Experimental and theoretical constraints on pH measurements with an iridium oxide electrode in aqueous fluids from 25 to 175 degrees C and 25 MPa

摘要

In-situ measurement of pH at elevated temperatures and pressures is of major importance for investigating chemical and biochemical systems in extreme environments. Based on the performance of the newly developed IrO (x) electrode at 25 degrees C, we initiated a series of experiments to test the electrode at elevated temperatures (100 to 175 degrees C) and high pressure (25 MPa). The experiment was carried out in a titanium flow-through reactor. Our results revealed good pH response at 100, 150 and 175 degrees C, with good Nernstian slopes at 100 and 150 degrees C. Although a greater-than-Nernstian response was observed at 175 degrees C, the factors that cause this difference are attributed to the accuracy of calculations of the distribution of aqueous species rather than alteration of the IrO (x) surface. A key problem that may limit applications of the IrOx electrode at elevated temperatures and pressures is the noticeable shift in E degrees during the 175 degrees C (25 MPa) experiments and between experiments with similar conditions at 150 degrees C. The results of tests from 25 degrees C to elevated temperatures provide highly useful information on the reversibility and functionality of the IrOx -pH sensor with implications for the suitability of its use under challenging chemical and physical conditions.