Corrosion and Metal Finishing Flashcards

Flashcards defining key terms, chemical mechanisms, and real-world examples of corrosion covered in the lecture notes.

Differential Metal Corrosion

Also known as Galvanic Corrosion or Bimetallic Corrosion, it occurs when two dissimilar metals are brought into contact in the presence of a conductive environment.

Anodic Area in Differential Metal Corrosion

The metal in a galvanic couple that has the lower electrode potential, which undergoes oxidation and corrodes.

Cathodic Area in Differential Metal Corrosion

The metal in a galvanic couple that has the higher electrode potential, which acts as the cathode and remains unaffected by corrosion.

Galvanic Corrosion of Iron and Copper Couple

A bimetallic system where iron ($E^0 = -0.44\,\text{V}$) has a lower electrode potential than copper ($E^0 = +0.34\,\text{V}$), making iron the anode ($\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^-$) which undergoes corrosion, while copper acts as the cathode.

Galvanic Corrosion of Iron and Zinc Couple

A bimetallic system where zinc ($E^0 = -0.76\,\text{V}$) has a lower electrode potential than iron ($E^0 = -0.44\,\text{V}$), causing zinc to act as the anode and undergo corrosion while iron remains protected.

Differential Aeration Corrosion

A form of corrosion that occurs when different regions of a single metal surface are exposed to varying concentrations of oxygen ($\text{O}_2$).

Anodic Area in Differential Aeration Corrosion

The portion of metal exposed to a lower concentration of oxygen ($\text{O}_2$), which develops a lower electrode potential and undergoes corrosion.

Cathodic Area in Differential Aeration Corrosion

The portion of metal exposed to a higher concentration of oxygen ($\text{O}_2$), which develops a higher electrode potential and remains unaffected.

Concentration Cell Mechanism in Aerated Solution

An electrochemical setup where a metal strip in aerated NaCl solution undergoes corrosion at the poorly oxygenated immersed part (anodic: $\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^-$), while the upper aerated region acts as the cathode (cathodic: $\frac{1}{2}\text{O}_2 + \text{H}_2\text{O} + 2e^- \rightarrow 2\text{OH}^-$).

Water Line Corrosion

A type of differential aeration corrosion occurring in liquid storage tanks, where the submerged metal surface below the water line is exposed to less oxygen and corrodes, while the region above the water line remains cathodic and unaffected.

Pitting Corrosion

A localized form of differential aeration corrosion occurring when dust particles or oil droplets deposit on a metal surface, creating a less oxygenated area underneath that acts as an anode and forms a deep, narrow pit.

Examples of Differential Aeration Corrosion

Common everyday occurrences including nails driven into walls, window rods inside frames, partially buried pipelines in soil, paper pins inside paper, and water line corrosion.

Types of Corrosion

The main classifications presented: Differential Metal Corrosion, Differential Aeration Corrosion, and Stress Corrosion.