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The whole project consists of four stand-alone experiments. The first one demonstrates the corrosion of a sample of Calcium by measuring the increase of its weight while oxidised by the oxygen of the air. The three other exhibits invite the visitor to experiment with an iron nail, by moving it through different chemical solutions (with a chain and a magnetic holding moved by the handle). The last solution of each experiment is always for rinsing the nail with water or a household cleaning gel in water.
Thus, the visitor observes the three parts of the damaging, repairing and protecting of the nail.
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- Dry corrosion: atmospheric corrosion (oxidation)
The physical change (colour and shape) and the increasing in mass of a sample of calcium interacting with the air at room temperature is shown under the first "dome". A computer connected with a balance compares the evolution of the mass of the calcium. The computer also shows the five last recorded masses and the variation in the last 10 days. This experience introduces the notion of this chemical reaction (oxidation) between the calcium and the oxygen of the air. It also introduces by this experience (as well as the scientific notions of stability, chemical reaction equilibrium, atomic mass, surface reactions, oxidation laws of substances or sample surface calculations.)
- Wet corrosion: etching (iron nail etching)
"Wet corrosion: etching" (2) contains 3 different solutions (the depassivation solution, a copper sulphate solution), the etching solution (an aqueous sodium hypochlorite solution) and the rinsing solution (distilled water). The visitor is guided so that he respects the timing of each step. At the end, the surface of the nail is damaged by the chemical reaction called "oxidoreduction" or "redox reaction".
- Wet corrosion: electrochemical polishing (etched iron nail polishing)
The next wet corrosion exhibit (electrochemical polishing) introduces the idea of what reparation chemistry is able to. The same iron nail damaged by the first wet corrosion box is now plunged in two other solutions. The visitor is guided by a lighted text inside the box. The first vessel contains an electrolyte and electrodes. A bulb prows shows that by introducing the nail in this solution an electric current passes through the liquid. (Then, the nail will be rinsed with water.)
- Wet corrosion: coating (etched, polishing iron nail coating)
Is it possible to protect the iron nail against corrosion? The visitor saw that the phenomenon of corrosion relates to the surface of the object. So, coating the clean nail surface with a substance resistant to corrosion permits to protect it. This is the proposal of the experiment "wet corrosion: coating (etched, polishing iron nail coating)". Here, the timing is very important, too, and the visitor is guided by an explaining display connected to a computer. The first solution is the device of electrolysis containing the coating solution and the electrodes. The etched and cleaned nail will now be coated with zinc, a well-known method. (The second solution(water) is for rinsing the nail).
- Wet corrosion: etching (iron nail etching)
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All four experiments together last about 15 minutes
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With the exception of Gold and Platinum (non-corrosives) the other metals and their alloys react naturally with their close environment. In general, corrosion is the result of a damaging transformation of the metallic material by a gas or a liquid.. It's most known form is rust, which is produced by the contact of iron materials with humid air. But it's also a "memory" in the material life of a metal.
Corrosion is very important as scientific subject spreading in areas of chemistry, physical chemistry, metallurgy...
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The elements are formed by atoms. An atom consists of a nucleus containing positive charges and the negative charges, the electrons, turning around the nucleus. The number of positive charges determinates the element. It is possible that negative charges quit the atom or are added.
When iron rusts, it undergoes an reaction called oxidation-reduction. It's a chemical reaction between two elements constituting in the same time an oxidation and a reduction. An oxidation is the lost of electrons. And a reduction a gain of electrons. The substance gaining the electron(s) is called "oxidant" and the other losing the electron(s) is the "reducer".
