A transition metal element, zirconium has an atomic number of 40; the average atomic weight of its isotopes is 91.224. It is found as a bluish amorphous powder or as a grayish-white metal. Zirconium has a melting point of about 3371°F (1855°C) and a boiling point of 7968.2°F (4409°C). Zirconium (atomic symbol: Zr) occurs to the extent of 0.023% in the Earth's crust. It has also been found in moon rocks, the Sun, meteorites, and S-type stars.
Compounds of zirconium had been known for centuries. Zircon, for example, had been used as a gemstone in many cultures since ancient times. However, it was so similar to aluminum oxide that no one had suspected that it contained a new element. Another zirconium-containing mineral was jacinth, also known as hyacinth. This mineral is mentioned in the Book of Revelations as one of the twelve precious stones in the city walls of Jerusalem.
An interesting practice among early chemists and mineralogists was to "adjust" their analyses of compounds so that they always totaled 100%. For example, analysis might reveal that an unknown mineral consisted of 50% silica, 25% alumina, and 15% iron oxide. The remaining 10% was unknown to the analyst. In his or her final report, then, the analyst would adjust those results to show: 56% silica, 28% alumina, and 17% iron oxide in order to make the total add up to 100%.
Martin Klaproth (1743-1817) was probably the first scientist to abandon this practice and actually state when some fraction of the mineral was unknown. As a result, Klaproth was able to discover or verify a number of new elements. Among these was zirconium, which he discovered in 1789. When Klaproth discovered the element, he named it after the mineral (zircon) in which he first found it.
Efforts to isolate pure zirconium from its compounds defeated the best chemists, including Humphry Davy, Jöns Berzelius, and Henri Moissan. Finally, in 1914, D. Lely, Jr. and L. Hamburger produced completely pure zirconium by heating zirconium chloride with metallic sodium.
Zirconium has one special property that accounts for some of its use. It has a very low nuclear cross-section, which means that neutrons to which it is exposed pass through the metal without being absorbed. This property makes it highly desirable as a construction material in nuclear power plants. An additional benefit in this application is that zirconium is also highly resistant to corrosion and damage by heat. One problem, however, is that hafnium usually occurs with zirconium and is very difficult to separate from it. In contrast to zirconium, hafnium has a high nuclear cross-section, which makes it undesirable in nuclear power plant material. The zirconium used in power plants must, therefore, be completely pure of hafnium contamination.
Other uses have been found for zirconium. It is used as an alloying agent in steel, surgical instruments, photoflash bulbs, and lamp filaments. An alloy of zirconium and niobium is superconductive at low temperatures and may be useful in the production of superconducting magnets. Zirconium carbonate is a component of anti-poison ivy lotions. The oxide finds use in pigments, abrasives, enamels, glasses, and furnace linings.