Aluminium Aluminium, the third most common element onEarth after oxygen and silicon, and by far the most abundant metal on Earth, is now used very widely for everything from soft drink cans to car bodies to window frames. Compounds containing aluminium are found in materials as different as antacid medicines, the insulation materials in our homes and in the small white flecks (called vermiculite) in garden composts. Aluminium is one of a number of soft and weak metals (like copper and tin) that scientists call "poor" metals. But aluminium alloys, mixtures of aluminium and other metals, produce materials as tough as steel. The name aluminium comes from the word alumen, which is the Latin name for alum. Alumis an age-old material called a mordant, used for making dyes stick to fabrics. Although it is so widely used today, aluminium has only recently come into use. This is because aluminium is so strongly attracted to oxygen that it can only berefined using huge amounts of electrical energy and electricity did not become readily available until this century. Thus, it is sometimes known as the metal of the 20th century, just as iron was the metal of the 19th century. Although electricity is relatively more plentiful and less expensive than it used to be,refining aluminium from its ore is still a costly process. This is why aluminium is often recycled. This way we do not have to "waste" energy refining more of the metal than we need to. Ruby Ruby is a deep red crystal, one of the most prized of all gemstones. It is made mainly ofaluminium and oxygen (aluminium oxide). This mineral, known as corundum, is transparent. But when it occurs with small amounts of another element, chromium, the colour changes to somewhere between pale rose and deep red. The world's best rubies come from Myanmar (Burma), where they have been naturally weathered from rocks and washed by rivers to accumulate among river gravels. Small rubies can now be made artificially, and these are routinely used in many of the world's lasers. Bauxite Aluminium is found in every handful of soil you hold. It begins as a part of minerals in rocks such as granite. One of the most common minerals containing aluminium is pink or grey feldspar. Tobreak down the feldspar and make clay, all that nature requires is water, warm weather and a very long period of time. As rainwater washes over the surface of the feldspar, invisible chemical reactions occur. They are the same reactions that cause limestone statues on buildings to become weathered. The water, often with carbon dioxide gas from the air, rots the feldspar. The result is to release the elements in the feldspar and put them into solution. The aluminium quickly combines with silicon and oxygen to form clay. Because the clay is formed inwater, it can no longer be destroyed by future rainfall. This is the secret to how aluminium is locked up in the world's clays and why it is so difficult to recover it. The ore containing aluminium, called bauxite, forms in places where the aluminium compounds become especially concentrated. Aluminium refining The partly purified ore of bauxite, called alumina, is still a compound of aluminium and oxygen. To refine this to aluminium, the alumina has to be dissolved and the aluminium recovered by electrical means. The process of using electricity to separate a metal from its rock ore is called electrolysis and takes place inside electrolytic cells. The alumina has to be liquified so that the aluminium compound will dissociate (break apart) into electrically charged particles called ions. Aluminium ions have apositive An aluminium smelter Processing alumina happens on a large scale, but the electrical process cannot be done in a single large vat. Instead hundreds or even thousands of cells are used, made of steel with acarbon lining. The process turns aluminium oxide into aluminium byremoving the oxygen. This is calledreduction. The cells are first filled with a material called cryolite, which is heated to 980°C. Alumina will melt EQUATION: Overall equations for the reduction of alumina to aluminium Alumina Í aluminium + oxygen 2Al2O3(s) Í 4Al(s) + 3O2(g) Carbon + oxygen Í carbon dioxide 3C(s) + 3O2(g) Í 3CO2(g) Other elements are added to create alloys. Alumina (Al2O3) is dissolved in an electrolyte bath of cryolite (Na3AlF6) and aluminium fluoride (AlF3). Crucible Properties of Aluminium A soft, silvery-white metal, chemical symbol is Al Can be toxic to plants if released into the soil by acid rain Melts at a lower temperature than most other metals (660°C) Lightweight metal Extremely strong when combined with other metals Good conductor of electricity Has no taste Easily moulded to other shapes Third most common element, making 8% ofthe Earth's crust Good conductor of heat Atomic number 13, atomic weight about 27