How do I get galvanized steel to rust?

[rick1diana]

I have some galvanized metal roof panels that I want to get rusty very quickly for cosmetic reasons. How do I go about it getting them to get rusty? They are brand new right now.

 

[mrjeffy321]

Galvanized steel has a thin Zinc metal coating to prevent the Iron underneth from oxidizing.
If you want to rust the steel, you will need to remove some/part of the Zinc coating.

Zinc metal is very reactive with acids, especially strong acids. By reacting away some of the Zinc using (for example) Hydrochloric acid, you can expose the Iron below.
Once the Iron is exposed, you could continue using acids to corrode the metal, but this willl not be forming Iron Oxide, rather some other type of Iron salt depending on the acid used. To oxidize the Iron quickly, you might want to use bleach (Sodium Hypochlorite), oxidizing the Iron metal to Fe2O3.
Following this method, you can turn those shinny new roof panels into rusted, old looking, peices of metal fairly quickly...but I don't know how "pretty" it is going to look once your done.

 

[rick1diana]

Thank you so much, I will try that!

 

[3trQN]

Galvanized metals prevent rust not only by protecting the metal from direct oxygen contact, but also by the electrochemistry of zinc. Oxidation can be described as the loss of electrons, when Iron rusts its oxidation state is increased as electrons are transferred away from the metal. Zinc acts as an electron donor in a slighly complex electrochemical reaction like a battery or electrochemical cell, thereby preventing the oxidation of the underlying metal.

Applying electrical currents (not recommended), increasing the temperature and as mrjeffy321 said, removing the galvanised layer can all accelerate rusting.

 

[Gokul43201]

Also, as a result of the chemistry described by 3trQN, you shouldn't expect to remove a small patch of the coating and then be able to oxidize the exposed steel. It won't work too well.

 

[mrjeffy321]

Ideally, you would want to remove as much of the Zinc coating as possible, both to make it easier to oxidize the Iron underneth as well as for the end appearance.
Iron (III) Oxide has that wonderful reddish-brown color whereas Zinc Oxide (both ZnO and ZnO2) is white.

 

[jons_web]

The beauty of galvanized steel compared to painted steel is that it offers galvanic protection. That is, the zinc coating dissolves preferentially to the steel rusting, to protect it despite scratches and cuts in the coating. It is not impossible for an uncoated area to rust, but basically galvanized coatings are ideal for exactly what you are doing. It would do no harm to paint the raw edge of the steel, and if you used a zinc-rich paint (cold galvanizing) that would be best,

view information galvanized steel for http://www.mgexim.com/products.htm

 

[ricaroofers]

You might have to apply some very strong acid on the roof to take off the galvanized coating. And, after that, you might need some iron oxidizer chemicals that can oxidized the metal roof.

 

[nick4u1]

I had to remove the zinc coat off some http://www.cadischmda.com/meshtec.asp I had got because I was working on an art installation and wanted to get an urban look but no one mentioned what acids to use?

 

[MotoH]

Vinegar will remove the galvanized coating. If you plan on welding galvanized, be sure to not breathe the fumes and drink a lot of milk before and after welding. The fumes will screw with you, but the milk will help neutralize them.

 

[nick4u1]

Thats actually quite fascinating...ill guess Ill wear a mask anyway, but the milk didnt come to mind.

 

[chemisttree]

If you don't want vinegar fumes you can use phosphoric acid. It really goes after the zinc but passivates the iron producing a black coating that will rust naturally.