Development of Zr/ZrO2 high temperature and high pressure sensors for in-situ measuring chemical parameters of deep-sea water

Abstract

In order to in situ measure chemical parameters of deep-sea water and hydrothermal fluids at mid-ocean ridge (MOR), it is necessary to use high temperature and high pressure chemical sensors. Developing new sensors is essential to measure in-situ pH and other chemical parameters (dissolved H2, dissolved H2S) of deep-sea water and hydrothermal fluids in a wide temperature range (2°C–400°C) at MOR vents. The YSZ (Yttria Stabilized Zirconia, 9%Y2O3) ceramic-based (HgO/Hg) chemical sensors possess excellent electrochemical properties at high temperatures, which have been used to measure chemical parameters of hydrothermal fluids above 200°C. A novel Zr/ZrO2 oxidation/reduction electrode was constructed by oxidation of Zr wire in Na2CO3 melt. This Zr/ZrO2 electrode has good chemical stability while measuring pH of high-temperature aqueous solutions, combined with a Ag/AgCl reference electrode. Potentials of the Zr/ZrO2 sensor in association with a Ag/AgCl reference electrode vary linearly with pH over a wide pH range, as tested by various NaCl-HCl-H2O solutions (NaOH-NaCl-H2O for basic solutions), at temperatures in the range of 20°C–200°C. Thus, the Zr/ZrO2 sensors can be utilized in monitoring the fluids over the temperature range of 2°C–200°C. The Zr/ZrO2 electrode combined with Ag/AgCl, Ag/Ag2S, and Au electrodes has been used to measure pH and other chemical parameters (dissolved H2, dissolved H2S) of aqueous fluids from low to high temperatures and high pressures in the laboratory and to monitor those parameters of deep-sea water in South China Sea.