The electrochemical determination of oxygen and combustible components in hot gases

The on-site analysis of high temperature gases is important in the emission control and optimization of combustion and metallurgic processes. The presently available potentiometric sensors have the disadvantages of structural complexity and susceptibility to interferences. To overcome these problems, an electrochemical system of three metallic film electrodes operated in the cyclic voltammetric mode was investigated. Sintered yttria-stabilized zirconia (YSZ) was used as the substrate for the electrodes as well as the solid electrolyte. At various selected potentials, the current strongly depended on the concentration of gaseous oxygen. The current was not limited by the gas diffusion and was, therefore, unaffected by the gas flow. It was demonstrated that the electrode and electrolyte degradation can be considerably retarded by the proper selection of the electrode voltage profile.The developed method of oxygen detection could be adapted for simultaneous measurements of moisture and possibly other combustion products which may be present in a hot gas in addition to oxygen. A metal film resistance thermometer deposited directly on the sensor was found suitable for on-site temperature monitoring.The on-site deposition of thin solid electrolyte films was investigated as means of further increasing the flexibility of this sensing method. A successful electrolyte deposit was obtained with ion beam sputtering technique in a mixture of oxygen and argon. The current output of the sensors that employed the film electrolyte was similar to that of the sensors based on the sintered YSZ, but was somewhat limited by the electrolyte conductivity. The possibility and desirability of integration of the oxygen sensor based on the thin film electrolyte and a combustible gas detector was analyzed. The well-known calorimetric method of combustible gas detection was modified to employ metal film heaters in order to provide an improved compatibility with the new oxygen sensor.