Phase diagrams
Phase diagrams are useful tools for the design of processes. A phase diagram shows the conditions at which different phases are in thermodynamic equilibrium. Phase diagrams are visual tools to display the properties of pure compounds forming various phases at different temperatures and pressures.
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Extended UNIQUAC model
The model has proven itself applicable for calculations of vapor-liquid-liquid-solid equilibria and of thermal properties in aqueous solutions containing electrolytes and non-electrolytes. The extended UNIQUAC model consists of three terms: a combinatorial or entropic term, a residual or enthalpic term and an electrostatic term.
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Free sample program
Equilibrium calculations based on the Extended UNIQUAC model can be performed with Microsoft Excel® as user interface. A digitally signed sample program can be downloaded for free.The program includes the ions Na+, H+, Cl-, HSO4-, SO42-, and OH-.
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Calculation of salt precipitation and phase diagrams

The phase diagrams shown on these pages are calculated with the Extended UNIQUAC thermodynamic model. Calculation of phase diagrams and salt precipitation can be done in easy to use software. The software is programmed as FORTRAN DLL and has Microsoft Excel as user interface.

A demo version can be downloaded below.


On this page, phase diagrams for the following systems are being shown:

  • Iron bromide-water
  • Aluminum fluoride-water
  • Ammonia-phosphoric acid-water
  • Sodium chloride – potassium sulfate – water
  • Iso-propanol – potassium sulfate – water
  • Aluminum chloride – hydrochloric acid – water
  • Magnesium hydroxide – phosphoric acid – water
  • Calcium sulphate – water
  • barium sulfate – water
  • Ammonia – carbon dioxide – water
  • Sodium hydroxide – phosphoric acid – water
  • Calcium chloride – potassium chloride – sodium chloride – water
  • Lithium hydroxide – boric acid – water
  • Aluminum chloride – potassium chloride – hydrochloric acid – water
  • Aluminum sulfate – sodium sulfate – water
  • Calcium carbonate – carbon dioxide – water
  • Calcium hydroxide – water

Understanding the thermodynamics of aqueous salt solutions

Activity coefficients, osmotic coefficients, calculation of salt precipitation, super-saturation,  phase diagrams, and other aspects of electrolyte solution thermodynamics are described in a compendium by Kaj Thomsen, “Electrolyte Solutions: Thermodynamics, Crystallization, Separation methods”. The compendium can be downloaded at no cost at Ph.D. thesis by Kaj Thomsen: “Aqueous Electrolytes Model Parameters and Process Simulation” can be downloaded at
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