Multiplexed Potentiodynamic - Setup Parameters

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Multiplexed Potentiodynamic - Setup Parameters

Description

 

5 - Multiplexed Potentiodynamic

 

Parameter

Description

Units

Pstat

Select the potentiostat/galvanostat to perform the experiment. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used.

 

Gamry tip bulb

Only potentiostats that are paired with a Multiplexer can be selected.

 

Channel

There is one Channel Setup switch for each of the 8 channels. Click the checkbox to select a specific channel. As the script loops through the channels, it only runs tests on channels that are selected. The selected channel numbers do not have to be continuous.

 

Identifier

A string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs.

 

The Channel Identifier string is virtually identical to the Test Identifier string. The only difference is that in multiplexed tests, the Identifier refers to an experiment run on a single cell and not to the entire experimental run.

 

System

Select a set of electrochemical parameters relevant to your particular test system. The parameters are recovered from the system parameter database file. The recovered parameters are all used for the calculation of the corrosion rate. They are the sample's equivalent weight, density, anodic β and cathodic β. When you attempt to run an experiment, the system searches the SYSTEM.SET file for a parameter set stored under the name in the System parameter. If the software finds no parameter set, an error message appears and you are returned to the Setup dialog box.

 

Area

The electrode area that is used in calculations. It can be set individually for each channel.

cm2

Notes

Enter several lines of text that describe the experiment. There is a separate entry for each channel in a multiplexed test. A typical use of Channel Notes is to record the experimental conditions for a data set.

 

The Channel Notes controls are similar to the Notes control described for non-multiplexed experiments.

 

Base Filename

Each channel has its own data file. The Base Filename is used to derive the filenames for these files. The filename for Channel N (1–8) is created by appending the character N to the Base Filename, then adding a *.DTA filename extension.

 

If the Base Filename is MYMUXDATA, the data file for Channel 1 is named MYMUXDATA1.DTA. The filename resulting from the concatenation of the Base Filename and the channel number must adhere to Windows® filename conventions. Avoid punctuation characters (the underscore, "_", is OK). You are allowed a maximum of 250 (not 255) characters in the Base Filename. The extra characters are reserved for the channel number appended to the Base Filename. Do not include *.DTA when specifying the Base Filename. It is automatically added when the full data file name is generated.

 

Initial E

The starting potential of the potential sweep during data acquisition. The allowed range is ±10 V with a resolution of 0.125 mV. Its accuracy is determined by the settings of Initial E and Final E.

Gamry tip bulb

The Scan Range, defined as the absolute value of Final E minus Initial E, must be less than 8 V.

volts (V)

Final E

The final potential of the potential sweep during data acquisition. The allowed range is ±10 V with a resolution of 0.125 mV. Its accuracy is determined by the settings for Initial E and Final E.

volts (V)

Scan Rate

The speed of the potential sweep during data acquisition.

 

A practical bound on the Scan Rate is 5 mV/s. Higher Scan Rates may run but yield unreliable data because the potentiostat's compensation and filtering are set for long time constants. Custom scripts may allow Scan Rates of 1 V/s or more. A lower bound on the Scan Rate is the minimum Step Size divided by the longest Sample Period. For scans shorter than 2 V, the slowest Scan Rate is 52.1 nV/s or 0.1875 mV/hour. Multiply these limits by four for scans longer than 2 V.

mV/s

Sample Period

The spacing between data points. The shortest Sample Period we recommend is 0.1 s. The longest Sample Period allowed is 715 s for Reference potentiostats and 750 s for Interface potentiostats.

 

Use Sample Period to determine the Step Size of the staircase ramp and the Number of Points in the data curve. Sample Period specifies the length of a step. The height of a step depends on both the Scan Rate and the Sample Period. You can calculate the Step Size and the Number of Points in the scan from:

 

 

 

The Step Size is rounded to the resolution of the D/A converter making the steps. The resolution of the D/A converter is dependent on the type of potentiostat you are using. Consult your potentiostat manual for more information. The default Step Size for a Reactivation scan is 1 mV/step. If the Step Size has to be rounded to fit the resolution of the D/A converter, the Sample Period is also adjusted so that the Scan Rate is correct. The Number of Points must be less than 262 143 (218 - 1). If you have more points, the experiment aborts just before the scan phase of the sequence.

seconds (s)

Conditioning

You may condition the electrode as the first step of the experiment, e.g., to remove an oxide film from the electrode or to grow one. Conditioning ensures that the metal sample has a known surface state at the start of the experiment. This step is done potentiostatically for a set amount of time.

 

Turn the conditioning phase On or Off with the Conditioning switch check box. Conditioning E is the potential applied during the conditioning phase of the experimental sequence. The conditioning potential has an allowed range of ±8 V. The resolution is 0.25 mV. If you have iR-compensation enabled for the data acquisition phase of your experiment, it is also turned on during conditioning. Conditioning E is always specified vs. Eref, because the open-circuit potential is not measured until after Conditioning is completed.

 

The Conditioning Time is the length of time that the sample is potentiostatted at Conditioning E. The minimum time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

seconds (s), volts (V)

Initial Delay

Use the Initial Delay parameter to tell the system your definition of a stable potential and when to begin the actual measurement. If the absolute value of the Eoc drift-rate falls below the Stability parameter, the Initial Delay phase ends immediately and the experiment begins, disregarding the Time parameter. The drift rate can never fall below zero, so entering a Stability value of zero ensures that the Initial Delay will not end prematurely. A typical value is 0.05 mV/s. The lower limit of the Stability parameter is set by your patience. For example, a stability of 0.01 mV/s indicates a drift of less than 1 mV within 100 seconds.

seconds (s), mV/s

IR Comp

Choose to turn iR-compensation either On or Off. Turning on IR Comp causes the applied potential to be adjusted for the estimated iR-drop.

 

Gamry potentiostats are able to estimate uncompensated voltage-drop caused by cell resistance. They do so by performing a current-interrupt experiment after every data point.