How does the presence of impurities such as copper affect the rusting of a piece of sheet metal of iron?
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On steel ships, corrosion is greatly increased by having bronze (copper alloy) propellers. Current will flow from the props thru the (salt bridge) seawater, turning the Fe to Fe++. Copper embedded in the steel will do the same. http://www2.ucdsb.on.ca/tiss/stretton/chem2/corrosion.html
The presence of impurities, such as copper, can have different effects on the rusting of a piece of sheet metal made of iron. In the case of copper impurities, it can actually help slow down the rusting process.
To understand how this happens, let's first look at how rusting occurs. Rust, also known as iron oxide, forms on the surface of iron when it comes into contact with oxygen and moisture. In simple terms, it's a chemical reaction between iron, oxygen, and water.
When copper is present in the iron, it forms a protective barrier on the surface of the metal. This barrier, known as a patina, acts as a physical barrier, preventing oxygen and moisture from directly coming into contact with the iron surface. As a result, the rate of rusting is slower compared to pure iron.
To further illustrate this, imagine a piece of sheet metal made of pure iron exposed to oxygen and moisture in the air. The iron will readily react with oxygen and water, leading to the formation of rust over time. On the other hand, if the sheet metal contains copper impurities, these impurities will migrate to the surface and create a protective layer. This layer inhibits the contact between iron, oxygen, and moisture necessary for rusting to occur.
It's important to note that while copper slows down the rusting process, it doesn't completely prevent it. Given enough time and exposure to moisture, rust may still develop on the iron surface, albeit at a slower rate compared to pure iron.
In summary, the presence of copper impurities in sheet metal made of iron acts as a protective barrier, slowing down the rusting process by creating a patina on the metal's surface, which hinders the contact between iron, oxygen, and moisture.