 |
 |
Dear Tamer, for the principles of activity-activity or log(fO2)-pH diagrams you can consult the following paper (with worked examples): Wood, S.A. (1998) Calculation of activity-activity and Log fO2-pH diagrams. Rev. Econ. Geol., 10, 81-96. For simplicity one would prefer to use log(fO2)-pH diagrams instead of Eh-pH diagrams at higher temperatures, Eh-pH diagrams are more commonly used in low-temperature aqueous and environmental geochemistry, mainly because Eh is a directly measurable quantity in water samples (notwithstanding the problems with sensitivity of electrodes to different redox couples, the degee of equilibrium for different redox couples in low-T environments etc.). In terms of software, there is to the best of my knowledge no package that does everything. Geochemists Workbench has a facility for easy construction and plotting of such diagrams, but the thermodynamic datasets that they supply are not well suited for high-temperature environments. A way out is an interface from Yuri Shvarovs HCh/Gibbs program that allows you to export a database better suited for hydrothermal/petrological applications via several steps into a format suitable for input into GWB. This involves purchasing both software packages, which is a bit of investment. Perplex has a facility for constructing and plotting chemical potential diagrams, and Thermocalc appears to have a similar feature. I am not fully up-to-date to what extent those packages have provision for including aqueous species (that you need for considering pH) into such diagrams. Finally you have of course the option to calculate the involved reaction equililibrium constants from some appropriate thermodynamic database, and then construct the diagrams with the help of spreadsheet calculations. This requires also to familiarize yourself with Schreinemakers analysis etc. to find the stable reactions. Best regards, Thomas ------------------------------------------------ Dr. Thomas Wagner Institute for Geochemistry and Petrology ETH Zürich NW F 82.4 Clausiusstrasse 25 CH-8092 Zürich Switzerland phone: ++41-(0)44-6328019 e-mail: [log in to unmask] web: http://www.geopetro.ethz.ch/people/twagner ________________________________________ From: Metamorphic Studies Group [[log in to unmask]] on behalf of tamer Abu Alam [[log in to unmask]] Sent: Tuesday, October 04, 2011 5:24 PM To: [log in to unmask] Subject: PE-PH diagram Dear colleagues If any one know how to draw pE-pH diagram at temperature range (200-700) and pressure around 5 kbar. The mineral assemblage that will be used is ultramfic assemblage (olivine, serp, py,...). If you can recommend me a text book to learn me how to do that. Thank you Tamer