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
Fretting wear occurs when two surfaces in contact experience:
Answer: Small-amplitude oscillatory motion under load
Fretting is caused by small-amplitude, repetitive relative motion (typically less than 100 micrometers) between contacting surfaces, generating debris and fatigue cracks at the contact interface.
Erosion-corrosion is accelerated corrosion caused by:
Answer: Combined mechanical erosion and chemical corrosion, where flow removes the protective film
Erosion-corrosion occurs when fluid flow or particle impingement mechanically removes the protective corrosion product or passive film, continuously exposing fresh metal to corrosive attack.
Cathodic protection using an impressed current system protects a steel structure by:
Answer: Applying a negative potential to make the steel the cathode, suppressing oxidation
Impressed current cathodic protection (ICCP) forces electrons onto the structure via an external power source, making it cathodic and suppressing metal oxidation (corrosion).
The linear polarization resistance (LPR) technique is used to:
Answer: Rapidly estimate instantaneous corrosion rate without significantly disturbing the corrosion system
LPR applies a small perturbation (plus or minus 10-20 mV) around the corrosion potential and measures the resulting current; the slope (polarization resistance, Rp) is inversely proportional to corrosion rate via the Stern-Geary equation.
Polymer degradation by UV radiation (photo-oxidation) primarily leads to:
Answer: Chain scission and cross-linking, causing embrittlement and discoloration
UV radiation initiates free radical reactions in polymers, causing chain scission (reducing molecular weight) and cross-linking, resulting in embrittlement, chalking, and color change.
Dezincification is a selective corrosion form that occurs in:
Answer: High-zinc brass (greater than 15% Zn) in stagnant or slow-moving water
Dezincification selectively dissolves zinc from brass, leaving a porous, weak copper residue; it is most common in high-zinc brasses exposed to stagnant, slightly acidic, or chloride-containing water.