Excerpt of the Day: How Chromium Helps Stainless Steel Heal Itself

As part of my Excerpt of the Day series, here’s an interesting quote from Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World by Mark Miodownik.

Stuff Matters Book Cover“Normally when steel is exposed to air and water, the iron on the surface reacts to form iron(III) oxide, a red mineral commonly known as rust. When this rust flakes off, it exposes another layer of the steel to further corrosion, which is what makes rusting such a chronic problem for steel structures, hence the need to paint steel bridges and cars. But with chromium present something different happens. Like some hugely polite guest, it reacts with the oxygen before the host iron atoms can do so, creating chromium oxide. Chromium oxide is a transparent, hard mineral that sticks extremely well to steel. In other words, it doesn’t flake off and you don’t know it is there. Instead it creates an invisible, chemically protective layer over the whole surface of the steel. What’s more, we now know that the protective layer is self-healing; when you scratch stainless steel, even though you break the protective barrier, it re-forms.”

For more interesting facts about the science of materials, check out the full book here on Amazon.


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