Rp/Ec Trend - Setup Parameters

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Rp/Ec Trend - Setup Parameters

Description

 

D - Rp Ec Trend

 

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.

 

Test 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 Identifier string defaults to a name derived from the technique's name. While this makes an acceptable curve label, it does not generate a unique descriptive label for a data set. The Identifier string is limited to 80 characters. It can include almost any normally printable character. Numbers, upper- and lower-case letters, and the most common punctuation characters including spaces are valid.

 

Output File

The name of the file in which the output data are written. By default, it is saved in the default file directory.

 

The input can be a simple file name with no path information. In this case the output file is located in the default file directory. The default file directory is specified in the Gamry.INI file under the [Framework] section with a Key named DataDir. The default path can be changed using the Path command in the Options menu. It can also include path information, such as C:\MY GAMRY DATA\YOURDATA.DTA. In this example, the data are written to the YOURDATA.DTA file in the MY GAMRY DATA directory on drive C. The default value of the Output File parameter is an abbreviation of the technique name with a *.DTA filename extension. We recommend that you use a *.DTA file name extension for your data file names. The data analysis package assumes that all data files have *.DTA extensions.

 

If the script is unable to open the file, an error message box, Unable to Open File, is generated. Common causes for this type of problem include:

•Invalid file name.

•The file is already open under a different Windows® application.

•The disk is full.

 

After you click the OK button in the error box, the script returns to the Setup where you can re-enter the file name.

 

Notes...

Enter several lines of text that describe the experiment. A typical use of Notes is to record the experimental conditions for a data set.

 

Notes defaults to an empty string and is limited to 400 characters. It can include all printable characters including numbers, upper- and lower-case letters, and the most common punctuation including spaces. Tab characters are not allowed in the Notes string. Press the Notes button on the right-hand side to open a separate Notes dialog box.

 

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.

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 100 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 minimum value that we recommend is 0.1 s. The longest Sample Period allowed is 600 s.

 

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. 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 depends on the type of potentiostat you use. Consult your potentiostat manual for more information. A typical Step Size for a polarization resistance scan is between 1 and 5 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 that specified in GLOBALS.exp. If you have more points, the experiment will abort just before the scan phase of the sequence.

seconds (s)

Sample Area

The surface area of the sample that is exposed to the solution. The software uses the sample area to calculate the current density and corrosion rate (if applicable). If you do not want to enter an area, we recommend that you leave it at the default value of 1.00 cm².

 

Gamry tip bulb

Do not enter a value of zero!

cm2

Density

The density of the metal sample, used in calculating the corrosion rate. You may disregard this parameter if absolute corrosion rates are not required for analysis.

g/cm3

Equiv. Wt

Theoretical mass of metal lost from the sample after one Faraday of anodic charge is passed. One Faraday of charge is equivalent to an Avogadro's number of electrons. The Equivalent Weight can be used to calculate the corrosion rate. You may disregard this parameter if absolute corrosion rates are not required.

 

To calculate the equivalent weight for an alloy, you need to know:

•The composition of the metal sample, expressed in mole fractions.

•The atomic weight AW of each alloy constituent.

•The number of electrons n, lost by each component of the sample as it oxidizes.

 

Suppose we have a 40:60 mole-percent Cu:Ni alloy dissolving in an acidic Cl–-solution. Ni forms Ni2+ as it dissolves and Cu forms a Cu+ complex. The equivalent weight is

 

 

 

The above discussion assumes that the sample oxidizes without changing the composition. This is not always the case. The de-zincification of brass is a well-known problem, where under special conditions brass becomes enriched in Cu as it corrodes. If selective dissolution occurs in your system, the best way to find the equivalent weight may be to measure the concentration of your corrosion products in the solution.

g/equivalent

Beta An.

Anodic β (Tafel) coefficient used to calculate the corrosion current Icorr. The value can be adjusted later within the analysis software.

volts/decade

Beta Cat.

Cathodic β (Tafel) coefficient used to calculate the corrosion current Icorr. The value can be adjusted later within the analysis software.

volts/decade

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.

 

Equil. Time

The duration during which the cell remains at the initial potential, with the cell turned on before data acquisition begins. It allows the system to equilibrate before the actual experiment starts. No data are recorded during this step.

 

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The input parameter must be an integer. If equilibration is not required, set this value to 0.

seconds (s)

Repeat Time

The time (specified as hours:minutes) between each test on the cell. For example, if the first test begins at 2:08 and the Repeat Time is 30 minutes, additional tests occur at 2:38, 3:08, 3:38, etc.

minutes (min)

Total Time

The duration of the experimental run. The script keeps track of the elapsed time from the start of the experiment. At the start of each test, the elapsed time is compared to the Total Time. If the elapsed time is greater than or equal to the Total Time, the experiment is halted and the Runner window is closed.

 

The Total Time is always entered in hours. Fractional hours can be entered as decimal numbers. To run a single test, enter a Total Time equal to the Repeat Time or simply run the Polarization Resistance experiment. For N tests, enter a Total Time = N × Repeat Time.

 

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A Total Time of zero results in no tests being run.

hours (hr)

Analysis Region

The region over which the linear fit is performed on the data. It is bounded by x mV positive and negative from the open-circuit potential. For example, if the sample has an open-circuit potential of 0 V and the Analysis Region is 5 mV, the linear fit is performed on data from –5 mV to +5 mV.

mV

Save Raw Data

If enabled, individual Polarization Resistance data files are recorded and saved in addition to the Rp/Ec Trend data file.

 

The file names of the raw data files consist of the main file's name, followed by an underscore and the repeat number in which the data was recorded.

 

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The format of these raw data files is identical to those created by the Polarization Resistance experiments and use the same analysis routines when opened in the Gamry Echem Analyst 2™.

 

 

Related Topics

Multiplexed Rp/Ec Trend