Aluminum

In spite of the fact that aluminum is very active chemically, it does not corrode in moist air the way iron does. Instead, it quickly forms a thin, hard coating of aluminum oxide. Unlike iron oxide or rust, which flakes off, the aluminum oxide sticks tightly to the metal and protects it from further oxidation. The oxide coating is so thin that it is transparent, so the aluminum retains its silvery metallic appearance. Sea water, however, will corrode aluminum unless it has been given an unusually thick coating of oxide by the anodizing process.

When aluminum is heated to high temperatures in a vacuum, it evaporates and condenses onto any nearby cool surface such as glass or plastic. When evaporated onto glass, it makes a very good mirror, and aluminum has largely replaced silver for that purpose because it does not tarnish and turn black, as silver does when exposed to impure air. Many food-packaging materials and shiny plastic novelties are made of paper or plastic with an evaporated coating of bright aluminum. The "silver" helium balloons that we see at birthday parties are made of a tough plastic called Mylar, covered with a thin, evaporated coating of aluminum metal.

Aluminum conducts electricity about 60% as well as copper, which is still very good among metals. Because it is also light in weight and highly ductile (can be drawn out into thin wires), it is used instead of copper in almost all of the high-voltage electric transmission lines in the United States.

Aluminum is used to make kitchen pots and pans because of its high heat conductivity. It is handy as an air- and water-tight food wrapping because it is very malleable; it can be pressed between steel rollers to make foil (a thin sheet) less than a thousandth of an inch thick. Claims are occasionally made that aluminum is toxic and that aluminum cookware is therefore dangerous, but no clear evidence for this belief has ever been found. Many widely used antacids in the drug store contain thousands of times more aluminum (in the form of aluminum hydroxide) than a person could ever get from eating food cooked in an aluminum pot. Aluminum is the only light element that has no known physiological function in the human body.