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Molybdenum speciation


Dan A
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Hi,

 

I would like to produce Eh-pH diagrams of Mo speciation including Mo(III) species.

There is one paper by Wang et al 2010 in Corrosion Science which gives thermodynamic data for several Mo(III) species.

My question is if it is possible to implement these data into one of the GWB existing databases?

And if it is possible, how should I do it? (I have never done that before).

 

Thanks,

Dan

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Hi Dan,

 

You can certainly modify the GWB datasets to add new species, minerals, etc. The default dataset distributed with GWB, thermo.dat, does not contain any Mo species, but thermo.com.v8.r6+ does. The Thermo Datasets Appendix to the GWB Reference Manual describes how to add new species to a dataset. If you're going to modify thermo.dat, you'll need to add Mo to the Elements list, add a Mo Basis species, and then one Redox species for each additional valence state that Mo can exist in. You'll then add minerals, aqueous species, or gases written in terms of the original Mo basis species, or one of the redox species.

 

The checklist of information you will need to add can all be found in the appendix. The most important is the logK for the reaction as you've written it. Depending on how the reaction is written in the literature, you may or may not need to adjust its value. If you have deltaGo f values, you'll need to find the deltaGo r, then convert this to a logK for your reaction.

 

I would recommend you take a look at some of the datasets to see what goes into them. Focus on a single element, one that exists in multiple redox states and in multiple phases, perhaps, to see where and how it appears in the dataset. This will make modifying the database more understandable.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

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