The metals used in so many familiar applications from cooking utensils to skyscraper girders are vulnerable to corrosion. Protective metal coatings can help safeguard these metals so that their structural integrity remains uncompromised.
What Causes Rust?
We usually don’t think of water as an acid, because the pH of pure water is 7, which makes it neither an acid nor a base but a chemically neutral substance. However, the pH of rainwater is typically 5.6, which makes rainwater a weak acid. That means that when rainwater hits iron, negatively-charged hydrogen electrolytes can weaken the bonds that make up an iron atom. This process is known as oxidization. When electrons are shed by the water molecule, hydroxyl ions are formed that have the chemical formula OH. Hydroxyl molecules combine with the weakened iron ion to form hydrous iron oxide (FeOH), which we know better as “rust.”
How Quickly Does Iron Rust?
The environment determines how quickly rust formation takes place. Heat speeds up all types of chemical reactions, so typically iron rusts more quickly in the tropics than it does in more temperate climates. Impurities in water will also affect the rate of rust formation; vinegar and bleach—which are both acids—accelerate rusting.
A thinner piece of iron may seem to rust more quickly than a thicker piece, but that’s just a matter of perception. Holes will appear sooner because there is less density, but actually the two iron objects are rusting at the same rate.
Preventing Rust Formation
Alloys manufactured through the combination of two or more metals often have a greater resistance to corrosion than any of the metals alone. Stainless steel is created by combining iron with carbon and chromium. Other elements such as nickel, molybdenum, silicon or aluminum may also be added to the iron.
Chromium binds with the iron atoms in a way that safeguards them from oxidation. Stainless steel can rust if localized chromium oxide concentrations fall beneath 12 percent. That’s why it’s extremely important to use coatings that will protect stainless steel objects when they’re exposed to potential sources of atmospheric or chemical corrosion.