n. (Symbol Zr)

A lustrous, grayish-white, strong, ductile metallic element obtained primarily from zircon and used chiefly in ceramic and refractory compounds, as an alloying agent, and in nuclear reactors as a highly corrosion-resistant alloy. Atomic number 40; atomic weight 91.22; melting point 1,852°C; boiling point 4,377°C; specific gravity 6.56 (20°C); valence 2, 3, 4.

Background

Zirconium, symbol Zr on the Periodic Table, is a metal most often found in and extracted from the silicate mineral zirconium silicate and the oxide mineral baddeleyite. In its various compound forms, the grayish-white zirconium is the nineteenth most plentiful element in the earth's crust, where it is far more abundant than copper and lead. It belongs to the titanium family of metals, a group that also includes titanium and hafnium and that is favored in industry for its members' good electrical conductivity as well as their tendency to form metallic salts. Because it is stable in many electron configurations and physical states, zirconium can be made into many products. However, since the 1940s, its most significant applications have been in various structural components of nuclear reactors.

Zirconium was discovered by German chemist Martin Heinrich Klaproth, who first isolated an oxide of the mineral zircon in 1789. The first metallic powder was produced in 1824 by a Swedish Chemist, Jons J. Berzelius. The forms of the metal that could be isolated during the nineteenth century, however, were impure and thus very brittle. The earliest method of purifying useable quantities of the metal was developed in 1925 by Dutch chemists Anton E. van Arkel and J. H. de Boer, who invented a thermal iodide process by which they thermally decomposed zirconium tetraiodide. The drawback with van Arkel and de Boer's method was its cost, but twenty years later William Justin Kroll of Luxembourg invented a cheaper process, using magnesium to break down zirconium tetrachloride. Relatively inexpensive, this process produced zirconium in quantities large and pure enough for industrial use.

Since Kroll's breakthrough, zirconium has become an important element in several industries: steel, iron, and nuclear power. It is used in the steel industry to remove nitrogen and sulfur from iron, thereby enhancing the metallurgical quality of the steel. When added to iron to create an alloy, zirconium improves iron's machinability, toughness, and ductility. Other common industrial applications of zirconium include the manufacture of photoflash bulbs and surgical equipment, and the tanning of leather.

Despite its ability to be used for many different industrial applications, most of the zirconium produced today is used in water-cooled nuclear reactors. Zirconium has strong corrosion-resistance properties as well as the ability to confine fission fragments and neutrons so that thermal or slow neutrons are not absorbed and wasted, thus improving the efficiency of the nuclear reactor. In fact, about 90 percent of the zirconium produced in 1989 was used in nuclear reactors, either in fuel containers or nuclear product casings.

Raw Materials

Of the two mineral forms in which zirconium occurs, zircon is by far the more important source. Found mainly in igneous rock, zircon also appears in the gravel and sand produced as igneous rock erodes. In this form, it is often mixed with silica, ilmenite, and rutile. The vast majority of the zircon used in industry today originates in these sand and gravel deposits, from which the purest zircon is extracted and refined to be used as zirconium metals. Less pure deposits are used in the form of stabilized zirconia for refractories and ceramic products. The world's largest zircon mines are in Australia, South Africa, and the United States, but rich beds also exist in Brazil, China, India, Russia, Italy, Norway, Thailand, Madagascar, and Canada. Like zircon, baddeleyite is extracted from sand and gravel deposits. Unlike zircon, commercially viable baddeleyite deposits contain relatively high concentrations of zirconium oxide, and baddeleyite can thus be used without refining. The mineral is, however, much more scarce than zircon, with significant amounts occurring only in Brazil and Florida.

Extraction and Refining

Extracting zircon

• The sand and gravel that contain zircon mixed with silicate, ilmenite, and rutile are typically collected from coastal waters by a floating dredge, a large steam shovel fitted on a floating barge. After the shovel has scooped up the gravel and sand, they are purified by means of spiral concentrators, which separate on the basis of density. The ilmenite and rutile are then removed by magnetic and electrostatic separators. The purest concentrates of zircon are shipped to end-product manufacturers to be used in metal production, while less pure concentrations are used for refractories.

Refining zircon

• End-product manufacturers of zircon further refine the nearly pure zircon into zirconium by using a reducing agent (usually chlorine) to purify the metal and then sintering (heating) it until it becomes sufficiently ductile—workable—for industrial use. For small-scale laboratory use, zirconium metal may be produced by means of a chemical reaction in which chloride is used to reduce the zircon.
• The less-pure zircon is made into zirconia, an oxide of zirconium, by fusing the zircon with coke, iron borings, and lime until the silica is reduced to silicon that alloys with the iron. The zirconia is then stabilized by heating it to about 3,095 degrees Fahrenheit (1,700 degrees Celsius), with additions of lime and magnesia totalling about five percent.

Refining baddeleyite

• As mentioned above, baddeleyite contains relatively high, pure concentrations of zirconium oxide that can be used without filtering or cleansing. The only refining process used on baddeleyite involves grinding the gravel or sand to a powder and sizing the powder with different sized sieves. All zirconium oxide that comes from baddeleyite is used for refractories and, increasingly, advanced ceramics.

Quality Control

The quality control methods implemented in the production of zirconium metal are typical Statistical Process Control (SPC) methods used in most metal production. These involve tracking and controlling specific variables determined by the end product requirements. Stringent government quality control is applied to all zirconium metal produced for nuclear applications. These controls assure that the zirconium produced for use in a nuclear plant has been processed correctly and also allow for accountability: processing is tracked so that it can be traced back to each individual step and location.

Quality control methods for zirconium used in refractory applications also focus on SPC. However, in the refractory industries, it is also necessary to ascertain the beach (and even what part of the beach) from which the zirconium mineral was extracted. Manufacturers need to know exactly where the zirconium came from because each source contains slightly different trace elements, and different trace elements can affect the end product.

Byproducts/Waste

Silicate, ilmenite, and rutile—all byproducts of the zircon refining process—are typically dumped back in the water at the extraction site. These elements compose typical beach sand and are in no way detrimental to the environment. Magnesium chloride, the only other notable byproduct of zirconium manufacturing, results from the reduction of the zircon with chlorine in the refining process and is typically sold to magnesium refineries. No byproducts or waste result from baddeleyite refining.

The Future

Many believe that the future of zirconium lies in its use as an advanced ceramic. Advanced ceramics—also called "fine," "new," "high-tech," or "high-performance" ceramics—are generally used as components in processing equipment, devices, or machines because they can perform many functions better than competing metals or polymers. Zirconium is fairly hard, doesn't conduct heat well, and is relatively inert (i.e., it doesn't react readily with other elements), all excellent qualities for advanced ceramics. Zirconium oxide, manufactured as a ceramic, can be used to make crucibles for melting metals, gas turbines, liners for jet and rocket motor tubes, resistance furnaces, ultra-high frequency furnaces, and refractories such as the facing of a high-temperature furnace wall.

Where To Learn More

Books

Heuer, A. H., ed. Science and Technology of Zirconia. American Ceramic Society, 1981.

Specifications for Zirconium and Zirconium Alloy Welding Electrodes and Rods. American Welding Society, 1990.

Zirconium and Hafnium. Gordon Press Publishers, 1993.

Periodicals

Burke, Marshall A. "Ceramics Enter the Foundry," Design News. June 16,1986, p. 56.

"Fuel Cell's Future Gets a Boost," Design News. August 18, 1986, p. 38.

"Zirconium," Machine Design. April 14, 1988, pp. 234-35.

"Zirconium Holds Down Costs of Making Zirconium," Metal Progress. November, 1983, pp. 11-12.

"Adding Strength to Glassy Ceramics," Science News. September 13, 1986, p. 170.

[Article by: Alicia Haley and; Blaine Danley]

A chemical element, Zr, atomic number 40, atomic weight 91.22. Its naturally occurring isotopes are 90, 91, 92, 94, and 96. Zirconium is one of the more abundant elements, and is widely distributed in the Earth's crust. Being very reactive chemically, it is found only in the combined state. Under most conditions, it bonds with oxygen in preference to any other element, and it occurs in the Earth's crust only as the oxide, ZrO₂, baddeleyite, or as part of a complex of oxides as in zircon, elpidite, and eudialyte. Zircon is commercially the most important ore. Zirconium and hafnium are practically indistinguishable in chemical properties, and occur only together. See also Hafnium; Periodic table; Zircon.

Most of the zirconium used has been as compounds for the ceramic industry: refractories, glazes, enamels, foundry mold and core washes, abrasive grits, and components of electrical ceramics, The incorporation of zirconium oxide in glass significantly increases its resistance to alkali. The use of zirconium metal is almost entirely for cladding uranium fuel elements for nuclear power plants. Another significant use has been in photo flashbulbs.

Zirconium is a lustrous, silvery metal, with a density of 6.5 g/cm³ (3.8 oz/in.³) at 20°C (68°F). It melts at about 1850°C (3362°F). Estimates of the boiling point from appropriate data have commonly been of the order of 3600°C (6500°F), but observations suggest about 8600°C (15,500°F). The free energies of formation of its compounds indicate that zirconium should react with any nonmetal, other than the inert gases, at ordinary temperatures. In practice, the metal is found to be nonreactive near room temperature because of an invisible, impervious oxide film on its surface. The film renders the metal passive, and it remains bright and shiny in ordinary air indefinitely. At elevated temperatures it is very reactive to the non-metallic elements and many of the metallic elements, forming either solid solutions or compounds.

Zirconium generally has normal covalency of 4, and commonly exhibits coordinate covalencies of 5, 6, 7, and 8. Zirconium is at oxidation number 4 in nearly all of its compounds, Halides in which its oxidation numbers are 3 and 2 have been prepared. While zirconium is often part of cationic or anionic complexes, there is no definite evidence for a monatomic zirconium ion in any of its compounds.

Most handling and testing of zirconium compounds have indicated no toxicity. There has generally been no ill consequence of contact of zirconium compounds with the unabraded skin. However, some individuals appear to have allergic sensitivity to zirconium compounds, characteristically manifested by appearance of nonmalignant granulomas. Inhalation of sprays containing some zirconium compounds and of metallic zirconium dusts have had inflammatory effects.

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n
Zr

A metallic element with an atomic number of 40 and an atomic weight of 91.22. It is widely distributed in nature, although no concentrations are found in any one place.

For more information on zirconium, visit Britannica.com.

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A chemical element, atomic number 40, atomic weight 91.22, symbol Zr.

• z. chlorhydrate — an astringent.

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Dansk (Danish)
n. - zirkonium, zirconium

Nederlands (Dutch)
zirkoon (element 40)

Français (French)
n. - zirconium

Deutsch (German)
n. - (chem.) Zirkonium

Ελληνική (Greek)
n. - ζιρκόνιο

Italiano (Italian)
zirconio

Português (Portuguese)
n. - zircônio (m) (Quím.)

Русский (Russian)
цирконий

Español (Spanish)
n. - circonio, zirconio

Svenska (Swedish)
n. - zirkonium (kem.)

中文（简体） (Chinese (Simplified))
锆

中文（繁體） (Chinese (Traditional))
n. - 鋯

한국어 (Korean)
n. - 지르코늄(금속원소;기호Zr,번호 40)

日本語 (Japanese)
n. - ジルコニウム

العربيه (Arabic)
‏(الاسم) زركونيوم ( عنصر فلزي رمزه الكيماوي " كن)"‏

עברית (Hebrew)
n. - ‮זירקון (יסוד, RZ, מס' אטומי 04)‬

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