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Explaining Corrosion in 7th-grade Words

(-----) February 26, 2008

My daughter is in the 7th grade as well as many of the authors of these questions. She too is doing a science fair on Corrosion of metal. We typed a paper stating "another way to understand this scientific theory is to think of positively-charged ions sitting in a negatively-charged "gas" of free electrons. The type of gas and its concentration along with the number of electrons present in a metal determine the speed or length of time it will take for metal to corrode". He corrected it with a question mark and put "explain further". He further stated that it was not written for people to understand. I'm not sure how else to explain it so 7th graders can understand. Can you help? Please!

Connie Regennitter
school project - Nampa, Id, USA

February 26, 2008

Sorry, Connie, but I have to agree with the teacher on this one.

Let me give it a go and see what you think --

Corrosion: Metals (except precious metals like gold & platinum) are not found in metallic form in nature because the "oxidized state" -- where the metal has combined with oxygen from the air -- is a more stable state. This is due to the fundamental way that atoms are constructed. Atoms must have the same number of negatively charged electrons as positively charged protons, but that number of electrons may lead to another type of imbalance. Think of how an automobile wheel with a missing lug nut is not properly balanced for smooth rotation. The number of electrons in an atom can result in similar 'holes' in the orbits. Substances like metal and oxygen will react with each other in a way that allows them to transfer or share electrons to fill these electron 'holes'.

Mankind makes the common metals by applying heat to a metal ore while keeping oxygen away from it so as to get it into metallic form. As soon as this is done, nature is back at work trying to get oxygen to combine with the metal and return it to the stable oxidized state. How fast this occurs depends on the metal in question, its surface area ( 0000 steel wool [affil. link to info/product at Rockler] offers far more surface area against which the oxygen can react than a block of steel of similar weight), its temperature (temperature is proportional to movement of atoms, the higher the temperature the more opportunity for reaction), the concentration of the oxygen (the more available oxygen, the more opportunity for reaction), the presence of moisture (moisture allows corrosion currents to flow), and other environmental factors like salt (which makes the moisture more conductive so corrosion can proceed faster).

Good luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

February 29, 2008

Nice answer Ted.

James Watts
- Navarre, Florida

February 29, 2008

Thanks, Jim. If anyone feels they can improve it or make it more understandable for a 7th-grader they are certainly encouraged to take a shot at it.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

March 5, 2008


The teacher wrote for you a question mark in order you could give more references and some figures to illustrate your corrosion idea Model. To endorse your idea
- Write down some bibliographie
- Make a draw of your corrosion idea
- Attach some typical corrosion examples.
Extend your idea for pure corrosion metal and alloys.
Finally, write down a reference where students continue learning more about the subject.

Jose Castellanos
- Minneapolis, MN, USA

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