Question

If you were going to apply a small potential to a steel ship resting in the water as a means of inhibiting corrosion, would you apply a negative or a positive charge? Explain.

Short answer

To inhibit corrosion in a steel ship resting in the water, a negative charge should be applied. This is because the negative potential will counteract the natural corrosion process on the steel surface by suppressing the oxidation of the steel and promoting the reduction of dissolved oxygen in the water. As a result, the rate of ferrous ions release will decrease, reducing the overall corrosion rate of the steel.

Step-by-step solution

Understand corrosion

Corrosion is an electrochemical process that occurs when a metal reacts with its environment, such as water, to form an oxide, hydroxide, or other compounds. In the case of steel, the primary component that corrodes is iron, which reacts with oxygen and water to form rust (iron oxide). The corrosion process involves the transfer of electrons, making it sensitive to the applied electric potential.

Cathodic protection

One method to inhibit corrosion is called cathodic protection. This technique involves applying an electric potential to the metal, which influences the electrochemical reactions occurring on the surface of the metal and reduces the rate of corrosion. There are two types of cathodic protection: galvanic (sacrificial) and impressed current. In galvanic cathodic protection, a more active (anodic) metal is connected to the metal that needs protection, while in impressed current cathodic protection, an external power source is used to provide the required potential. In both cases, the purpose is to create a flow of electrons from the anode (oxidizing site) to the cathode (reducing site), thus suppressing the corrosion reactions.

Determine the required electric potential

To inhibit corrosion in the steel ship, we need to apply an electric potential that would counteract the corrosion process occurring naturally on the steel surface. The aim is to suppress the oxidation of the steel (ferrous ions release and electron loss) and promote the reduction of oxygen in the water. To achieve this, we should apply a negative charge to the steel ship. By doing so, the electrons supplied by the negative potential will reduce the corrosion process as the metal surface will become a cathode, and the rate of ferrous ions release will decrease.

Explain the conclusion

Applying a negative charge to the steel ship will inhibit corrosion by making the ship's surface more negatively charged. This negative potential will restrict the oxidation process (release of ferrous ions and electron loss) and promote the reduction of dissolved oxygen in the surrounding water. As a result, the corrosion rate of the steel will be reduced. Therefore, to prevent the steel ship from corroding, a negative charge should be applied.