AME 7 Q1

Correct Answers:

A. Using sacrificial anodes made of a more anodic metal to protect the less noble metal from corrosion.
B. Applying coatings or paints to isolate the metals and prevent direct contact.
D. Employing electrical insulation or non-conductive materials between the dissimilar metals to prevent galvanic corrosion.

Explanation:

• A. Using Sacrificial Anodes: This is correct because sacrificial anodes are made of a more anodic metal than the metals being protected. The sacrificial anodes corrode preferentially, protecting the less noble metal from galvanic corrosion.
• B. Applying Coatings or Paints: This is correct because coatings or paints can act as barriers, preventing direct contact between the dissimilar metals and thus reducing the risk of galvanic corrosion.
• D. Employing Electrical Insulation: This is correct because using electrical insulation or non-conductive materials between the dissimilar metals can prevent the formation of a galvanic cell, thereby reducing galvanic corrosion.

C. Increasing the Surface Area of the Less Noble Metal: This is incorrect because increasing the surface area of the less noble metal does not effectively reduce its corrosion rate and may actually increase the rate of corrosion by providing more surface area for the galvanic reaction.

E. Using Metals with Similar Electrochemical Potentials: This is correct in principle but does not directly address the issues of dissimilar metals already in contact. While using metals with similar electrochemical potentials can help prevent galvanic corrosion, the question specifically asks about methods to reduce problems with metals already in contact.

Correct Answers:

A. Galvanic corrosion, where one metal corrodes preferentially due to differences in electrochemical potentials.
C. Formation of an electrolytic cell that accelerates corrosion of the less noble metal.

Explanation:

• A. Galvanic Corrosion: This is correct because when two dissimilar metals are in contact in seawater, they can form a galvanic cell. The metal with a lower electrochemical potential (anodic) corrodes faster than it would if it were not in contact with the other metal, while the metal with a higher electrochemical potential (cathodic) is protected.
• C. Formation of an Electrolytic Cell: This is correct because the contact of dissimilar metals in seawater can create an electrolytic cell that accelerates the corrosion of the less noble (anodic) metal due to the electrochemical reactions.

B. Increased Mechanical Strength Due to Protective Oxide Layers: This is incorrect because dissimilar metals in seawater do not typically result in increased mechanical strength; instead, the primary issue is increased corrosion.

D. Enhanced Durability of Both Metals Due to a Mutual Protective Effect: This is incorrect because dissimilar metals in contact generally lead to increased corrosion rather than enhanced durability. One metal corrodes faster, and there is no mutual protective effect.

E. Decreased Conductivity of Seawater, Which Reduces Corrosion Rates: This is incorrect because the presence of seawater actually facilitates corrosion due to its conductivity and ionic content. Seawater’s conductivity typically accelerates the corrosion process, rather than reducing it.