Corrosion and Degradation Flashcards
6 cards from real ME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Corrosion and Degradation flashcards as text
In electrochemical corrosion, the metal that undergoes oxidation (loses electrons) is called the:
Answer: Anode
At the anode in a corrosion cell, metal atoms are oxidized (M to M2+ + 2e-), causing metal dissolution and material loss.
Galvanic corrosion occurs when two dissimilar metals are in electrical contact in an electrolyte. The more active (less noble) metal will:
Answer: Corrode preferentially as the anode
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.
Passivation in metals like stainless steel involves the formation of:
Answer: A thin, adherent, self-healing chromium oxide film
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.
Pitting corrosion is a particularly dangerous form of localized corrosion because:
Answer: It creates deep, narrow pits that are hard to detect and can initiate stress corrosion cracking
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.
The corrosion protection mechanism of a zinc coating on steel (galvanizing) is primarily:
Answer: Cathodic (sacrificial) protection
Zinc is anodic relative to steel and corrodes sacrificially, providing cathodic protection to the underlying steel even where the coating is scratched or damaged.
Intergranular corrosion in sensitized austenitic stainless steel is caused by:
Answer: Chromium depletion at grain boundaries due to chromium carbide precipitation
When austenitic stainless steel is heated in the sensitization range (450-850 degrees C), chromium carbides precipitate at grain boundaries, depleting adjacent regions below the 10.5% Cr threshold for passivation.