Abstract
Coupled multielectrode array sensors (CMAS) have been used as real-time monitors for localized corrosion in laboratories and field systems. However, most of these devices have an upper operating temperature limit of approximately 70 °C. At temperatures above 70 °C, crevice formation between the electrode and the mounting epoxy can lead to inaccurate high corrosion rates. In this paper, recent development of a novel, electrochemical sensor for monitoring corrosion of alloys at temperatures above 100 °C is reviewed. Sensing electrodes were made of stainless steel, aluminum, titanium and nickel-based alloys with a diamond-like carbon (DLC) thin film deposited on the sensing electrodes. Electrochemical impedance spectroscopy tests showed that the impedance of the coated wire is higher than 1 megaohm at frequencies lower than 1 Hz, which is approximately 1.5 to 2 orders of magnitude higher than that of the uncoated wires. The effectiveness of the diamond-like carbon film to protect the alloy electrodes was evaluated and demonstrated in corrosive solutions with a pH range of 4 to 10 at 120-250 °C. The effective corrosion monitoring capability of the new electrochemical sensors at high temperatures is attributed to the high electrical impedance and chemical inertness of the diamond-like carbon film.
