Is Aluminium a Suitable Metal for Manufacturing Bicycles?

* Al2O3 is left.

Electrolysis

This is how the aluminium and oxygen is separated, through reduction. First the aluminium oxide is added to cryolite (Na3AlF6) to lower its melting point then it is melted at 950'C and placed in an electrolysis cell. The cell is made of steel and is lined with graphite, which is the negative electrode, cathode. At the top of the cell there is the positive electrode, anode, also made of graphite. It is the cathode which reduces the aluminium by giving it electrons.

As the mixture is melted the ions are free to move, which means they can be separated. Oxygen is a negative ion so is attracted to the anode at the top of the cell. Here it loses electrons and becomes a gas. Some of the oxygen reacts with the graphite anode to produce carbon dioxide, this means the anode burns away and must be replaced regularly. The aluminium is a positive ion and so collects at the cathode and gains electrons to form atoms. The cathode is located at the bottom so the aluminium can be tapped off.

At anode:

2O2-(l) - 4e- O2(g)

At cathode:

Al3+(l) + 3e- Al(l)

At Anode:

C + O2(g) CO2(g)

Finance

The abundance of aluminium in the earth's crust compared to other metals is show in the below table:

The table shows that aluminium is the most abundant metal in the earths crust and so there is plenty around for the use in bicycle frames. The bulk

cost of aluminium is £0.082 per 100g, which is the second cheapest in the

The cost of pure aluminium is £1.24 per 100g, which is also the second cheapest in the list.

The below bar chart shows the percentage abundance by mass of each metal more clearly and shows how much more abundant aluminium is than the other metals.

To produce 1 tonne of aluminium takes 2 tonnes of alumina, which in turn takes 4 tonnes of bauxite. To make 1 tonne of aluminium from alumina it takes 14000 to 16000 kilowatt hours of electrical energy. To make 1 tonne of aluminium from recycled aluminium it takes 700 to 800 kilowatt hours of electrical energy.

Environmental Issues

Electrolysis of aluminium requires a lot of electricity and so the pollution caused by the production of electricity is caused by the electrolysis of aluminium. When a fuel is combusted it produces carbon dioxide and any sulphur in the fuel is also oxidised to for sulphur dioxide. Nitrogen in the fuel may be released as the element or, high temperatures, is also oxidised. These gases are all acidic and contribute to acid rain and the greenhouse effect.

Aluminium is a very easy metal to recycle, which is important as it is such a valuable metal. It can be remelted and cast repeatedly without any loss of quality. Also recycling used aluminium needs 95% less energy than producing aluminium from its ore, bauxite. Aluminium is one of the most cost effective materials to recycle because it is so easily and cheaply recycled, but still has a high value on the market.

Production

Aluminium is a very strong metal due to its bonding. Aluminium has a cubic close packed giant structure and its atoms are held together by metallic bonding. The metallic bonding is strong as aluminium forms a 3+ ion.

Aluminium is a light metal as it has a relatively low density, only one third of the weight of steel. Its density is 2.70g/cm3 at 20'C.

It also has an exceptional strength to weight ration. A typical alloy of aluminium has 76% of the strength of carbon steel, but 52% less weight. This means the strength-to-weight ration of aluminium is 46% better than steel. Two metals do have better strength-to-weight ratios than aluminium, they are magnesium and titanium, although the cost of these metals is up to five times that of aluminium.

Aluminium is also resistant to corrosion as a thin and very hard layer of aluminium oxide forms on the surface. This protects the aluminium from chemical and atmospheric corrosion.

Summary

I think aluminium is an ideal alloy to use in the manufacture of bicycle frames for the following reasons:

Advantages

Disadvantages

Most abundant metal in earth's crust.

Expensive to produce from ore.

Easily and cost effectively recycled, using 95% less energy, but still retains quality.

If produced from ore uses a lot of electricity, so contributes to CO2 and SO2 and nitrogen oxide pollution (acid rain).

Cheap bulk cost compared to other metals.

Takes a 4 tonnes of bauxite to produce just 1 tonne of pure aluminium.

Low density and impressive strength-to-weight ratio, so ideal for bicycles as would be light yet strong.

Non corrosive as protected by a thin, strong, transparent layer of aluminium oxide, which protects from moisture, temperature, atmosphere and chemicals.

Aluminium Emma Whiteley

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