Charlie Hunter, age 15, of Barre, Vt., for her question:
WHERE DO WE GET GRAPHITE?
Graphite is one of the softest minerals we have on earth. We find it in nature as a smooth, black, solid that is greasy to the touch. But much of the graphite that is used commercially today is not the natural kind. It is made from coke by heating the coke in electric furnaces.
Graphite is hardened with clay to produce the material in pencils that we call "lead." It was named in 1789 by Abraham Werner, a German geologist. The name comes from the Greek word meaning "to write."
Graphite deposits occur in 25 states of the United States, but only Texas produces natural graphite. The U.S. imports much more natural graphite than it mines. Most comes from the Malagasy Republic, Mexico, Norway and Sri Lanka. The leading natural graphite producers are Australia, China, Mexico, North Korea and South Korea.
After graphite has been mined, it is ground and then purified in settling tanks before marketing. Edward Acheson, an American, developed the process for making graphite from coke in 1898. The U.S. leads the world in the production of manufactured graphite.
Graphite has many uses in addition to its use in pencils. It conducts electricity and does not burn. For these reasons, electrodes or electric contact points made of graphite work under conditions that would destroy metal electrodes.
Graphite conducts heat and does not combine with other chemicals except at very high temperatures. Therefore, many crucibles are made from graphite. A crucible is a melting pot for metals.
Graphite is not easily dissolved and so it is built into tanks which hold strong acid. Also, bricks of graphite form the cores of some nuclear reactors. The graphite slows down neutrons or atomic particles in the reactors to keep the reactors operating properly.
Graphite's slipperiness makes it a good lubricant for clocks, door locks and other machines with small parts.
Graphite is also the only major raw material that is used in making man made diamonds. Although it is extremely soft, graphite is the same chemical element as diamond, which is the hardest natural material. Both graphite and the diamond are made of pure carbon.
A piece of graphite contains many very thin, flat crystals or groups of atoms arranged in a regular pattern. The carbon atoms in each group cling tightly to each other. But the groups themselves slip easily on other groups. This sliding accounts for graphite's softness and greasy feel.
Graphite was mistaken for lead metal at one time and even today it is sometimes called "black lead."
Graphite will not fuse with metals by heat alone. But it can be powdered and mixed with powdered metals, pressed into shape and heated to make a bearing. Such a bearing does not need frequent oiling because the graphite acts as a self lubricant.