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Sun 7 Nov, 2004 09:51 am
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I have a question about corrosion. I just did a science lab to determine if salt water would make a piece of steel rust faster than plain water. I put 7.5mL of salt, 15mL and no salt and observed them for 6 days. It turned out that all the pieces rusted at the same rate but the rust on the no salt was bright orange while the rust on the slat water pieces was a dull brown. I would have expected the salt to make it rust faster but that is not what I observed.
Q: Why is the rust on the salt water pieces brown while the rust on the just salt is bright orange?
Q: Why did the salt not make it rust faster?
Essentially your experiment is the same as if you tried to find out if people age faster while on fire. You can't simply look at the skin afterwards to find out. Hope that helps.
Rust Colors
What we call rust is actually a family of Iron Oxides. Different combinations of Fe and O produce different products. In many industrial applications, iron is "pre-rusted" in conditions to produce the "right kind" of corrosion. That iron oxide layer then protects the metal against other kinds of corrosion.
What I suspect is that your salt water solution favored the formation of one type of oxide over another. Try
http://www.corrosion-doctors.org/Experiments/iron-products.htm for more info.
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