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Term paper on Aluminum

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Term paper on Aluminum

Post  Tina_0888 on Fri Jan 29, 2010 2:47 am

Aluminum is one of a number of soft metals that scientists call poor metals. It can be shaped and twisted into any form. It can be rolled into thick plates for armored tanks or into thin foil for chewing gum wrappers. It may be drawn into a wire or made into cans. Aluminum is a generally popular metal because it does not rust and it resists wear from weather and chemicals. (Bowman, 391) Aluminum is an element. Its atomic number is thirteen and its atomic weight is usually twenty-seven. Pure aluminum melts at 660.2ºC and boils at 2500ºC. Its density is 2.7 grams per cube centimeter. Aluminum is never found uncombined in nature. (Bowman, 391) Aluminum is a very useful metal that is light, easy to shape and can be strong. This makes aluminum one of the most used metals in the world, right behind iron and steel. (Geary, 185) In its pure state, aluminum is quite weak compared to the other metals. However, its strength can be greatly increased by adding small amounts of alloying elements, heat-treating, or cold working. Only a small percentage of aluminum is used in its pure form. It is made into such items as electrical conductors, jewelry, and decorative trim for alliances and cars. A combination of the three techniques has produced aluminum alloys that, pound for pound, are stronger than structural steel. Some common metals used in alloys for aluminum are copper, magnesium and zinc.(Walker, 31) The added elements give the aluminum strength and other properties. (Newmark, 41) Aluminum is one of the lightest metals. It weighs about 168.5 pounds per cubic foot, about a third as much as steel which weighs 487 pounds per cubic foot. (Neely, 214) As a result, aluminum has replaced steel for many uses. For example, some parts of airplanes, automobiles and trucks are now made of aluminum rather than steel because lighter vehicles use less fuel, making the aluminum alloy container much cheaper to move. (Geary, 185) To make aluminum alloys even lighter, the lightest metal, lithium, is added to aluminum. Products packed in aluminum cost less to ship because the containers weigh less than those made with other metals. The same is true with automobiles the engine block, drive shafts, radiator, wheels and body panels can all be made of aluminum alloys. The car thus weighs less, and, again, the fuel consumption improves. Unfortunately, the price also increases, which is why cars and trucks today are still made of mostly steel. (Advantages to Aluminum) Although pure aluminum is weak, certain aluminum alloys are as strong as steel. Such alloys are used in airplanes, automobiles, guardrails along highways, and in other products that require strength. Aluminum alloys loose some strength at high temperatures. Unlike many other metals, however, they get stronger at extremely low temperatures. Aluminum alloys are widely used in equipment for processing, transporting and storing liquified natural gas, which can have a temperature of -260º F. (Walker, 36) Some metals wear away if exposed to oxygen, water, or various chemicals. When exposed to them a chemical reaction causes most metals to rust or become discolored. When aluminum reacts with oxygen, however, the metal forms an invisible layer of a chemical compound called aluminum oxide. This layer protects aluminum from corrosion by oxygen, water and many chemicals. It makes aluminum especially valuable for use outdoors where the metal is exposed to, and must resist the effects of wind, rain and pollution. (Knapp, 9) Aluminum is a good conductor of electricity. Aluminum and copper are the only common metals suitable for use as electrical conductors. Aluminum conducts electricity two thirds as well as copper; however aluminum weighs a third as much. (Aluminum Facts) Aluminum wire can carry the same amount of electric power as copper wire with a lot less weight. In addition, aluminum can be drawn into wires more easily than copper. Today, more than nine out of every ten miles of large- diameter electrical cable are made from aluminum, rather than traditional copper. This is because aluminum is cheaper and, lighter requiring less pylons to hold up the cables. (Advantages to Aluminum) Like all metals, aluminum conducts heat and can be used either to carry or bring heat to a cold object. Aluminum is sometimes used to make cooling fins, which are sticks of aluminum that bring heat away from an object, such as on a motorcycle, aircraft or a computer chip. Aluminum heats evenly and cools quickly, which also makes it popular for beverage cans and ice cube trays. (Knapp, 14) One of the most useful features of aluminum is its reflective properties. Aluminum reflects about 80 percent of the light that strikes it. (Bowman, 392) This property has made the metal widely used in lighting fixtures. Aluminum also reflects heat as well; it reflects almost nine-tenths of the heat that reaches it. It can be used to reflect heat back inside a room to help keep it warm, or it can be used to reflect heat away from a home to keep it cool. For this reason aluminum is often used as part of the insulation of a house and as roofing material. Also, when fire fighters must walk through flames, they wear special suits coted with aluminum to reflect the strong heat. Astronauts' space suits also have an aluminum coating which prevents extreme heat loss and as well as gain. (Knapp, 21) The food and drink industry is the world's biggest user of aluminum. Factories that make aluminum containers account for about one third of the world's demand for aluminum. (Aluminum Facts) By far the greatest demand is for aluminum cans, which have replaced more traditional tin-plated steel can. A tin can is made from steel that has been coated with tin and sealed by soldering. The tin coating can be scratched away, allowing the steel to rust. Aluminum cans are lighter, do not rust, and can be easily shaped, thus removing the need for soldered seals. In addition, it is easier to paint a decoration or a logo directly on the aluminum, so no more costly paper wrappers are used on steel cans. (Knapp, 23) Aluminum compounds can be used both as a source of carbon dioxide gas and a source of foam. Carbon dioxide gas can, in turn, put out fires. For this reason such combinations were used to make liquid-type fire extinguishers for many years. In the extinguisher the two reagents, the liquids that will react, are kept apart until the extinguisher is to be used. Then a knob on the extinguisher is struck, breaking the seal between the liquids and causing them to react. The reaction produces a gelatinous precipitate of aluminum hydroxide and carbon dioxide gas. The gas cannot easily excape through the sticky liquid, and instead forms bubbles inside it. The result is a foam containing carbon dioxide that immediately squirts from the extinguisher nozzle. (Knapp, 38, 39) This has the effect of blanketing the fire with materials that will not burn, thus preventing oxygen from feeding the flames. The history of aluminum is quite short. The industrial method for separating aluminum from bauxite ore was only discovered in 1854, and the first aluminum was produced in 1859. Now though, it is one of the most important metal industries in the world. The aluminum industry had to wait for the development of electricity before it could exist. In fact the person who first separated aluminum from its ore was Danish professor Hans Christian Oersted, one of the pioneers of electricity. (Bowman, 393) However, only after discoveries in 1886 by Charles Martin Hall of Ohio, Paul L. T. Héroult of France, and in 1888 by Karl Joseph Bayer of Germany, did it become possible to refine large amounts of aluminum. Even then, large-scale processing did not get under way until the early part pf the 20th century. This is because relatively cheap electrical supplies were needed, and it took some time for the power-generating industry to build generators large enough for the needs of an aluminum refinery. Thus aluminum became known in part as the metal of the 20th century, as iron was the metal of the 19th century. Aluminum is essential to many kinds of manufacturing, but making it from bauxite ore requires a great deal of expensive energy. In countries that refine aluminum, one-hundredth of all electricity made by power plants may be used to run the refineries. But once aluminum has been refined and used, it can be melted down and recycled using one-twentieth of the energy it took to make it in the first place. (Bowman, 392) By saving this amount of energy, not only can resources like coal and oil be saved, but less acid rain gases such as sulfur and nitrogen oxides are released in the atmosphere refining and mining for aluminum. For all these reasons it makes sense to recycle. Today, recycling now accounts for about one-half of the total aluminum. Still much energy is wasted mining for aluminum, which could be significantly reduced if more aluminum were recycled. American consumers and industries alone throw away enough aluminum to rebuild the entire U.S. commercial air fleet every three months. (Aluminum Facts) Although it is so widely used, aluminum has only recently come into use. Unlike gold and silver, aluminum is never found uncombined in nature. It is always chemically combined with other elements. People had no way of separating aluminum from these elements until the 1800's. (Walker, 31) A large reason why aluminum is never found uncombined in nature is because it is so strongly attracted to oxygen. (Knapp, 4, 5) Aluminum is a reactive metal. When exposed to the air, it immediately develops an oxide coating that prevents further corrosion. However, along with a few other metals, aluminum compounds can be dissolved by both acids and alkalis. Metal compounds with this special property are called amphoteric metals. This property has been exploited in the aluminum industry as a way of dissolving aluminum compounds from bauxite while leaving the rest of the ore as a solid. This process is called the Bayer process. (Bowman, 392) Bauxite is a red rocklike material. It consists of aluminum oxide and a wide range of unwanted substances. To produce aluminum metal, the ore first has to be concentrated, thus removing the bulk of the impurities. Then it goes to a refinery, where the pure metal is produced. The partly purified ore of bauxite, called alumina, is still a compound of aluminum and oxygen. To refine this aluminum, the alumina has to be dissolved and the aluminum recovered by electrical means. The process of using electricity to separate a metal from its rock ore is called electrolysis and takes place inside electrolysis cells. The alumina has to be liquified so that the aluminum compound will break apart into electrically charged ions. (Bowman, 394) Aluminum ions have a positive charge and can move through a solution to gather at the negatively charged electrode of the cell. Each cell uses a mere four to six volts. However, the current that flows sometimes has as much as 150,000 amps. (Walker, 37) Aluminum is the most reactive metal in common use. All metals more reactive than aluminum (calcium, sodium, etc.) are unstable and need special handling. The reactivity of aluminum has advantages and disadvantages. One advantage is that it reacts with oxygen from the air, forming a gas tight and invisible oxide layer on its surface that protects the metal from environmental corrosion. On the other hand, being so reactive, the metal is very difficult to separate from its ore, and the costs of manufacture are high. (Geary, 185) Aluminum is of great benefit to the world. Hans Christian had no idea what his life changing discovery would contribute when he separated aluminum from its ore. Today an hour cannot pass that you do not see the benefits aluminum brings to our everyday lives. From aluminum cans to electrical wires to computer chips, the tremendous contribution that aluminum has made is beyond calculation. Strong, lightweight, and relatively inexpensive, aluminum improves the quality of the lives of everyone. BIBLIOGRAPHY Advantages to Aluminum. November 28, 2000. Aluminum Facts. November,28 2000. Bowman, Kenneth A. World Book Encyclopedia. Aluminum. Chicago: World Book, Inc., 1992. Cobb, Cathy. Creations of Fire. New York: Plenum Press, 1995 Geary, Don. The Welder's Bible. Pensilvania: Tab Books, 1993. Knapp PhD, Brian. Aluminum. Connecticut: Grolier, 1996. Newmark, Dr. Ann. Chemistry. London: Dorling Kindersley, 1993. Walker, John R. Modern Metalworking. Illinois: The Goodheart-Willcox Company, Inc., 1985.


Advantages to Aluminum. November 28, 2000. Aluminum Facts. November,28 2000. Bowman, Kenneth A. World Book Encyclopedia. Aluminum. Chicago: World Book, Inc., 1992. Cobb, Cathy. Creations of Fire. New York: Plenum Press, 1995 Geary, Don. The Welder's Bible. Pensilvania: Tab Books, 1993. Knapp PhD, Brian. Aluminum. Connecticut: Grolier, 1996. Newmark, Dr. Ann. Chemistry. London: Dorling Kindersley, 1993. Walker, John R. Modern Metalworking. Illinois: The Goodheart-Willcox Company, Inc., 1985.


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