Melting Point: 1852.0 °C Boiling Point: 4377.0 °C Density: 6.506 g/cm3 State at Room Temp: Solid Color: Grayish-white
Martin Heinrich Klaproth, a leading German chemist in his time, discovered zirconium as part of the compound zircon in 1789. Zircon’s chemical name is zirconium silicate and its formula is ZrSiO4. Zirconium was named from the Persian word “zargun” meaning “gold-like.” This name was not a reference to its chemical properties, but rather to the gold color of the mineral zircon.
Some photos of the gold-colored mineral zircon, ZrSiO4
Although recognized as an element in 1789, zirconium was not isolated until 1824 by a Swedish chemist named Jöns Jacob Berzelius. He isolated the element by heating a mixture of potassium and potassium zirconium fluoride in an iron tube. The reaction produced a black powder that was 93% zirconium.
Zirconium has 28 known isotopes, 5 of which are naturally occurring. 4 of those isotopes are stable, and the other is radioactive. The naturally occurring isotopes and their abundances are listed below: 90Zr: Stable, 51.45% 91Zr: Stable, 11.22% 92Zr: Stable, 17.15% 94Zr: Stable, 17.38% 96Zr: Radioactive, 2.80% (Half-life 3.8 X 1019 years)
Zirconium is most easily found in mineral deposits of zircon (previously mentioned) and in zirconium dioxide, ZrO2 , which is most often associated with lunar rocks. Obtaining pure zirconium is very difficult because it is chemically similar to hafnium, an element of the same group which is always found mixed with deposits of zirconium. Commercial-grade zirconium can contain anywhere from 1 – 3% hafnium.
The Kroll method is used to purify ZrO2 into zirconium. The reactions involved include the following: ZrO2 + 2Cl2 + 2C (900°C) ZrCl4 + 2CO ZrCl4 + 2Mg (1100°C) 2MgCl2 + Zr Air is excluded from these reactions so as to avoid contamination of the product with oxygen or nitrogen.
Zirconium is resistant to corrosion by acids and bases, as well as salt water and various other agents. For that reason, it is used in high performance pumps and valves. Since it does not easily absorb neutrons, zirconium is widely used in nuclear reactors. The zirconium used for this purpose must be nearly free of hafnium, as hafnium can absorb neutrons. Zirconium is also used as an alloying agent in steel, to make surgical equipment, and as a “getter” or a material that combines with and removes trace gases from vacuum tubes.
The majority of zirconium compounds are used to make gems in jewelry. Colorless specimens of zircon (ZrSiO4) are often used as inexpensive replacements for diamonds. These are known as “Matura Diamonds.” Cubic zirconia (a form of is also a popular synthetic gem. It can be colorless, but is easily dyed almost any color. Many inexpensive “birthstone” or engagement rings involve the use of cubic zirconia.
Zirconium dioxide (ZrO2) can withstand very high temperatures and is used to make crucibles and to line the walls of high temperature furnaces Zirconium carbonate (3ZrO2·CO2·H2O) is used in lotions to treat poison ivy. Many different Zirconium compounds are used to make paints, pigments, paper, and adhesives.
Cubic zirconia is judged on a standard of cut and clarity, as are diamonds. At one time, the gems were though to have been “soft diamonds.” When finely divided, the metal may ignite spontaneously in air, especially at elevated temperatures. Zirconium of about 99.6% purity is available at a cost of about $150/kg.