February 21, 2008

Aluminum Definition

Aluminum is the third most abundant element (8%) in the Earth's crust, exceeded by Oxygen (47%) and Silicon (28%). Because of its strong affinity to oxygen, aluminum never occurs as a metal in nature but is found only in the form of its compounds, such as alumina (Al2O3).

 

The metal's name is derived from alumen, the Latin name for alum. In 1807, Sir Humphry Davy assigned the name alumium to the metal and later agreed to change it to aluminum. Shortly thereafter, the name aluminum was adopted to conform with the –ium ending of most elements, and this spelling is now in general use throughout the world, except in the United States and Italy (where alluminio is used).

 

Physical Properties

Aluminum, symbol Al, is a silvery white metal in group IIA of the periodic table. Its atomic number is 13, its atomic weight 26.9815. It is ductile, nonmagnetic, and an excellent conductor of heat and electricity. The density of aluminum at 20 oC is 2.699 g/cm3 (0.1 lb/in2); it melt at 660.24 0C and boils at 2.450 oC.

 

The role aluminum plays in human physiology is not known. Although the metal is ingested through food and water, most of it is believed to be excreted. Aluminum has been detected in the brain cells of ALZEIMER'S patients, but it is not known whether the metal's presence is a cause or an effect of the disease.

 

Lightness and Strength

Perhaps the best-known quality of aluminum is its light weight; it is only about one-third as dense as iron, copper, or zinc. Despite its light weight, it can easily be made strong enough to replace heavier and more costly metals in thousands of applications. Aluminum alloys have the highest strength-to-weight characteristics of any commercial metal.

 

Resistance to Corrosion

Aluminum and its various alloys are highly to corrosion. When exposed to air, the metals develops a thin film of Al2O3, almost immediately. The reaction the slows, however, because the film seals off oxygen, preventing further oxidation or chemical reaction. The film is colorless, tough, and nonflaking. Few chemicals can dissolve it.

 

Electricity and Thermal Conductivity

Aluminum's electrical alloy has the highest conductivity per pound of any commercially sold conductor. Because aluminum is only one-third as dense as copper, it supplies about twice the conductivity per pound. For this reason more than 90 % of the transmission and distribution lines in the United States are made from aluminum. Aluminum is an excellent conductor of heat as well. Because of this it is widely used in automobile radiators; cooling coils and fins, heat exchanger in the chemical, petroleum, and other type of heaters.

 

Reflectivity and Emissive

Aluminum is an excellent reflector of all forms of radiated energy. This characteristic is commonly put to work in building, insulation, including roofing materials. Because it reflects about 90% of radiated heat, aluminum is effective at keeping heat out or in. aluminum foil can also be used to jam radar by reflecting it.

No comments: