The "H" stands for hydrogen, although other standards may be used, and they are for room temperature only. The vertical axis is labeled E H for the voltage potential with respect to the standard hydrogen electrode (SHE) as calculated by the Nernst equation. Pourbaix diagrams are also known as E H-pH diagrams due to the labeling of the two axes. As the Nernst equation is derived entirely from thermodynamics, the Pourbaix diagram can be used to determine which species (metals or alloys) is thermodynamically stable at a given electrode potential (E) and pH. The dashed green lines show the stability limits of water in the system. Pourbaix diagrams are plotted by using the Nernst equation (an equation used to calculate electrode potential). The Pourbaix diagram for uranium in carbonate solution. The diagrams are named after Marcel Pourbaix (1904–1998), the Russian-born Belgian chemist who invented them. Pourbaix diagrams are commonly given at room temperature, atmospheric pressure, and molar concentrations of 10 −6 and changing any of these parameters will yield a different diagram. Beside potential and pH, the equilibrium concentrations are also dependent upon, e.g., temperature, pressure, and concentration. Similarly to phase diagrams, they do not allow for reaction rate or kinetic effects. As such a Pourbaix diagram can be read much like a standard phase diagram with a different set of axes. Boundaries (50 %/50 %) between the predominant chemical species (aqueous ions in solution, or solid phases) are represented by lines. Although passive region has been included in the study, it was unclear from the literature if there was a passive film or how protective it was.In electrochemistry, and more generally in solution chemistry, a Pourbaix diagram, also known as a potential/pH diagram, E H–pH diagram or a pE/pH diagram, is a plot of possible thermodynamically stable phases ( i.e., at chemical equilibrium) of an aqueous electrochemical system. It was found that the stability of carbides is described only by the immune region of the Pourbaix diagram for carbides. It was found that the diagrams are able to explain the results of experimental work performed on chromium carbides in NaOH. Using the thermodynamic data available for the main species at 298 K (25 ☌), Pourbaix diagrams for the chromium carbides are constructed at a concentration of 10−6 M of aqueous species.
The Pourbaix diagrams also known as the E-pH diagrams were constructed for hardfacing alloys based on three chromium carbides: Cr7C3, Cr23C6 and Cr3C2 at 298 K (25 ☌). Marimuthu, Varmaa Dulac, Isabelle Kannoorpatti, Krishnan Significance of Pourbaix Diagrams to Study the Corrosion Behaviour of Hardfacing Alloys Based on Chromium Carbides at 298K (25☌) Significance of Pourbaix Diagrams to Study the Corrosion Behaviour of Hardfacing Alloys Based on.
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