What causes rusting in Iron and Steel?

Answer 1

Rusting of iron consists of the formation of hydrated oxide, Fe(OH)3, FeO(OH), or even Fe2O3.H2O. It is an electrochemical process which requires the presence of water, oxygen and an electrolyte. In the absence of any one of these rusting does not occur to any significant extent. In air, a relative humidity of over 50% provides the necessary amount of water and at 80% or above corrosion of bare steel is worse.

When a droplet of water containing a little dissolved oxygen falls on an steel pipe, the solid iron or Fe(s) under the droplet oxidizes:

Fe(s) --> Fe2+(aq) + 2e-

The electrons are quickly consumed by hydrogen ions from water (H2O) and dissolved oxygen or O2(aq) at the edge of the droplet to produce water:

4e- + 4H+(aq) + O2(aq) --> 2H2O(l)

More acidic water increases corrosion. If the pH is very low the hydrogen ions will consume the electrons anyway, making hydrogen gas instead of water:

2H+(aq) + 2e- --> H2(g)

But where's the rust? The equations above tell only a small part of the story.

Hydrogen ions are being consumed by the process. As the iron corrodes, the pH in the droplet rises. Hydroxide ions (OH-) appear in water as the hydrogen ion concentration falls. They react with the iron(II) ions to produce insoluble iron(II) hydroxides or green rust:

Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s)

The iron(II) ions also react with hydrogen ions and oxygen to produce iron(III) ions:

4Fe2+(aq) + 4H+(aq) + O2(aq) --> 4Fe3+(aq) + 2H2O(l)

The iron(III) ions react with hydroxide ions to produce hydrated iron(III) oxides (also known as iron(III) hydroxides):

Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s)
The loose porous rust or Fe(OH)3 can slowly transform into a crystallized form written as Fe2O3.H2O the familiar red-brown stuff that is called "rust". Since these processes involve hydrogen ions or hydroxide ions, they will be affected by changes in pH. With limited O2, magnetite is formed (Fe3O4).

If other ions like calcium or carbonate are present, they make a variety of precipitates that mix in with the iron hydroxide to produce a crusty, twisted coating which can either slow corrosion by cutting the iron off from the acid, water, and air supply or grow into convoluted shapes called tubercles. The growth of these tubercles can greatly affect the flow of water through water mains as shown here.

Answer 2

Rust forms when the oxygen in the air corrodes the iron to form iron oxide.

Most metals, when they corrode, the layer of oxide forms a thin layer on the surface of the metal, preventing more oxygen from contacting the metal and preventing further corrosion. Not true with iron. The iron oxide flakes and cracks, exposing more iron and allowing the rust to continue.

Answer 3

Corrosion is an electrochemical process. With steel it is made up of many elements as it is not pure and so if you looked at microscopically the metal has different potentials at different areas. When the metal is surrounded by an electrolyte such as water or soil then an small electro-cell occurs due to the galvanic reaction. In other words current flows from area to another area. The anodic area where current leaves and the other area where the current migrates to is called the cathode. The anodic area is the area where metal ions go into solution and the steel tries to revert back to its original state called ion oxide which is what you see called rust.

There has to present oxygen, moisture, usually chlorides. To protect steel that is surrounded by an electrolyte you can protect against corrosion using Cathodic Protection whereby you place an anode in the ground/water and pass current into them from a DC power source and make the steel you are trying to protect the cathode. The idea is to make the steel more negative by 200mV from its natural state therefore stopping the corrosion process. The anodes corrode but they can be designed for 25-30 years life. If you want to know any more drop me a line as I am a Cathodic Protection Engineer

Answer 4

Rust is the oxidation of iron (Fe).

Oxygen reacts with iron to form Fe2O3.

Preventing oxygen from contacting an iron or steel surface will help slow the material from rusting.

Answer 5

Hi, Rust is a chemical produced when iron compounds corrode in the presence of oxygen and water. It is a mixture of iron oxides and hydroxides.
Rusting is actually a term used for corrosion and usually is corrosion of steel. Iron is the main component of steel.
Thats as much as i know...hope it helps. cheers. RSC

Answer 6

The oxygen in air.
Iron plus oxygen forms iron oxide, which is the rust-brown colour which you see.

Answer 7

iron reacts with oxygen in the air to form a compound called iron oxide. (rust) it can be prevented bystoring the metal with a salt such as calcium chloride, painted or lubricated.

Answer 8

How old are the shafts and are you sure they are steel??? to prevent this you can make sure you keep them dry at all times, especially after your round. If you store your clubs in your trunk of a car, then you should remove them and keep them indoors. The aluminum foil is a good trick actually, but it wont prevent rust, it just takes off most of it. But if they have already started to rust, the integrity of the shaft is compromised and they are weakened dramatically. I would suggest new clubs or shafts before one breaks in your hand.

Answer 9

For a metal to corrode there must be oxygen and water present, as well as an electrolyte. The electrolyte is needed to allow the electrons to move from the metal to the oxygen it bonds with. Possible electrolytes are salt water or a strong acid.

Answer 10

it is caused if no lubricant like oil and grease is applied to iron and steel..yes oxygen causes rusting but not to every iron and steel...just when u diont apply oil and grease