How to draw phase diagram above 300℃？

[Qingping1]

Hello,

     I hope this message finds you well. I'm currently seeking a way to create a phase diagram similar to the attached image. My aim is to gain a deeper insight into the mineral precipitation mechanism. However, I've encountered a limitation with GWB, as it appears to only cover a temperature range of 0-300°C. I'm reaching out to inquire if you might have any suggestions or solutions to overcome this challenge. Your assistance would be greatly appreciated.

Best regards,

Qingping

 

 

 

[Jia Wang]

Hello Qingping,

The limitation here is not with the software. To create a diagram like this, or really to make any type of geochemical calculation, the software draws its thermodynamic information from the dataset loaded. The default dataset, thermo.tdat, has a prescribed range of 0-300C. Also, note that not every reaction within the dataset need to have equilibrium constant data across the full range. The software can create diagrams at any temperature range provided that reactions have information at that temperature range. Does the author of the paper provide the thermodynamic dataset they used? That would be a good starting point.

You can open and view GWB datasets using the TEdit application. To open the thermodynamic dataset loaded in a current GWB app, go to the File menu -> View -> open the dataset.

The GWB apps will also allow you to extrapolate reaction equilibrium constants beyond the prescribed range for the dataset. This option is disabled by default. You can enable it under Config -> Options... In general, I would advise caution when extrapolating log K's for temperature beyond the range of validity prescribed. The further you extrapolate outside the range, the less accurate the values may become.

For more information regarding thermodynamic datasets installed with the software, please see section 2.3 of the GWB Essentials Guide. Information regarding dataset structure, see the GWB Reference Manual. Access the guides from the "Help" menu from any GWB app or the Docs pane on the GWB Dashboard.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[Jia Wang]

Hello Qingping,

Just to follow up with some additional thoughts regarding your question. The pressure command is used for drawing the water stability limits in Act2/Tact, but it does not correct the log Ks defined in the thermo dataset to the pressure of interest. The Log Ks need to be provided specifically at those specific temperature and pressure conditions.

In addition to the information in the paper, the GWB thermo webpage also provides a list of some programs that can be used to generate thermo datasets at arbitrary temperature/pressure conditions.

Hope this helps,
Jia