Basic question about how rust works....

[MM77]

Does bare metal only rust when there's moisture, or does surrounding rust expand even over dry areas (hence the term worm I suppose)??

 

So say there's a section of rust, then the car is stored undercover in a reasonably dry environment, will this rust grow and grow???

[SmokeEm]

Well basically put...

 

Rust- Mechanics

Rust is the common name for a very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen. This open-air oxidization of iron is called rust; it is because of this pure iron is rarely seen in nature. Iron or steel rusting is a common example of corrosion -- an electrochemical process involving an anode, an electrolyte and a cathode. When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the iron of the anode, electrons are freed and the anode becomes rusted. When they flow through the electrolyte and try to combine with any free ions.

 

For iron to rust, three things are needed: iron, water and oxygen. Here's what happens when the three get together:

 

When a drop of water (with dissolved oxygen in it) hits an iron object, two things begin to happen almost immediately. First, the water, a good electrolyte, combines with carbon dioxide in the air to form a weak carbonic acid, an even better electrolyte. As the acid is formed and the iron dissolved, some of the water will begin to break down into its component pieces -- hydrogen and oxygen. The free oxygen and dissolved iron bond into iron oxide, in the process freeing electrons. The electrons liberated from the anode portion of the iron flow to the cathode, which may be a piece of a metal less electrically reactive than iron, or another point on the piece of iron itself.

 

The chemical compounds found in liquids like acid rain, seawater and the salt-loaded spray from snow-belt roads make them better electrolytes than pure water, allowing their presence to speed the process of rusting on iron and other forms of corrosion on other metals.

 

 

Corrosion

Iron and steel are ferrous metals that rust due to the slow oxidation by oxygen and water.

 

Plating with non ferrous metals or painting with a protective film prevent this. Also coating the iron with paint, oil or some other substance to seal it from the elements will prevent rusting

 

You can also use sacrificial metals which are attached to the iron -- a large block of zinc or some other metal that will oxidize more easily than iron. That way all the oxidation happens to the block of this other metal instead of to the iron and you just periodically replace the block.

[Stu_B]

 

You can also use sacrificial metals which are attached to the iron -- a large block of zinc or some other metal that will oxidize more easily than iron. That way all the oxidation happens to the block of this other metal instead of to the iron and you just periodically replace the block.

 

interesting

[mk1mexico]

We use this sacrificial method at work, bolting large blocks of alloys to a huge metal marine structure, essentially sat in sea water all its life. we get sent out to ensure they are 100% bonded to the steel when fitted. Ensuring a good earth bond.

[Vista]

 

You can also use sacrificial metals which are attached to the iron -- a large block of zinc or some other metal that will oxidize more easily than iron. That way all the oxidation happens to the block of this other metal instead of to the iron and you just periodically replace the block.

 

interesting

 

Not much good for cars unless you're planning on turning one into a ship or submarine though as the sacrificial anode needs to be immersed in the electrolyte to provide protection to the steel parts in its vicinity.

[Messenjah]

galvanising is just a sacrificial coating of zinc essentially ... a galvinised chassis will still rust ... once the galv has oxidised away

[sambo]

 

So, now you know!

[mk1estate]

Or to put it simply...get a car take good care of it and you can still watch it rot away...most makers try to protect the cars at the factory by coating them from new, some are better at it than others and some are not ..ie fiat some use better quality steel in the first place and some use a cheaper steel ie fiat.

There will always be some rust eating away at your car ie in box sections but by looking after it and using suitable protection ie waxoil etc you can at least keep it to a minimum, unless you keep it it a dry heated and sealed garage but then whats the point of having a car

[Vista]

galvanising is just a sacrificial coating of zinc essentially ... a galvinised chassis will still rust ... once the galv has oxidised away

 

You're only telling half the story there. Zinc will only oxidise when it comes into contact with air and even then it would be a very very slow process for it to oxidise completely away and leave the steel exposed. So when you take a piece of galvanised steel and then paint it. Providing you don't damage the two coatings you've applied, it'll pretty much last forever.

[MM77]

 

So, now you know!

Yes clearly.

 

Actually to be fair, I think I know less now than when I first posted the question

[SmokeEm]

You asked

[Vista]

Actually to be fair, I think I know less now than when I first posted the question

 

 

http://en.wikipedia.org/wiki/Corrosion

[Toby]

 

The expression "worm" comes from the holes it makes I recon.

 

It's not contageous to fresh, clean metal.

 

Only metal that's expossed to atmosphere.

 

I know a welder who used to make water tanks - he worked on the basis of bare metal being painted within 20mins if possible.

[bigdaz27]

shame they dont make cars out of Titanium as its corrosion-resistant and far stronger then steel

[Fiesta Steve]

I do a bit of sand blasting at work, this gets the steel very clean, if I leave the fresh steel overnight it will have started to rust by morning !!

 

When rusty areas are blasted they appear 100% rust free, but those areas will be VERY rusty next morning.

 

When we buy metal in from the steel merchants it appears to have some kind of coating to help prevent it rusting, not sure what it is?? Sometimes its very greasy too, this annoys me as it means I get my hands dirty

[Toby]

..... kind of coating to help prevent it rusting, not sure what it is?? Sometimes its very greasy too, this annoys me as it means I get my hands dirty

 

It probably oil

[Toby]

Titanium...(is)....far stronger then steel

 

Not true. Pound for Pound yes I think that's true, but things are usually made bigger if they're made of Ti not steel.

[bigdaz27]

Titanium...(is)....far stronger then steel

 

Not true. Pound for Pound yes I think that's true, but things are usually made bigger if they're made of Ti not steel.

 

the russians made submarins out of Titanium becouse its lighter and a lot stronger then steel i was watching somthing on the tv the other day and they got a safe and replaced the door with a thin sheet of steel and one with the same gage of Titanium and put exsplosives in them and the steel one blow staght of the Titanium one just had a big dent in it so i think you will find its a lot stronger

[Toby]

And plastercine is stronger than glass if you're going to hit it with a hammer!

 

 

the russians made submarins out of Titanium becouse its lighter and a lot stronger then steel

 

If you make a con-rod out of steel is has to be much larger in section.

 

Strength comes in all shapes and sizes - like women