A COMPUTER-PROGRAM FOR CONSTRUCTING STABILITY DIAGRAMS IN AQUEOUS-SOLUTIONS AT ELEVATED-TEMPERATURES

When a metal is placed into an aqueous solution containing various chemicals (oxygen, boric acid, sulfur compounds, chlorides, fluorides, phosphates, etc. ), corrosion problems are often encountered - especially under the high temperature and high pressure conditions present in nuclear power systems. Stability diagrams of metals in aqueous solutions (better known as potential-pH or Pourbaix diagrams) which depict the equilibrium phases of metal, its oxides, its ions, or metal compounds associated with the solution's additives are a valuable means of predicting corrosion. A computer program has been developed for calculating electrode potentials and pHs of reactions and delineating the predominant area of each chemical or ionic species in aqueous solutions. Input is kept to a minimum through an expandable library of species (established as a data base), allowing the retrieval, by name, of thermodynamic and free-energy data. The library contains various compounds of elements Fe, S, Ni, Cr, C, Ni, Ti, B, Zr, and Cu. The free-energy value can be retrieved at any temperature from 25 to 300 C. The stability diagram can be obtained continuously from room temperature up to 300 C and plotted on a digital plotter.