Development of diamond-like carbon-coated electrodes for corrosion sensor applications at high temperatures

Coupled multielectrode array sensors have been used as online and real-time monitors for localized corrosion in both laboratory and field systems. Multiple miniature electrodes made of materials identical to the engineering component of interest are used as sensing electrodes. However, these devices have an upper operating temperature limit of approximately 70 °C because crevice formation between the electrode and the mounting material impairs their performance. In this paper, a crevice-free electrochemical sensor for corrosion monitoring at temperatures above 100 °C is presented. A diamond-like carbon thin film was deposited on the sensing electrodes using plasma immersion ion processing and its properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and laser Raman spectroscopy. The effectiveness of the diamond-like carbon film in protecting the Alloy 22 (Ni-22Cr-13Mo-3Fe-3W) electrodes in a corrosive NaCl–NaNO3–KNO3 salt mixture at 150 °C was demonstrated. The effective corrosion monitoring capability of the new electrochemical sensor at high temperatures was attributed to the pinhole-free microstructure, high electrical impedance, and high corrosion-resistance properties of the diamond-like carbon film.