Rusting: Is it Exponential Growth? Best Protection Methods

[Dazz4C]

Sorry if this might be in the wrong section, but I wanted someone's opinion on the formation of rust.

Do you think that the rate of formation of rust on iron/steel is an exponential growth?...


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Also, some extra. I'm doing an EEI on rusting - basically, I'm trying to find the best methods of protection.

In one of my tests, which included a Zinc strip as a sacrificial anode - the iron ended up rusting, even when there was plenty of Zinc remaining. The iron and zinc were touching, so a galvanic cell effect would have been created...I just don't understand why it would have rusted. Also, it was in a sodium chloride solution (Salt Water), so I'm thinking at the moment that the sodium chloride would have had something to do with it.

 

[Borek]

Are you sure there was an electrical contact between iron and zinc? Even if they looked like connected, they could be in reality separated by thin layer of oxides.

I have a feeling you started experimenting without completing the literature research - why sodium chloride speeds up corrosion should be obvious to you after reading about corrosion mechanisms. It lowers water resistance, closing the circuit.

No idea what EEI is. After googling I guess you probably don't mean Edison Electric Institute, East of England International, Energy Economics, Inc. nor Egyptian Educational Initiative. There were more examples even on the first page.

 

[Dazz4C]

Yes, I understand the effect of the sodium chloride; basically it acts as the salt bridge. What I meant was I thought the sodium chloride might have been the cause of the rust in the iron even when the zinc was present. Sorry if it seemed a bit confusing.

Back to the Zinc and the Iron, I didn't think about the thin layer of oxides...I presumed that the zinc oxide would still connect the iron and the zinc strips, creating a electric circuit.

So overall, what you're saying is that the oxides don't close the circuit?

Oh, and EEI stands for Extended Experimental Investigation (In Australian schools)

 

[Borek]

Oxides are usually good insulators.

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[Dazz4C]

Thanks Borek, you've been of great help :)

Now does anyone have any opinions on the spreading of rust?...is it exponential?

 

[Borek]

Unlikely - it may occur only at the surface, and surface is not growing, quite the opposite.

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[Dazz4C]

Sorry - used to maths.

Thanks for all the help though :).