| Crevice corrosion, a type of localized corrosion, is one of the most damaging forms of materials degradation. Studies of this process have been limited by the lack of experimental crevice samples comparable to real crevices (with rigorously defined dimensions and geometries), and a paucity of real-time data acquisition inside the crevice during the corrosion process.; Using fabrication techniques developed for integrated circuits (IC) and microelectromechanical systems (MEMS), a satisfactory crevice structure consisting of a crevice former coupled to a metallic crevice substrate has been constructed. Crevice substrates with 1-D arrays of nickel electrodes were also made, which provided in-situ spatial information of corrosion. The experimental corrosion results based on the fabricated crevices were in good agreement with those obtained from computational modeling.; To enable the assessment of the conductivity distribution inside the crevice, a conductometric sensor composed of an array of gold electrodes was integrated into the crevice former. The performance of the conductometric sensor was evaluated by using DC and AC measurements, and the results were consistent with each other. The sensor was calibrated in NaCl solutions by analyzing the relation between the solution concentration and the measured resistance.; A potentiometric solid-state chloride and pH sensor array were incorporated into a crevice former to obtain real-time spatial distributions of chloride concentrations and pH values. Each sensor was composed of an ion-selective electrode, a metal contacting track, and a bonding pad. SU-8 photoresists were patterned to form the encapsulation layer. The fabricated chloride sensor, with a Ag/AgCl sensing electrode, showed appreciable potentiometric responses. The sensor also exhibited good selectivity, reproducibility and stability. Based on the Ag/AgCl electrode, the feasibility of making a junction-free miniaturized reference electrode with photocurable aromatic urethane diacrylate as the sensing membrane by IC compatible technique was demonstrated. For pH sensors, two types of polymers, nonphotosensitive PU/PVA and photocurable aliphatic urethane diacrylate, were used to compose the ion-selective polymer membrane. The feasibility of incorporating pH sensors based on both polymers into crevice was investigated. It was found that the urethane diacrylate polymer based pH sensors were promising and showed acceptable potential responses. |
