Pourbaix diagram

Pourbaix diagrams (also potential - pH diagram ) illustrate the regions of the thermodynamic stability at the metal -electrolyte systems graphically and are used to predict if a metal can corrode or not.

Description

It is a Cartesian coordinate system is used, wherein the abscissa is the pH, and the ordinate, the normal potential which is determined with the aid of the Nernst equation. Usually, the graphs for a temperature of 25 ° C and a concentration of 1 mol / l are prepared. A distinction is made in three areas: the corrosion area with a concentration of dissolved metal ions > 10-6 mol / l The passivity area with primary formation of oxides and / or hydroxides, which can protect at high adhesion strength against further corrosion. However it can be in a Pourbaix diagram not see how strong the bond strength is pronounced. Therefore, it is challenged by some scientists, the practical utility of these diagrams in question. In the immunity area is the value of dissolved metal ions < 10-6 mol / l

These diagrams were developed in 1938 by Marcel Pourbaix.