Corrosion

OC46 carry out an experiment to demonstrate that oxygen and water are necessary for rusting

  1. Set up 4/5 test tubes like shown in the diagram.
  2. The 1st & 4th tubes just have water poured in, one is half exposed to the air the other is totally immersed in the water
  3. The 5th tube has no water and therefore is just exposed to air.
  4. The 2nd tube has water that was previously boiled (this has the effect of removing any oxygen in the water). A small amount of oil is poured on top, (this oil prevents any gases from entering the water)
  5. The 3rd tube has Calcium Chloride chips (Irritant) at the bottom of the tube (this has the effect of removing water vapour from the air), the cotton wool will also help remove the moisture from the air.

So what will happen ?

Results

TestTube A TestTube B TestTube C TestTube D TestTube E

Only the nails that were exposed to air and water together rusted,

Conclusion

Air and Water are needed for Iron to rust.

extensions

use deionised/distilled water

use salty water

OC45 understand that rusting is a chemical process that changes iron into a new substance

All metals react with oxygen and oxidise!

Some times this tarnishes the metals. We often use polish to remove this tarnish / oxidisation layer.

Some metals get weaker when they oxidise, this is called corrosion.

In the particular case of Iron, this corrosion is known as Rusting

not a balanced equation due to the fact there are many steps on the road to rust

OC47 methods of rust prevention:

Corrosion in the past and today

One of the first uses of iron was for the production of weapons. Iron weapons had the advantage to be more resistant than the copper ones. But they had the disadvantage to rust very easily. That's the reason why a soldier had to keep his equipment in good shape with a stone and a little bit of oil.

Everyone has already seen a metallic object attacked by corrosion: in a kitchen, in a bathroom or outside: cars, statues...

Today, the massive use of metals made it necessary to find techniques to protect them against corrosion (painting and varnish on the bottom of ships, metallic covering …)

paint,

We paint Radiators, bikes, gates and Lab stools.

oil,

we oil moving parts made from metal

galvanising

Galvanization (or galvanisation) classically refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. Now the term generally refers to an electrodeposition process used to add a thin layer of another metal to an alloy of Iron, in order to prevent rusting.

from wikipedia.org

Sinks are made from Iron, Corregated roofs are made from Iron.... but they have lots of water near them ???? They are coated by a very thin (but complete) layer of Zinc.

galvanizing will inhibit attack of the underlying steel, rusting will be inevitable, especially due to natural acidity of rain. For example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating. Marine and salty environments also lower the lifetime of galvanized iron because the high electrical conductivity of sea water increases the rate of corrosion.

Concerning iron:

Oxidation of iron at high temperatures (about 600 °C):

2 Fe + O2 --> 2 FeO (wustite)

6 FeO + O2 --> 2 Fe3O4 (magnetite)

4 Fe3O4 + O2 --> 6 Fe2O3 (hematite)

Rust is a mixing of oxides and hydroxides of iron. In some cases, it forms a layer which protects the metal in the future by reducing or stopping the progression of the layer of oxide: this effect is called passivation.

Different factors determinate corrosion: the material, the composition in impurities (other elements), the alloys, the forms and quantities of the surfaces, the composition of the air or the liquid and the temperature.

Dry oxidation of calcium

The increasing in mass of a sample of calcium interacting with the air at room temperature:

Dm = f(t)

The increasing of the mass Dm at a time t is:

mt - mi = Dm

(mi is the mass at the beginning mt the mass at the time t)

Oxidation of calcium with dry air:

2 Ca (solid) + O2 (gas) --> 2 CaO (solid)

paint, oil, galvanising