Steel is Everywhere
Almost anywhere you look, you will find something made of steel. Cars, trucks, bridges, and skyscrapers get their strength from steel. The same goes for steel cable, pipe, railcars, and guardrails. In addition, the tools used to manufacture these same materials are also made of steel. Henry Bessemer is generally credited with inventing the first technique to mass-produce steel inexpensively (Flavell-While, 2010). His process involved blowing air across molten iron to remove impurities, making it lighter, more malleable, and cheaper to produce (Flavell-While, 2010). As it was known, the Bessemer process was the catalyst for the mass production of steel and paved the road for the bridges, signposts, and cars we see as we travel.
Steel is Not a Real Metal
Although steel is generally considered a metal, it is technically an alloy. Metals occur naturally as an element, for example, iron or aluminum. Steel, an alloy, is a mixture of elements primarily composed of iron and carbon. Most people do not know that as a pure metal, iron is soft. It is made hard by adding elemental carbon to it. Carbon levels varying from .3-2% give it toughness and strength (Oakley, 2014). Levels above that tend to make it too brittle for most industrial uses.
Steel Rusts
Despite being so important, steel has a significant flaw – it rusts. Any unprotected material made with iron and exposed to oxygen and water will corrode. Oxygen makes up almost twenty-one percent of the air we breathe. Water makes up over seventy percent of the Earth’s surface. It’s pretty hard to eliminate steel exposure to oxygen and water, even if we wanted to. The process of rusting can be slow but can destroy even the mightiest bridges and buildings. But what exactly is rust?
Chemistry 101
Rust is the common name for iron oxide and forms when iron goes through the process of oxidation. Simply put, the iron will lose electrons and convert into rust. Rust generally starts by appearing like a light rash on the steel. The rust particle grows and flakes off the base metal during the process. After enough time, oxygen, water, and iron completely convert to rust and disintegrate. Lucky for us, most steel is painted or protected in some way to slow the rusting process down.
Green Corrosion
As a rule, we think of rust or corrosion as being reddish. Depending on its chemical composition, it can be other colors, such as yellow or green (Helmenstine, 2020). Yellow corrosion can be found when there is a very high moisture content, for example, near a body of water. Green corrosion is commonly found on weathered copper, which gets its patina color after being outside and exposed to the weather. In contrast to iron-containing materials, metals such as zinc and aluminum do not rust (although they oxidize). Rather than rusting red, they oxidize white.
If the Earth’s Core is Made of iron, Why Isn’t it Rusting?
The Earth’s core is made up mostly of iron. Why no rust there? The corrosion process occurs when an element that easily loses its electrons (like iron) combines with an element that easily absorbs electrons (oxygen) and then comes into contact with a solution containing an electrolyte (water). Thankful for us there is not a lot of water and oxygen at the center of the Earth. Therefore, rust cannot form.
Conclusion
Modern society could not function without steel. From powerline towers to tanks, it is one of the most important and economical materials ever invented. It is not without flaws. When exposed to two of the most common elements on the face of the Earth, it becomes weak. When you look at it from a chemistry point of view, rust is not that hard to explain. A little iron, mixed with some water, add oxygen, and there it is. Paint it. Protect it. In the end, water and oxygen can be a deadly combination to the life cycle of all things made of steel.
References
Business Insider. (2021). Earth’s core is growing lopsidedly, a new study suggests – and it’s been doing that for at least half a billion years. https://businessinsider.mx/earth-core-lopsided-growing-faster-on-one-side-2021-6/
Flavell-While, C. (2010). Man of steel. TCE: The Chemical Engineer, 833, 68–69.
Helmenstine, A. M. (2020). How rust and corrosion work. ThoughtCo.. https://www.thoughtco.com/how-rust-works-608461#
Oakley, D. (2014). What are the effects of different elements in the chemical composition of steel? Oakley Steel. https://www.oakleysteel.co.uk/chemical-composition-steel
Pexels. (n.d.). Rusty bridge. https://www.pexels.com/photo/photo-of-an-old-rusty-bridge-2530311/