Development of oxygen and pH sensors for aqueous systems. Final report

Corrosion science has long recognized that two of the most important parameters in characterizing the corrosivity of an aqueous environment are oxygen chemical potential and pH. These parameters not only determine the thermodynamic driving forces for various corrosion reactions, but also characterize the rates of these reactions and hence the lifetime of a particular component. The primary goal of this project is to develop an electrochemical oxygen and pH sensor for continuous use in the cycle chemistry control of power plants. In the past year, electrochemical sensors with a metal/metal oxide or metal/metal hydride internal reference electrode and a fluoride-based electrolyte tube have been developed and tested in this laboratory. The corrosion tests showed that the LaF{sub 3}-based solid electrolyte was very stable both chemically and physically in water. Furthermore, its electrical conductivity is 4 to 5 orders of magnitude higher than that of stabilized zirconia below 573 K (300{degree}C), which is the main advantage of a fluoride-based electrolyte at low temperatures. With this electrolyte and the selected internal oxygen reference electrode (Ag/Ag{sub 2}O), the electrochemical probe demonstrated Nernstian responses to the oxygen chemical potential and pH of the aqueous solution with good reproducibility. A similar cell with Zr/ZrH{sub 1+x}more » as the internal hydrogen reference electrode showed promising pH sensing characteristics. It is proposed that these two cells be combined to form a double-headed electrochemical probe to determine oxygen chemical potential and pH in the solution simultaneously.« less