Rusting: Is it Exponential Growth? Best Protection Methods

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Discussion Overview

The discussion centers around the formation of rust on iron and steel, specifically questioning whether the rate of rust formation can be characterized as exponential growth. Additionally, participants explore methods of protecting against rust, particularly through the use of zinc as a sacrificial anode in a sodium chloride solution.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • One participant questions whether the rate of rust formation is exponential, suggesting that the surface area of rust may not be increasing in a way that supports exponential growth.
  • Another participant raises the possibility that a thin layer of oxides could prevent electrical contact between iron and zinc, which may explain the rusting despite the presence of zinc.
  • Concerns are expressed about the role of sodium chloride in accelerating corrosion, with one participant suggesting it acts as a salt bridge that could contribute to rust formation.
  • There is a clarification regarding the insulating properties of oxides, indicating that they may not facilitate the electrical circuit necessary for the galvanic protection to work effectively.
  • A participant expresses confusion about the relationship between zinc oxide and the electrical circuit, questioning whether the oxides inhibit the circuit's closure.
  • Another participant acknowledges the effect of sodium chloride on corrosion but emphasizes the need for further literature research to understand its mechanisms.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether rust formation follows an exponential growth pattern, and there are competing views regarding the effectiveness of zinc as a protective measure in the presence of sodium chloride.

Contextual Notes

Participants mention the importance of electrical contact and the role of oxides in the corrosion process, indicating potential limitations in their experimental setups and assumptions about the interactions between materials.

Who May Find This Useful

Individuals interested in corrosion science, materials engineering, or those conducting experiments related to rust prevention and electrochemistry may find this discussion relevant.

Dazz4C
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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.
 
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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.
 
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)
 
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Oxides are usually good insulators.

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

Now does anyone have any opinions on the spreading of rust?...is it exponential?
 
Unlikely - it may occur only at the surface, and surface is not growing, quite the opposite.

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Sorry - used to maths.

Thanks for all the help though :).
 

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