29 Questions
What is overvoltage in a corrosion process?
The difference between the real potential and the equilibrium potential of the cathodic reaction
How does polarization affect corrosion rate?
Decreases corrosion rate
What does Cathodic overvoltage represent in terms of equilibrium potentials?
E - Eoc
What is the significance of 'Me+2 ions' in the context of immersion in a solution?
Helps reach the metal surface
What happens to the anodic overvoltage in a corrosion process?
It is greater than 0
What does 'polarization' refer to in the context of electrodes?
Displacement of electrode potential from its equilibrium value
What does the critic Io value depend on in electrochemical reactions?
Metal-ion concentration
Which operation accelerates corrosion by shortening the path of oxidized ions?
Applying a potential to the metal as anode
What happens to the path of reduced ions when shortening it during an electrochemical operation?
Corrosion is accelerated
Which factor is NOT mentioned as influencing the critic Io value in electrochemical reactions?
Metal composition
What does Me+2 + 2e- represent in the given electrochemical equation?
$Me$ after reduction
How does applying a potential to make the metal behave as anode impact corrosion?
Increases corrosion
What can be drawn to consider the other ions in water for studying metal stability?
Potential-pH equilibrium diagrams
Which region in the Pourbaix diagram indicates the ideal conditions for studying metal?
The region where metal is stable
What do the solid compounds in the Pourbaix diagram represent?
They can either prevent or cause corrosion based on their properties
What does H represent in the corrosion rate formula?
The corrosion rate
What does the value of H less than 0.15 mm/year indicate in the corrosion rate measurement?
Very low corrosion rate
What does the value of H greater than 1.5 mm/year indicate in the corrosion rate measurement?
High corrosion rate
What happens when Me+2 ions reach a suitable surface?
They get electrons and turn into their metal form.
What is the definition of diffusion polarization?
The polarization that occurs when the ion concentration in the solution diverges from the concentration on the electrode surface.
What is the reaction rate controlling step?
The step that needs the most overvoltage among overvoltage types.
What is the definition of total energy amount in the system?
The sum of all the energy types in the system, including overvoltage types.
What happens when Me+2 ions adsorb to the surface and the surface is not suitable for electron exchange?
They spread to other places and turn into their metal form.
What is the definition of overvoltage types?
The types of energy that are higher than the total energy amount in the system.
What is the role of the absorbed hydrogen atoms in activation polarization?
They block the metal's surface from the corrosion process
What happens when a conductive oxide film or adsorbed oxide film or adsorbed gas layer occur on the electrode surface?
The resistance of electrolyte – electrode road increases
What is the relationship between current density and overvoltage in the Tafel equations?
The relationship between current density and overvoltage is exponential
How do Tafel constants change?
They change according to the events that occur at the electrode and the environment
What is T in the system resistance equation?
It represents the sum of activation overvoltage, concentration overvoltage, and IR drop
Study Notes
Corrosion and Electrochemistry
- Equilibrium voltage (Eo) is the potential at which the oxidation and reduction reactions are in equilibrium.
- Overvoltage (η) is the difference between the real potential and the equilibrium potential, η = E - Eo.
Cathodic and Anodic Reactions
- Equilibrium potential for cathodic reaction is Eoc, and for anodic reaction is Eoa.
- Real potential (E) is the potential when the corrosion process takes place.
- Cathodic overvoltage (ηc) is E - Eoc < 0, and anodic overvoltage (ηa) is E - Eoa > 0.
Polarization
- Polarization is the displacement of each electrode potential from its equilibrium value, reducing the potential difference between anode and cathode.
- Polarization values affect the slopes of the curves, and corrosion rate decreases as polarization values increase.
Corrosion Process
- Me+2 ions reach the metal surface and adsorb to the surface.
- Me+2 ions receive electrons and turn into their metal form, Me°.
- Ions can diffuse into metal at the surface and be reduced.
Overvoltage Types
- Total energy amount in the system, ηT = ηD + ηA + ηc + ηcr + ...
- ηD: Diffusion overvoltage, ηA: Adsorption overvoltage, ηc: Charge overvoltage, ηcr: Crystal overvoltage
- The bigger overvoltage type controls the reaction rate.
Polarization Types
- Diffusion polarization occurs when the ion concentration on the electrode surface diverges from the concentration in the solution.
- Activation polarization is the formation of a layer containing absorbed hydrogen atoms that block the metal's surface from the corrosion process.
- Resistance polarization occurs when a conductive oxide film or adsorbed oxide film or adsorbed gas layer occurs on the electrode surface, increasing the resistance of the electrolyte-electrode road.
Measuring Corrosion Rate
- H = G / A.t, where H is the corrosion rate, G is the mass loss, A is the surface area, t is the time, and γ is the density.
- Corrosion rate classification: H < 0.15 mm/year, 0.15 mm/year < H < 1.5 mm/year, H > 1.5 mm/year.
Tafel Equations
- For activation polarization, the relationship between current density (i) and overvoltage (η) is given by the Tafel equations.
- Tafel constants (aa, ac, βa, βc) change according to the events that occur at the electrode and the environment.
Explore the concept of Pourbaix diagrams, which depict the stability of different ions in water and the corrosion behavior of metals. Learn how to interpret the diagrams to identify regions where metals are stable or prone to corrosion. Understand the importance of studying the ideal conditions for corrosion prevention.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
