Abstract
A lasting and sustainable reference electrode is indispensable to analyzing the electrochemical behaviors of metal materials under supercritical state and identifying the related electrochemical parameters. Another technique is to simulate a supercritical water (SCW) circulation system in which the temperature and pressure is greater than 374 ℃ and 22.1 MPa. This study uses Ag/AgCl reference electrodes and Zr/ZrO2 reference electrodes to measure the electrochemical corrosion potential (ECP) of 304L stainless steel in a SCW environment. Experiment results show that at room temperature, under saturated potassium chloride solution, the potential difference between Ag/AgCl reference electrodes made of Zirconium dioxide tubes and commercial Ag/AgCl reference electrodes after 72 h is less than 10 mV, proving that the former are functional at room temperature. Afterwards we measure the ECP of 304LSS and Inconel 625 specimens under 8.3ppm of dissolved oxygen while changing the test temperature from 300℃ to 600℃. As a result the ECP tend to increase with elevated temperature at subcritical environment, but decrease severely with elevated temperature at supercritical environment. In addition, a test including 304LSS and Inconel 625 specimens at constant temperature of 385℃ and 400℃ while changing the dissolved oxygen from deaerated, 300ppb, 1ppm, 8.3ppm, 32ppm was also conducted. The outcome shows that under supercritical environment, ECP changes much heavily in low dissolved oxygen condition than in high dissolved oxygen. At last, we successfully discover the alignment value for Zr/ZrO2 reference electrode to convert its value into SHE value under different temperature with the aid of Ag/AgCl reference electrode.