Rusting Of Iron, Corrosion Of Zinc ?

[keysi]

Hi guys, as the title says I just have a couple of questions regarding ^

 

I am aware that rust is a compound that contains water molecules and is an oxidation of iron with oxygen and water, but just wondering if iron can corrode and the result be something else other than rust (no water molecules present - corroded iron, something like that).

And regarding zinc, just that if this is the main difference between the corrosion of iron and zinc, that iron forms rust and zinc would not.

I tried a google search but couldn't find anything specific. Cheers.

[Maine farmer]

When iron rusts, it combines with oxygen to form iron oxide, which does not contain water, unless it is submerged or out in the rain.  Zinc may  be more corrosion resistant, but I think it can oxidize and form zinc oxide, but I am not familiar with details of that process.  I suspect iron is more reactive.  

[exchemist]

There is something of a paradox here. Zinc coatings protect iron and steel because Zn is more prone to oxidation (releases its valence electrons more easily) than Fe. It tarnishes instantly in air but the tarnish coating protects the Zn from further attack. When bonded to iron or steel as in galvanised steel, it is preferentially corroded, releasing its electrons to stop the Fe from being oxidised. It acts as a sacrificial anode (electron source).

 

Eventually the Zn becomes corroded away, though, and at that point the Fe material will start to rust.

 

There are various articles about Zn and galvanising that explain this.

 

Rusting is quite a complicated series of reactions that I don't fully remember. However at the heart of it is O2 + 2 H2O + 4 e- -> 4 OH-, i.e. the formation of hydroxide from oxygen and water, using electrons taken from Fe, which is thereby oxidised to Fe 2+ (and later Fe 3+). 

[jab2]

When iron rusts, it combines with oxygen to form iron oxide, which does not contain water, unless it is submerged or out in the rain.  Zinc may  be more corrosion resistant, but I think it can oxidize and form zinc oxide, but I am not familiar with details of that process.  I suspect iron is more reactive.  

Zinc actually corrode easier than iron.  Galvanizing iron or steel protects it because the corrosion is first confined to the zinc layer as it acts as a sacrificial anode, that is until the zinc has been corroded away. The corrosion product of zinc is Zn(OH)₂.

 

Some reading:

http://www.totalmateria.com/Article40.htm

http://www.totalmateria.com/articles/Art60.htm

http://www.ce.sc.edu/deptinfo/members/faculty/ray/web1/Ugrad/ECIV%20303/Corrosion/Set2%20Chemistry%20of%20corrosion.pdf

 

Oeps, exchemist beat me on the draw.

Edited May 5, 2017 by jab2

[exchemist]

Zinc actually corrode easier than iron.  Galvanizing iron or steel protects it because the corrosion is first confined to the zinc layer as it acts as a sacrificial anode, that is until the zinc has been corroded away. The corrosion product of zinc is Zn(OH)₂.

 

Some reading:

http://www.totalmateria.com/Article40.htm

http://www.totalmateria.com/articles/Art60.htm

http://www.ce.sc.edu/deptinfo/members/faculty/ray/web1/Ugrad/ECIV%20303/Corrosion/Set2%20Chemistry%20of%20corrosion.pdf

 

Oeps, exchemist beat me on the draw.

Yeah, SNAP!!  

 

But at least we are not contradicting one another........... :)

[Maine farmer]

There is something of a paradox here. Zinc coatings protect iron and steel because Zn is more prone to oxidation (releases its valence electrons more easily) than Fe. It tarnishes instantly in air but the tarnish coating protects the Zn from further attack. When bonded to iron or steel as in galvanised steel, it is preferentially corroded, releasing its electrons to stop the Fe from being oxidised. It acts as a sacrificial anode (electron source).

 

Eventually the Zn becomes corroded away, though, and at that point the Fe material will start to rust.

 

There are various articles about Zn and galvanising that explain this.

 

Rusting is quite a complicated series of reactions that I don't fully remember. However at the heart of it is O2 + 2 H2O + 4 e- -> 4 OH-, i.e. the formation of hydroxide from oxygen and water, using electrons taken from Fe, which is thereby oxidised to Fe 2+ (and later Fe 3+). 

I am always learning details here that were overlooked in my education.

[exchemist]

I am always learning details here that were overlooked in my education.

So am I. That is one reason I come here.

 

I had to look up Lagrangian points a couple of days ago, for another thread, which was interesting. :)