in the range 0.01-0.7 ppm. This suggests that the concentration of chlorine in air can be determined from the initial rates of the variation of the relative conductivity of films, which significantly decreases the time of analysis (from 40 to 5 s at a sensor working temperature of 300 degrees C). Changes in air humidity in the range from 40 to 80% have no effect on the initial rates of the variation of the relative conductivity of In2O3 films under kinetic conditions. The mechanism of the variation of In2O3 film conductivity in detecting chlorine in air was discussed.