Zinc, a chemical
element, is a shiny, bluish-white metal. It is important in industry. Zinc can be worked
into almost any shape using conventional metalworking methods. Such metals as iron and
steel can be galvanized--that is, coated with zinc--to prevent rusting. Galvanized metal
is used in such products as roof gutters and tank linings. Zinc is also used in electric
batteries. Plants and animals require zinc for normal growth and healing. Zinc is also a
component of the hormone insulin.
Zinc can be combined with other metals to form many alloys (mixtures). For example, brass
is an alloy of copper and zinc. Bronze is copper, tin, and zinc. Nickel silver is copper,
nickel, and zinc. Zinc is also used in solders (easily melted alloys used for joining
metals). Zinc and its alloys are used in die-casting (forming objects from liquid metal in
molds), electroplating (coating an object by using an electric current), and powder
metallurgy (forming objects from metal powder). Since 1982, United States pennies have
been made from a predominantly zinc alloy coated with a thin layer of copper.
Moist air tarnishes (discolors) zinc with a protective coating of zinc oxide. Once a thin
layer of this coating forms, air cannot tarnish the zinc below it. White, powdery zinc
oxide is used in making cosmetics, plastics, rubber, skin ointments, and soaps. It is also
used as a pigment in paints and inks. Zinc sulfide, a compound of zinc and sulfur, glows
when ultraviolet light, X rays, or cathode rays (streams of electrons) shine on it. It is
used on luminous dials for clocks and to coat the inside of television screens and
fluorescent lamps. When mixed with water, zinc chloride, a compound of zinc and chlorine,
protects wood from decay and insects.
Zinc is never found in a pure state in nature. It occurs combined with sulfur in a mineral
called sphalerite or zinc blende. Other zinc-containing minerals are calamine,
franklinite, smithsonite, willemite, and zincite. Zinc is hard and brittle at room
temperature. It is taken from its ores by heating them in air to convert them to zinc
oxide. The oxide is heated with carbon to produce zinc.
Zinc's chemical symbol is Zn. Its atomic number is 30, and its atomic weight is 65.39.
Zinc melts at 419.58 °C and boils at 907 °C. Alloys containing large amounts of zinc
have been found in prehistoric ruins. In the 100's B.C., the Romans made brass coins from
ores containing zinc and copper. The first complete study of zinc was published in 1746 by
Andreas Sigismund Marggraf, a German chemist. |
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