ZrO2 oxygen and hydrogen sensors: A geologic perspective

The geosciences have been attracted to the high accuracy of 5 ZrO2 cells for both f(O2) and pH sensors. That the very same ZrO2 membrane can be used above 6000C to sense f(O2) and used between 250 and 3000C (maybe higher) to sense pH has been demonstrated. Specific resistivity measurements for such cells follow the equation log R = -2.20 + 4000/T (for T(K) from 298-1573 K) (for Y2O3 levels of 4-8 mol%). In the lower-temperature regime, i.e., pH sensing, the ZrO2 cell does not respond to changes in molecular O2 or H2 in its environment. Geochemical raw material impurities and ZrO2 membrane fabrication techniques that affect f(O2) and pH sensing are discussed. The application of ZrO2 cells to various geologic redox equilibria are demonstrated by a few selected examples