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Chemistry Corrosion - Concept

Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

Chemistry corrosion occurs as the result of the oxidation of a metal. It is the process of returning metals to their natural state which is ore. Most metals develop a thin oxide coating that protects internal atoms. The protective coating is often applied to protect the metal from oxygen and moisture.

This segment let's go ahead and discuss corrosion which falls under the broader heading of electrochemistry. So whenever you hear the words electrochemistry, you should immediately be tipped off to think about oxidation reduction reactions and in that you should remember where the flow of electrons is coming from. so remember that oxidation is the losing of electrons and reduction is the gaining of electrons and that they happen together in a couple and so you'll have one species that is oxidising and one species that is reducing.

So, in corrosion, basically it involves the oxidation of the metal, which again is something that we're familiar with and so we know that it's the exchange of electrons. So the metal is being oxidised by a reducing agent. So then the proces of returning the metals to their natural state which is the ore, that is what's occurring in corrosion. So it goes from being nice and shiny and pretty to being pretty rusty and disgusting. So obviously, it's not as attrative in its natural ore state as it was in its shiny metallic state.

So since we know that most metals are in reacting in the environment with oxygen, how do we either avoid corrosion or slow it down? So basically most metals develop a thin oxide coating which protects the internal atoms from corrosion. So you might get some initial corrosion on the outside and then at some point they form this oxide film which slows down the process fo corrosion. For instance aluminium is a popular one. Aluminium is very abundantly present in our environment and so it readily loses electrons and so it should be readily oxidised by oxygen. And yet aluminium is used to build lots of large structural things such as airplanes and things of that nature. So it forms a layer of aluminium oxide Al2O3 which inhibits it from further corrosion. And other metals similar, do similar things. Nikel and chromium and actually quite a few others.

So as I stated, a protective coating is often formed by metals on their own or it can actually be applied to protect the metal from oxygen and moisture. You can also use a process called metal alloying. And one of the most common processes that is used in our environment to protect some metals is called cathodic protection and this works for steel tanks and pipes that are burried underneath the ground and so you basically use another metal that furnishes electrons easier than the steel or the iron. In this case we could say magnesium and it's conneceted to a wire and to the pipeline that's to be protected. So basically since magnesium is going to furnish electrons easier than iron, it will be oxidised first and therefore protect the iron. And so basically, it keeps it from being oxidised before a certain amount of time. Obviously at some point teh magnesium will run out and the wires will have to be replaced.

That is corrosion.