ME Corrosion and Degradation

Question 1

In electrochemical corrosion, the metal that undergoes oxidation (loses electrons) is called the:

Accepted Answer

Anode

Answer

At the anode in a corrosion cell, metal atoms are oxidized (M to M2+ + 2e-), causing metal dissolution and material loss.

Question 2

Galvanic corrosion occurs when two dissimilar metals are in electrical contact in an electrolyte. The more active (less noble) metal will:

Accepted Answer

Corrode preferentially as the anode

Answer

In a galvanic couple, the less noble metal (more negative EMF) acts as the anode and corrodes faster, while the more noble metal is cathodically protected.

Question 3

Passivation in metals like stainless steel involves the formation of:

Accepted Answer

A thin, adherent, self-healing chromium oxide film

Answer

Stainless steels passivate by forming a thin Cr2O3 film (2-3 nm) that acts as a barrier to further corrosion and spontaneously reforms if damaged in oxidizing environments.

Question 4

Pitting corrosion is a particularly dangerous form of localized corrosion because:

Accepted Answer

It creates deep, narrow pits that are hard to detect and can initiate stress corrosion cracking

Answer

Pitting creates highly localized deep cavities with a large cathode-to-anode area ratio, making it self-sustaining and autocatalytic; the small pit area is easily overlooked visually.

Question 5

The corrosion protection mechanism of a zinc coating on steel (galvanizing) is primarily:

Accepted Answer

Cathodic (sacrificial) protection

Answer

Zinc is anodic relative to steel and corrodes sacrificially, providing cathodic protection to the underlying steel even where the coating is scratched or damaged.

ME - Materials Engineer Practice Test

ME - Materials Engineer Practice Test

ME Corrosion and Degradation