CorroZone Podcast · 16 Jun 2026
Evans Diagrams
- Free
- Lecture
- Beginner
- ~20 min
Mixed potential theory in one picture: how superimposing anodic and cathodic polarisation curves locates E_corr and i_corr, how shifts in cathodic or anodic kinetics move the corrosion point, classifying inhibitors, the diffusion-limited cathode, and predicting galvanic couples and the area-ratio effect.
Show notes
What you'll learn
- Explain how an Evans diagram is constructed by superimposing anodic and cathodic polarisation curves
- Identify E_corr and i_corr graphically from the intersection of the anodic and cathodic curves
- Apply mixed potential theory to justify why the intersection represents the freely corroding state
- Predict qualitatively how changes in cathodic kinetics (e.g., oxygen concentration, pH) shift E_corr and i_corr
- Predict qualitatively how changes in anodic kinetics (e.g., passive film formation, alloying) shift E_corr and i_corr
- Classify corrosion inhibitors as anodic, cathodic, or mixed based on their effect on Evans diagrams
- Describe the effect of a diffusion-limited cathodic curve and explain what controls corrosion rate in the plateau region
- Use Evans diagrams to predict the potential and current in a galvanic couple and explain the area ratio effect
Who this is for
Anyone beginning their study of corrosion — students, engineers, and technical staff who want a solid foundation in why metals corrode and what can be done about it. No prior background assumed.
What you'll learn
- Explain how an Evans diagram is constructed by superimposing anodic and cathodic polarisation curves
- Identify E_corr and i_corr graphically from the intersection of the anodic and cathodic curves
- Apply mixed potential theory to justify why the intersection represents the freely corroding state
- Predict qualitatively how changes in cathodic kinetics (e.g., oxygen concentration, pH) shift E_corr and i_corr
- Predict qualitatively how changes in anodic kinetics (e.g., passive film formation, alloying) shift E_corr and i_corr
- Classify corrosion inhibitors as anodic, cathodic, or mixed based on their effect on Evans diagrams
- Describe the effect of a diffusion-limited cathodic curve and explain what controls corrosion rate in the plateau region
- Use Evans diagrams to predict the potential and current in a galvanic couple and explain the area ratio effect