Development of a Software Application for the construction of the Simplified Pourbaix Diagrams Used in the Study of the Corrosion

Abstract

[EN] As a result of the adaptation of the Spanish University to the European Space for Higher Education, changes in teaching-learning methodologies are required. In this context, the development of new software applications can be useful. Pourbaix diagram, also known as a potential-pH diagram, is a graphic representation of the potential with respect to the standard hydrogen electrode (vertical axis) versus the pH (horizontal axis) for a metal under standard thermodynamic conditions (usually water at 25 ºC). The diagram has in account the chemical and electrochemical equilibria and it defines the dominion of stability for the electrolyte (normally water), the metal, and compounds related, for example, oxides, hydroxides, and hydrides. Such diagrams can be constructed from calculations based in the equation of Nernst and in the equilibrium constants of different metallic compounds. Pourbaix diagrams have proved to be very useful in corrosion as well as in many other fields, such as industrial electrolysis, plating, electrowinning and electrorefining of metals, primary and secondary electric cells, water treatment, and hydrometallurgy. Pourbaix diagrams are useful particularly in the study of the behaviour in front of the corrosion of metallic materials, since they permit predicting the zones of immunity, corrosion, and passivation of a metal in an aggressive determined means. If metal in its elementary form is the thermodynamically stable phase, this will indicate conditions of immunity. The corrosion will occur if a soluble cation of the metal is the thermodynamically stable phase. If a soluble complex anion of the cation in alkaline means is the thermodynamically stable phase, which occurs in the case of amphoteric metals, as for example, iron, aluminium, zinc, etc., this will indicate conditions of alkaline corrosion. The passivation will occur if a compound solid of the metal is the thermodynamically stable phase, as for example, oxides, hydroxides or hydrides. This is the reason for which habitually in the studies of corrosion Pourbaix diagrams appear in simplified form showing the described regions and without specifying which the stable species in each condition are. However, manual construction of Pourbaix diagrams is a tedious and systematic task requiring a large amount of time to perform. The development of a software application able to perform Pourbaix diagrams will help to save time in the study of many corrosion problems, as well as problems in other fields cited before. The aim of this work is to develop a new software application for the construction of the simplified Pourbaix diagrams applied to the study of the corrosion. Simplified Pourbaix diagrams with precise delineation of immunity, corrosion, alkaline corrosion, and passivation regions can be an useful tool for the study of the corrosion behaviour of metallic materials both education and research fields.