What causes metal to rust?

Rusting is the most common example of metal corrosion, and it happens to materials made up of or containing iron. When the iron comes in contact with air and water, an electrochemical reaction occurs. An oxide forms: iron oxide in its hydrated form.

Yes, it is just the common name for iron oxide. Depending on the type of iron oxide formed, the color may vary from yellow to green. It can also be a mix of these colors. The most common one we see is red rust. It is iron oxide trihydrate or hydrated ferric oxide with a chemical formula of Fe2O3•H2O.

In a nutshell, this is what happens:

iron + oxygen + water → iron oxide trihydrate

This chemical reaction won’t happen without moisture or water. It’s important to safeguard the metal from exposure to moist or wet environments. Water facilitates the transfer of electrons between iron and the environment, which is the oxidation of iron. Let me discuss it briefly below:

  1. When exposed to a strong oxidizing agent such as oxygen, the iron in the metal readily gives up its electrons. It goes into the aqueous solution as a cation.

Fe → Fe2+ + 2e
Balanced equation: 2Fe → 2Fe2+ + 4e

  1. The oxygen and water react with the surface of the metal. The oxygen gets dissolved in the water, forming hydroxide ions.

O2 + 2H2O + 4e→ 4OH

  1. And then, the iron ion and the hydroxide ion react to form iron hydroxide.

2Fe2+ + 4OH → 2Fe(OH)2

  1. Lastly, the iron hydroxide reacts with oxygen to form red rust.

This whole chemical reaction is summarized in the image below. The red brick represents the rust formed.


Image source: Spennemann, D.H.R. from Research Gate

The process is sped up when the metal is exposed to better electrolytes, such as saltwater and acidic solutions/environments. This is because more oxidizing agents are available to attack the iron, corroding the metal faster.

Other metals also undergo this type of corrosion. The resulting oxides cannot be classified as rust simply because they are not iron oxides. For example, silver reacts with sulfur. The oxide called silver sulfide is formed, commonly known as silver tarnish.

How to remove the stains

One of the hassles of rust is when it gets onto clothing or other fabrics. It’s a stubborn stain and will not disappear with the usual laundering tricks. It sticks to the fabric even after using bleach. But here’s the good news: Fabrics can still be saved using lemon juice, salt, and baking soda!

The first thing that I tried was the salt and lemon combo. If the fabric isn’t colorfast, test the lemon juice on it first to check if any bleaching or fading will occur. If there isn’t any, then you can proceed.

  • Put salt on the stained area, and then wet the salted areas with lemon juice. Make sure not to miss any stains!
  • Pick a sunny spot outside, and lay down the fabric. The stained area should be facing the sun. Let the sun do its work.
  • Once the fabric is dry, wash the garment as usual and use a heavy-duty laundry detergent once the fabric is dry.

Try the baking soda and hydrogen peroxide combo next if this technique doesn’t work! This may cause fading, so only on white and colorfast fabrics.

  • In a bowl, add 1-2 spoonfuls. It depends on how much you think you’ll need to cover the stain—of baking soda.
  • Add a few drops of hydrogen peroxide and mix periodically until you get a paste consistency.
  • Apply this paste onto the stained areas, and let it sit for 30-60 minutes. Rinse the fabric with water.
  • Launder the fabric using a heavy-duty detergent.

It’s best to air dry the fabric first if you’re not sure whether you’ve taken out all the stains. The blast of hot air in dryers may set the stain onto the fabric. But if you’re sure that you got all stains out, feel free to use the dryer!

If both home remedies didn’t work, try using a commercially available remover. Make sure that the fabric is colorfast, or else the dye will be washed away. Choose a remover that applies to fabrics. All removers come with their own set of precautions and instructions, so read and follow them carefully.

Almost all removers follow the same procedure: apply it to the stained area, let it sit for a few minutes, Then rinse with water. After that, you can launder the fabric as usual.

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