For this task, you need either a potentiostat or a galvanostat, able to scan a potential (or current) from a "safe" (i.e. stable passive) region to the pitting region. A wide variety of test methods are cited in the literature, but there are common demands:
The potential (or current) should be varied linearly between two points - usually as smooth as possible. It is rewuired to have stable operation conditions when the current suddenly drops at the change from active dissolution to passivity. It is required to limit the maximum current (in potentiostatic action) in order to avoid destruction of the specimen under test. When starting from the active region, rather high currents may be required to achieve passivation. When , in addition, corrosion current densities are to me determined, the Tafel lines should be lines, no banana - shaped curves: IR - drop compensation may be required. You are occupied with a bundle of other works, so the measurement, once started, should run unattended.A nice solution for this kind of problem might be the use of the PGS 95, with built - in PC - interface, our software CPC and the AVESTA - cell.
The PGS 95 is capable of doing all electrochemical tasks within its limits of ± 1 A maximal current and max. 30 V at the counter electrode,but currents in the passive state can be determined down to the range of some nanoamperes. The built - in scan generator makes it easy to operate- manually or, due to its control-interface - by computer control, and the AVESTA cell is the ideal cell for doing such tests without any problems arising from crevice-formation at the electrode. Some other features make this configuration lovely: The potentiostat by itself has the ability to stop or reverse the scan function as soon as a set current level is exceeded. The cell is connected by a cable combination giving best dynamic results, while connection errors are excluded (nearly, referring to Murphy).