Abstract
A new potentiostatic system has been designed which is capable of controlling and monitoring a large number of specimen electrodes at many different set potentials, all within a single test tank or process stream, for long periods of time. Block diagrams of the potentiostatic control system are provided, together with details of the current measurement subsystem and power supply. In order to assess the performance of this system, cathodic Tafel plots were obtained with the new system by holding copper wire specimens in flowing sea water at eight different cathodic potentials for up to 8 days. The results were in surprisingly good agreement with Tafel plots obtained using conventional potentiodynamic techniques with copper wires that had been freely corroding for the same length of time. Anodic polarisation plots obtained with the new system for copper wire in flowing sea water showed a minimum in the current density at −125 m J(Ag/AgCl) that was indicative of the development of a protective film. In another experiment, replicate specimens of AI SI 316 stainless steel wire, each partially wrapped with flexible polyvinyl chloride to create a crevice, were held at many different set potentials for periods of up to 80 days in flowing sea water. The critical potential, below which crevice corrosion did not develop, was found to occur between 150 and 200 mJ(Ag/AgCl). This potential was at least 270 mV more negative than that determined from a potentiodynamic anodic polarisation plot.
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