SPANA

SPANA: Making a Diagram
(run SED or PREDOM)

A diagram may be made using either of the menu “Run / make a Diagram” or “File / Data file / Open (make a diagram)” in the main SPANA window. A new window appears where you can enter all parameters needed to make a diagram with SED/PREDOM:

Data File Name: It is possible to change the input file by clicking this field.

Diagram Name: Enter a name for the plot file.

Diagram:

1. Select first a diagram type from the pull-down menu
2. Change the component(s) in the X- and Y-axis. Change the axes min/max values by clicking on them and entering new values.
3. For redox systems (containing “e−”), choose pe or redox potential (Eh) by clicking on the check-box at the bottom-right of the window. The temperature, selected in DATABASE when creating the input-file, will be used to calculate Eh.
4. Title: If you have selected advanced program level (in the menu Preferences / General options) you may enter a title for the diagram. See how to enter texts in plot files

Concentrations: Change the concentration for each component by clicking on their line in the list-box.

Parameters to make a diagram:
Note that some of the parameters listed below might not appear in the window, depending on the type of diagram selected and program level (normal or advanced in the menu “Preferences / General options”).

• Ionic strength: If “fixed” is selected, and a positive value is given, the calculations will include ionic strength effects. If “calculated” is selected, the ionic strength will be calculated iteratively assuming electroneutrality for the system: sodium or chloride ions will be added to keep each calculation point electrically neutral when calculating the ionic strength of the aqueous solutions.
  The temperature, that was selected in DATABASE when the input-file was created, is used to calculate ionic strength effects. See also activity coefficient models and concentration units in diagrams.
• Number of calculation steps: The number of steps in each axis. Because the programs use a point-by-point plotting technique, increasing this number will increase the resolution of the diagrams. However, this will require longer execution times!
• Output a table with results (SED): output files can be generated by SED with the curve-values in the plots. These are plain text files that will get the same name as the plot file, but with different extension (see menu: Calculation options). You can use these table files to insert the calculated values into a spread-sheet (such as Excel), or you can plot the data with some other plotting program. See also Table Output.
• Show only aqueous species (PREDOM): This will create a predominance area diagram not showing any solid phases that might predominate in parts of the diagram. In this way the underlying aqueous speciation may be visualised.
• Allow reversed concentration ranges: Normally the minimum and maximum concentration limits in the axes are arranged so that minimum values are closer to the origo. If for any rason you need to change that, click on this check box and change the concentration limits. Example of a diagram with reverse concentrations.
• For e−: use Eh check the box to display the redox potential instead of pe as variable in the axes or in the caption. The temperature, selected in DATABASE when creating the input-file, will be used to calculate Eh.