Critical Pitting Potential Experimental Sequence
Run the CPP standard technique by selecting Experiment, DC Corrosion, Critical Pitting Potential from the Framework™ menu bar. This initiates the following sequence of events:
- The Framework creates a Runner window, and the Critical Pitting Potential.exp script is run in this window.
- In the runner window, the script displays a Setup Dialog Box which becomes the active window. This dialog box allows you to view and edit the experiment parameters. Clicking the OK button accepts the parameters and starts the experimental run.
- The script now obtains the use of the Gamry Instruments potentiostat specified during setup, and opens the data file specified in the Output File field of the Setup Dialog Box. If the potentiostat is in use or the data file cannot be opened, the script returns you to the Setup dialog box.
- All header information is written to the data file. Header information consists of the analysis tag, the time and date the experiment was started, and a list of the setup parameters.
- An Open Circuit Delay is performed to determine the "Initial" corrosion potential. The measurement lasts for ten seconds, and the result is written to the data file. The purpose of this Initial O.C.Delay is to establish the Eoc of a fresh specimen surface. We recommended that you start the experiment immediately after immersing the specimen, if you want an accurate initial Eoc.
- A second O.C. Delay is performed to determine the "Final" corrosion potential. This measurement lasts 1 hour by default. You can define the delay in the ECorr Meas. parameters in the Setup Dialog Box.
- The script performs the actual data-collection, starting with a stimulation phase. During this phase, the Stimulat. Pot. is applied to the specimen to "stimulate" pitting. A current-versus-time curve is recorded.
- The script compares the current to the current limit, Limit I, and the change in current to the current rate-of-change limit, I Rate. If either the current or rate-of-change in the current exceeds the limit, the script goes to the repassivation phase. If neither constraint is exceeded, the experiment ends.
- During the repassivation phase, the script switches the potential to the current test potential. A current-versus-time curve is recorded, and the current is checked versus the Limit I parameter. If the current exceeds the limit, the experiment ends, because critical repassivation potential has been reached. If the scan continues for the entire duration without reaching the Limit I current., the script loops back to Step 7, the stimulation phase.
- The next repassivation phase is performed at the next anodic potential that is an integer-multiple of 50 mV.