Rust is a result of corrosion where iron reacts with oxygen and water, forming porous iron hydroxides. Rust can be superficial or deep, and the latter can weaken the material's strength quickly. In a demonstration, citric acid is used to remove rust from affected tools. After cleaning with soap and a protective treatment with cooking oil, future rust formation is prevented.
Last edited on May 8, 2024
First, let's clarify the concepts!
What is rust?
Rust is "flaky," porous iron hydroxides that contain water. Most often, rust is reddish-brown. Rust is formed when iron corrodes, another word for rusts. For something to rust, water and oxygen are needed. Because rust is porous, it does not protect the underlying iron from further corrosion but instead causes it to rust even faster once it has started to rust.
Rust forms in two stages. First, there is red rust, which is light reddish-brown and less serious. This rust can often be removed. We'll show you how! But if the red rust is left, it eventually becomes heavy rust, which is dark brown or black. Heavy rust is hygroscopic, which means that it absorbs moisture, and in the presence of moisture, the attack goes deep. The strength of the affected object deteriorates rapidly.
We will now see if we can remove ALL rust from these pliers?
The pliers are affected by both superficial rust and deep heavy rust. One might now think that we would need something very strong, but with a little simple chemistry, that is not necessary at all. We need an acid – and ordinary citric acid is enough.
Citric acid is added as an antioxidant in, for example, juice and jam and is found in the list of ingredients as E330; citric acid is also used to preserve vitamins in food. The chemical designation is C6 H8 O7. Citric acid is therefore acidic but not dangerous; citric acid occurs naturally in lemons, as the name suggests.
Here we have placed the pliers and the small bell in a bath with water and 4 tablespoons of citric acid. As you can see in the picture below, the superficial rust disappears immediately, but since these objects are severely affected, they remain in their bath.
Below you can see the bath after two days.
The loose rust lies at the bottom of the bowl.
The objects are now free of rust, and we clean them with soap and eco-fiber cloth to remove the citric acid and the last of the rust that is now loose.
Here you can see how deeply affected the pliers have been by rust in some places.
To protect the objects from future rust attacks, we put them in cooking oil and heat them up in a frying pan for a short while but at high heat. When they have cooled, we wipe them clean with paper or a cloth.
Bluing is a method for rust protection. What you do is heat the metal in question (often iron) to about 300°C and then apply linseed oil. This protects against rust and the iron gets a deep, black surface, which is why it is called "bluing." Here, instead of linseed oil, we have used ordinary cooking oil (rapeseed).
Before
After
__________________________________________________________________________
Questions and Answers
- Why are water and oxygen needed for iron to rust?
Rust formation requires both water and oxygen.
Water enables the corrosion reaction by acting as an electrical conductor, while oxygen is part of the chemical process.
- How can you remove superficial rust from an object?
Superficial rust can be removed by using an
acid, as in this case citric acid. The citric acid reacts with the rust and dissolves it from the surface.
- What is hygroscopic rust and why is it dangerous?
Hygroscopic rust, such as heavy rust, is dark
brown or black and has the ability to absorb moisture from the environment. This causes the rust to continue to attack
the object deeper and faster, which impairs its strength.
- How do you protect objects from future rust attacks after cleaning them?
After cleaning, the
objects are treated with cooking oil and heated in a frying pan to form protection against rust. This creates a barrier
between the metal and moisture, which prevents corrosion.
- What is bluing and how is it performed?
Bluing is a method for rust protection where the metal is
heated to about 300°C and then treated with linseed oil to give a deep black surface. In this case, ordinary cooking oil
was used instead of linseed oil to achieve similar protection.