Table of Contents
What are Pourbaix diagram explain?
A Pourbaix diagram is a plot of the equilibrium potential of electrochemical reactions against pH. It shows how corrosion mechanisms can be examined as a function of factors such as pH, temperature and the concentrations of reacting species.
What is the Y axis on a Pourbaix diagram?
Pourbaix diagrams depict the most stable species or phase of an element in aqueous solution as a function of potential (on the y-axis) and pH (on the x-axis). Pourbaix’s Atlas of Electrochemical Equilibria in Aqueous Solution contains diagrams for many elements along with extensive notes on their construction.
What are pH diagrams?
A p-h diagram is a figure with a vertical axis of absolute pressure and a horizontal axis of specific enthalpy. It is an important diagram used frequently for a performance calculation of a refrigerating machine. A p-h diagram is made respectively for a specified refrigerant.
How do you draw a Pourbaix diagram?
To plot a Pourbaix diagram the relevant Nernst equations are used. As the Nernst equation is derived entirely from thermodynamics, the Pourbaix diagram can be used to determine which species is thermodynamically stable at a given E and pH. It gives no information about the kinetics of the corrosion process.
What are the dashed lines on a Pourbaix diagram?
The Pourbaix diagram includes the equilibrium potentials of hydrogen and oxygen electrodes as dashed lines.
What are the limitations of Pourbaix diagram?
Limitations of Pourbaix diagrams: The diagrams provide no information about the kinetic parameters of the corrosion reactions. The diagrams consider pure metals and aqueous solutions at standard conditions (temperature 298K, pressure 1 bar, ion concentration 10-6M).
What is the relationship between pH and EH?
pH is commonly said to have a possible range from 1 to 14, but highly acidic solutions can have pH = -1 (10N) and even -2. At 25°C, pH + pOH =14. Eh is a measure of the redox (oxidation-reduction) state of a solution or, more exactly, its solutes.
What is considered as the primary weakness of Pourbaix diagram?
1. These diagrams are purely based on thermodynamic data and do not provide any information on the reactions. The thermodynamic stability may not be achieved to the kinetics of the reaction.
What does a positive Eh value mean?
Higher Eh positive values suggest that reaction is more likely to occur spontaneously without the need of extra energy. The Eh value gives an indication of how likely a given redox reaction will occur.
What is passivity in Pourbaix diagram?
Pourbaix diagrams provide information on three states of metals: Corrosion: active state. Passivity: forming passive layers inhibiting the corrosion process on the surface of the metal. Immunity: thermodynamic stability.