After you know the definition corrosion and localized corrostion,you will get the information about mechanism corrosion, just read the article below.
The picture above shows us why the metal to be corroded, just see the reaction process below. This series of steps tells us a lot about the mechanism corrosion.
(1) Ions are involved and need a medium to move in (usually water)
(2) Oxygen is involved and needs to be supplied
(3) The metal has to be willing to give up electrons to start the process
For those step happen the major component of steel, iron (Fe) at the surface of a component undergoes a number of simple changes. Firstly,
<Fe> → <Fen+> + n electrons
The iron atom can lose some electrons and become a positively charged ion. This allows it to bond to other groups of atoms that are negatively charged. We know that wet steel rusts to give a variant of iron oxide so the other half of the reaction must involve water (H2O) and oxygen (O2) something like this
{O2}+ 2 [H2O] + 4e- → 4[OH]
This makes sense as we have a negatively charged material that can combine with the iron and electrons, which are produced in the first reaction are used up.
2<Fe> + [O2]+ 2[H2O] → 2[Fe (OH)2]
Iron + Water with oxygen → Iron Hydroxide dissolved in it.
Oxygen dissolves quite readily in water and because there is usually an excess of it, reacts with the iron hydroxide.
4[Fe(OH)2]+ {O2}→ 2[H2O] + 2<Fe2O3.H2O>
Iron hydroxide + oxygen → water + Hydrated iron oxide (brown rust)
(4) A new material is formed and this may react again or could be protective of the original metal
(5) A series of simple steps are involved and a driving force is needed to achieve them, you can see the schematic process from the picture below.
The most important fact is that interfering with the steps allows the corrosion reaction to be stopped or slowed to a manageable rate in order to get persistence of the right life time of those material.
After you know the mechanism corrosion, so you will be ready to be the corrosion scientist or corrosion engineer, see the next writing how to differ the corrosion scientist and corrosion engineer.
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