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Cathodic Protection and Corrosion of Nails   

 

What makes nail rust and how Cathodic Protection Works

 

 

This is a little corrosion experiment where we will show how Cathodic Protection works and how is possible to protect a metal, an iron nail in this case, from corrosion using the principle of Galvanic Corrosion.

 

The same principle is used to protect Ship and Offshore structure like Oil&Gas Platform from Corrosion.

 

This experiment shows also how nails rust when are exposed to water.

 

What we will do is to expose two identical iron nails to the same electrolyte, in this case is fresh water with two spoons of NaCl, salt that you use for cooking.

 

One of the nails will be connected through an electrical wire to a piece of aluminium foil, the same used for cooking, while the second nail will be immersed in the same electrolyte.

 

We will leave the two nails for two days immersed in water and then we will see if Cathodic Protection has protected the first nail from corrosion.

 

What we need is:

 

  1. two identical iron nails
  2. a piece of aluminium foil
  3. an electrical wire
  4. something to hang the second nail, we've used an elastic
  5. a glass
  6. two spoons of salt, NaCl, the same that you use for cooking

 

In the pictures below you can see how we've connected the nail to the cable and to the aluminium foil. To fix the aluminum foil just wrap it around the electrical cable and be sure that there is a contact between the aluminum and copper.

 

 

 

cable for cathodic protection of nail

Fig 1 - The electrical wire and elastic

 

 

aluminium foil

 

Fig 2 - Aluminium Foil

 

 

nail connected to aluminium cathodic protection

 

Fig 3 - Nail and Aluminium foil connected to the electrical wire

 

 

what casues rust on nails cathodic protection cell science experiment

 

Fig 4 - Glass with water and salt. You can see how we have immersed the nails. This picture has been taken after two days of exposure. The nail that is not connected to aluminium is corroded.

 

what casues rust on nails all nails

 

Fig 5 - On the left you can see the nail without cathodic protection, in the middle the nail connected to the aluminium foil, cathodically protected, on the right a new nail.

 

rusted nails corrosion

 

Fig 6 -Nails after two days of immersion. You can see how the nail without cathodic protection, that is not connected to the aluminium is severely corroded, see the red rust, while the second nail shown only minor sign of corrosion.

 

 

rusted nail without cathodic protection

 

Fig 7 - Rusted Nail after two days of exposure. You can see the red rust, iron oxide.

In this experiment we've shown how cathodic protection works. When you connect a metal, in this case aluminium, that in the Galvanic series of metals is below Iron, has a lower potential and is anodic, corrodes and protect Iron from Corrosion.

The nail that is not connected to aluminium will corrodes severely after only two days of exposure.

The amount of corrosion is a function of several factors, like the temperature of water, the amount of salt dissolved, the chemical composition of the nail. In this case as you can see in the picture the nails are galvanized, it means that they have a thin superficial layer of zinc deposited on the surface, and this give greater resistance to corrosion compared to steel. If we use a nail that is not galvanized it corrodes faster.

See also:

 

What make nails rust

What causes Rust

Galvanic Corrosion

Cathodic Protection