Which process describes the exposure of a metal surface to a conductive, corrosive medium causing the more active metal to become anodic and the less active metal to become cathodic?

Which process describes the exposure of a metal surface to a conductive, corrosive medium causing the more active metal to become anodic and the less active metal to become cathodic?

• A. Direct chemical attack
• B. Uniform etch
• C. Pitting
• D. Electro-chemical attack

Answer: (D)

The process described is electrochemical attack, which is galvanic corrosion. When two different metals are in electrical contact in a conductive corrosive medium, they form a galvanic couple. The more active metal (the one with the lower electrode potential) becomes the anodic region and oxidizes, dissolving into the electrolyte. The less active metal becomes the cathodic region, where reduction occurs and it is protected from further oxidation. The electrolyte provides the path for ions and allows electrons to flow between the metals through the metallic connection, driving this selective corrosion. This differs from a direct chemical attack, which would oxidize without any electrical current or metal-to-metal coupling. It also differs from uniform etch, which would corrode the surface evenly, and from pitting, which is localized rather than a whole-metal anodic/cathodic distribution. The described mechanism—active metal becoming anodic and corroding while the less active metal becomes cathodic—is the hallmark of electrochemical (galvanic) attack.

The process described is electrochemical attack, which is galvanic corrosion. When two different metals are in electrical contact in a conductive corrosive medium, they form a galvanic couple. The more active metal (the one with the lower electrode potential) becomes the anodic region and oxidizes, dissolving into the electrolyte. The less active metal becomes the cathodic region, where reduction occurs and it is protected from further oxidation. The electrolyte provides the path for ions and allows electrons to flow between the metals through the metallic connection, driving this selective corrosion.

This differs from a direct chemical attack, which would oxidize without any electrical current or metal-to-metal coupling. It also differs from uniform etch, which would corrode the surface evenly, and from pitting, which is localized rather than a whole-metal anodic/cathodic distribution. The described mechanism—active metal becoming anodic and corroding while the less active metal becomes cathodic—is the hallmark of electrochemical (galvanic) attack.