Why is zinc used to coat Iron and not the other way around?

Why is Iron not recommended in construction of steam pipes?

Zinc is commonly used to coat iron in a process called galvanization because it provides enhanced protection against corrosion. The reason why zinc is used to coat iron instead of the other way around is mainly due to the difference in their reactivity.

Zinc is more reactive than iron, which means it can act as a sacrificial anode. When zinc and iron come into contact with moisture or other corrosive elements, the zinc will react first and corrode, thus protecting the iron underneath. This sacrificial protection is termed as galvanic protection.

To coat iron with zinc, a process called hot-dip galvanization is typically used. This involves immersing the iron in molten zinc, allowing the zinc to bond with the iron's surface. This coating of zinc provides an effective barrier against rust and corrosion, making it suitable for various applications such as structural steel, pipelines, and outdoor metal structures.

On the other hand, using iron to coat zinc would not provide the same level of corrosion protection. Iron has a lower reactivity than zinc, so it would not sacrificially protect the zinc coating. As a result, the zinc underneath the iron would be vulnerable to corrosion, leading to the degradation of the coating.

Regarding the use of iron in steam pipes, it is generally not recommended due to its limited resistance to high temperatures and the corrosive nature of steam. Iron is prone to oxidation at elevated temperatures, which can lead to the formation of iron oxide (commonly known as rust). In steam pipes, the combination of heat, moisture, and corrosive steam can accelerate the rate of corrosion, leading to pipe deterioration and potential failure.

Instead, materials with higher temperature resistance and better corrosion resistance, such as stainless steel or alloys like Inconel, are commonly used for steam pipes. These materials can withstand the high temperatures and corrosive conditions associated with steam transportation, providing better long-term durability and safety.