| Because CO can react easily with O2 in accurate quantity, the concentration ofCO in Oxygen-Containing gas system can be analyzed by Zr02 Oxygen sensor. Aseries of measurements had been done really. The working temperature of the sensorand the flowing velocity of the gas, which effected the measurement, wereemphatically studied. A sensor having definite constituent showed particularresponse to (0, + CO) mixed gas system among broad temperature range. We canselect the most appropriate temperature to measure it. The sensor was made fromY203 stabilized Zr02 (YSZ) in which Y2O3 owns mo18%. By ascending temperaturein procedure, we observed that the sensor responded to all kinds of (02+CO) mixedgas when temperature rose to 750, so was the most appropriate temperature. Wetested the function of the sensor at different flow rate. The data reappeared at lowvelocity and the catalytic oxidation of CO proceeded more deeply at low flow rate.The most appropriate velocity was the easy-flow-rate, which the gas flowed at150mL/min under 1 atm. 02 molecules adhering to the Pt electrode acceptedelectron from Pt, then O2- was yielded. The process that 02 changed into O2- wasconnected with the temperature. Obviously, not all the O2 molecules were activatedat the same time. The 02 molecule, which was'absorbed tightly on the.site of Ptwhere O2 and Pt were excited enough by heat, was prior to be activated. Becausemoving gas molecule had equal chances in all direction, low oxygen content gassystem had less' activated oxygen when the temperature was defined. The sensorresponded to low oxygen content gas system at higher temperature meanwhile thesensor responded different potential to different mixed gas at the same temperature.The gas samples (CO content is among 4-19%) were also measured by Orsat analyzing apparatus to evaluate the accuracy of the method. It demonstrated that the results of the two methods were in good agreement with each other and the relative deviations were below 2.9%. The min deviation was 0.1%. So the method which CO was measured by ZrO2 oxygen sensor was accurate and feasible. The adsorptionmechanisms which O2 and CO was adsorbed on Pt electrode / the surface of ZrO2 material / the three phase boundary were studied. The reaction mechanism at the adsorption site was also discussed. CO gas reacted with 02 gas in the gas phase, the competitive adsorption between CO molecule and O2 molecule which took place at the TPB, C0(ad) reacted with O(ad) or O2, The three processes constituted relative equilibrium. The electrochemical potential of the electrode reflected the components of the mixed-gas. The potential of the electric cell was a mixed-potential, threematrixes constituted the total value: E = 6O2 .EO2 + 6CO . Eo + 6CO ?Ka ?Eco Themethod was especially suitable for the high temperature system.Two kinds of catalyst (Pt-Al2O3 and CuO-Al203) were used in the catalytic-Oxidation to make CO be oxidized completely, the performance of the two kinds o: catalyst were compared. The mechanism of the catalysis was also discussed. Tb. experiments indicated that the catalytic efficiency of Pt was higher than that of CuO. CO was oxidized more deeply by using Pt-Al203 and the sensor appeared more stablely. The adsorption between CO and Pt (or CuO) played a valid role in the catalysis.After a long period that CO acted on the sensor, not only the construction of tht sensor but also the constituent of the sensor had been changed by CO, of course the performance of the sensor must have been affected. CO can react with ZrOj-Y solid electrolyte under high-temperature environment. This would influence tht phase and the constituent of the material. The electroresistance rose, the electroconductivity dropped, the activation energy also increased. The electroconductivity of the Pt electrode dropped, the relationship between the electroconductivity and the temperature didn't fit the Arrhenius equation. |
PDF Full Text Request