Alloys, Smart Alloys and Steel
Alloys- An alloy is a mixture which contains a metal and at least one other element. The added element disturbs the regular arrangement of the metal atoms so that the layers do not slide over each other so easily. Alloys are, therefore, usually stronger and harder than pure metal. Many of the metals we use everyday are alloys. Pure copper, gold and aluminium are too soft for many uses. They are mixed with a small amount of similar metals to make them harder for everyday use.
Smart Alloys- Smart alloys belong to a group of materials that are being developed to meet the demands of modern engineering and manufacturing. These materials respond to changes in their environment, e.g. temperature, moisture, pH and electrical and magnetic fields.
Smart alloys (also called shape memory alloys) remember their shape. They can be deformed, but will return to their shape (usually when they are heated).
Alloys of nickel-titanium, silver-cadmium, copper-aluminium-nickel and copper-zinc-aluminium can possess the shape memory effect. They are useful in thermostats; car, plane and helicopter parts; and flexible frames.
Steel- Carbon is added to iron to make the alloy steel. A majority of iron is convered into steel.
To make steel, the molten iron from the blast furnace is transferred into another furnace. Here it is mixed with recycled scrap metal and pure oxygen is passed into the mixture. The oxygen reacts with the non-metal impurities such as carbon, silicon and sulfur to produce acidic oxides.
Alloys like steel are developed to have to necessary properties for a specific purpose. In steel, the amount of carbon and/or other elements determines its properties:
- steel with a high carbon content is hard and strong, e.g.screwdrivers
- steel with a low carbon content is soft and easily shaped. Mild steel (0.25% carbon) is easily pressed into shape, e.g. cars.
- steel with contains chromium and nickel is called stainless steel. It is hard and resistant to corrosion, e.g.knives and forks.
The Transition Metals and Extracting Transition Me
The Transition Metals- In the centre of the Periodic Table, between groups 2 and 3, is a block of metallic elements called the transition metals. These include: iron, copper, platinum, chromium, titanium, and zinc.
These metals are hard and mechanically strong. They have high melting points (except mercury - which is a liquid at room temperature).
Transition metals, like all other metals, are good conductors of heat and electricity, and can also be easily bent or hammered into shape.
These properties make transition metals very useful as structure materials, and as electrical and thermal conductors.
Extracting Transition Metals-
Copper, aluminium and titanium, unlike iron, cannot be extracted from their ores by reduction with carbon. They are extracted through a process called electrolysis.
Electrolysis is a very complex - there is lots of different stages - requires a large amount of energy. This makes it very expensive. So, we should recycle metals wherever possible to...
- save money and energy
- make sure we don't use up all the natural resources
- reduce the amount of mining because it is damaging the environment.
Copper- Copper is useful for electrical wiring and plumbing but natural supplies of ores containing large quantities of copper are limited. If we continue to use them they will run out completely.
Aluminium- Aluminium is resistant to corrosion. A reaction between the aluminium and oxygen from the air produces a 'thin' skin which prevents further corrosion. It is for this reason that greenhouses don't have to be painted. However, for some uses of aluminium, a thinker layer of this protective oxide is needed.
Aluminium has a low density so it is very light. It is used for...
- drink cans
- window framed
- lightweight vehicles