Zirconium

History

Klaproth discovered zirconium oxide in 1789 while investigating a semiprecious gemstone mined in Sri Lanka. The gemstone was a modification of the mineral zircon. Klaproth named the element zirconium from the Arabic word zargun, meaning gold color. The element was first prepared in an impure form by Berzelius in 1824 by reduction of potassium zirconium fluoride, K2ZrF6 with potassium. Lely and Hamburger in Germany produced high purity zirconium in 1914 by reducing resublimed zirconium tetrachloride, ZrCl4, with highly pure sodium. Very pure metal was produced by van Arkel and de Boer in 1925 by decomposition of zirconium iodide, ZrI4.
Zirconium is found in small amounts widely spread throughout nature, occurring in many alluvial deposits of lake and stream beds and ocean beaches. The most important mineral is zircon, or zircon orthosilicate, ZrSiO4. Other zirconium minerals are eudialite, (Na, Ca, Fe)6ZrSi6O18(OH, Cl), and baddeleyite, ZrO2. It also occurs in monazite sand. The abundance of zirconium in the earth’s crust is estimated as 165 mg/kg.

Uses

The most important applications of zirconium involve its alloys, Zircaloy. The alloy offers excellent mechanical and heat-transfer properties and great resistance to corrosion and chemical attack. This, in conjunction with the fact that zirconium has a low neutron absorption cross section, makes this alloy a suitable choice as a construction material for thermal nuclear reactors and nuclear power plants. Other uses are as an ingredient of explosive mixtures, as “getter” in vacuum tubes, and in making flash bulb, flash powder (historical), and lamp filaments, in rayon spinnerets, and in surgical appliances.

Reactions

Zirconium exhibits quadrivalency in most of its compounds although divalent and trivalent compounds also exist. Zirconium reacts with oxygen to form zirconium oxide, ZrO2. In powder form, Zr metal ignites spontaneously forming oxide. Solid metal, however, is stable in air at ordinary temperatures, but reacts slowly at 200°C. Reaction is rapid at high temperatures.
Reaction with hydrogen occurs at temperatures of 300 to 1,000°C forming a brittle dihydride, ZrH2. Zirconium combines with halogens at high temperatures forming tetrahalides. Reactions occur in the range 200 to 400°C. Solid tetrahalides sublime above 300°C.
Zirconium combines with nitrogen at 400°C. The reaction becomes rapid above 800°C. The product is zirconium nitride, ZrN. Some nitrogen also dissolves in the metal forming a solid state solution. Zirconium at elevated temperatures combines with most other nonmetals forming binary compounds, including sulfur, phosphorus, and carbon. Although stable to most acids, the metal is attacked by concentrated hydrochloric and sulfuric acids under boiling conditions, aqua regia, and hydrofluoric acid. The metal is stable in organic acids under all conditions. Also, the metal is stable to caustic alkalies.
The metal reacts rapidly with carbon dioxide above 1,000°C forming zirconium oxide and zirconium carbide:
2Zr + CO2 → ZrO2 + ZrC
A similar reaction occurs with carbon monoxide above 800°C forming zirconium oxide and carbide.

Description

Zirconium, is a metallic element with a grayish, crystalline scale or gray amorphous powder form. It is flammable or explosive in the form of a powder or dust and as borings and shavings. The powder should be kept wet in storage. Zirconium is a suspected carcinogen, with a TLV of 5 mg/m3 of air and it is insoluble in water. The four-digit UN identification numbers depend on the form and the amount of water present. The number for zirconium, dry, as wire, sheeting, or in the form of strips is 2009. The number for zirconium, dry, as a wire, sheeting, or as strips that are thinner than 254 μm, but not thinner than 18 μm, is 2858. Dry zirconium metal powder is 2008. Wet zirconium powder is 1358. Zirconium metal in a liquid suspension is 1308. The primary uses are as a coating on nuclear fuel rods, photo flashbulbs, pyrotechnics, explosive primers, and laboratory crucibles.

Chemical Properties

Zirconium is a grayish-white, lustrous metal in the form of platelets, flakes, or a bluish-black, amorphous powder. It has a negligible vapor pressure, and is insoluble in water, especially as zirconium oxide. The primary valence state is 4+. Zirconium and its alloys react violently with strong acids and are incompatible with strong metal alkalis and strong oxidizers but are inert to most weak acids and alkalis. Pure zirconium powder may explode spontaneously in air, while zirconium hydrides react with water to produce a flammable gas. Zirconium tetrachloride is highly corrosive, which hydrolyzes in water to form zirconyl chloride.

Physical properties

Zirconium can be a shiny grayish crystal-like hard metal that is strong, ductile, and malleable,or it can be produced as an undifferentiated powder. It is reactive in its pure form.Therefore, it is only found in compounds combined with other elements—mostly oxygen.Zirconium-40 has many of the same properties and characteristics as does hafnium-72, whichis located just below zirconium in group 4 of the periodic table. In fact, they are more similarthan any other pairs of elements in that their ions have the same charge (+4) and are of thesame general size. Because zirconium is more abundant and its chemistry is better knownthan hafnium’s, scientists extrapolate zirconium’s properties for information about hafnium.This also means that one “twin” contaminates the other, and this makes them difficult toseparate.
Zirconium’s melting point is 1,852°C, its boiling point is 4,377°C, and its density is 6.506g/cm³.

Isotopes

Zirconium has 37 isotopes, ranging from Zr-79 to Zr-110. Four of them arestable, and one is a naturally radioactive isotope, with a very long half-life. All five contribute to the element’s natural existence on Earth. The stable isotopes are the following:Zr-90 = 1.45%, Zr-91 = 11.22%, Zr-92 = 17.15%, and Zr-94 = 17.38%. The one naturalradioactive isotope is considered stable: Zr-96, with a half-life of 2.2 × 10+19 years,contributes 2.80% to zirconium’s total existence on Earth. All of the other isotopes are artificially radioactive and are produced in nuclear reactors or particle accelerators. They have half-lives ranging from 150 nanoseconds to 1.53 × 10⁺⁶ years.

Origin of Name

The name “zirconium” was derived from the Arabic word zargun, which means “gold color.” Known in biblical times, zirconium mineral had several names (e.g., jargoon, jacith, and hyacinth). Later, the mineral was called “zirconia,” and the element was later named “zirconium.”

Occurrence

Zirconium is not a rare element. It is found over most of Earth’s crust and is the 18th mostabundant element, but it is not found as a free metal in nature.
It is found in the ores baddeleyite (also known as zirconia) and in the oxides of zircons,elpidite, and eudialyte.

Characteristics

Zirconium is insoluble in water and cold acids. Although it is a reactive element, it resistscorrosion because of its rapid reaction with oxygen, which produces a protective film of zirconiumoxide (ZrO₂) that protects any metal with which it is coated. Zirconium is best knownas the gemstone zircon. Although there are different types of zircons, the most recognized isthe hard, clear, transparent zircon crystal that has a very high index of refraction, which meansit can bend light at great angles. These zircon crystals (zirconium sulfate, ZrSiO₄) are cut withfacets to resemble diamonds.
Another characteristic that makes zirconium useful is the production of “zircaloy,” whichdoes not absorb neutrons as does stainless steel in nuclear reactors. Thus, it is ideal to makenuclear fuel tubes and reactor containers. Zircaloy is the blend (alloy) of zirconium and anyof several corrosion resistant metals.

History

The name zircon may have originated from the Syriac word zargono, which describes the color of certain gemstones now known as zircon, jargon, hyacinth, jacinth, or ligure. This mineral, or its variations, is mentioned in biblical writings. These minerals were not known to contain this element until Klaproth, in 1789, analyzed a jargon from Sri Lanka and found a new earth, which Werner named zircon (silex circonius), and Klaproth called Zirkonerde (zirconia). The impure metal was first isolated by Berzelius in 1824 by heating a mixture of potassium and potassium zirconium fluoride in a small iron tube. Pure zirconium was first prepared in 1914. Very pure zirconium was first produced in 1925 by van Arkel and de Boer by an iodide decomposition process they developed. Zirconium is found in abundance in S-type stars, and has been identified in the sun and meteorites. Analyses of lunar rock samples obtained during the various Apollo missions to the moon show a surprisingly high zirconium oxide content, compared with terrestrial rocks. Naturally occurring zirconium contains five isotopes. Thirty-one other radioactive isotopes and isomers are known to exist. Zircon, ZrSiO4, the principal ore, is found in deposits in Florida, South Carolina, Australia, South Africa, and elsewhere. Baddeleyite, found in Brazil, is an important zirconium mineral. It is principally pure ZrO2 in crystalline form having a hafnium content of about 1%. Zirconium also occurs in some 30 other recognized mineral species. Zirconium is produced commercially by reduction of the chloride with magnesium (the Kroll Process), and by other methods. It is a grayish-white lustrous metal. When finely divided, the metal may ignite spontaneously in air, especially at elevated temperatures. The solid metal is much more difficult to ignite. The inherent toxicity of zirconium compounds is low. Hafnium is invariably found in zirconium ores, and the separation is difficult. Commercial-grade zirconium contains from 1 to 3% hafnium. Zirconium has a low absorption cross section for neutrons, and is therefore used for nuclear energy applications, such as for cladding fuel elements. Commercial nuclear power generation now takes more than 90% of zirconium metal production. Reactors of the size now being made may use as much as a half-million lineal feet of zirconium alloy tubing. Reactor-grade zirconium is essentially free of hafnium. Zircaloy? is an important alloy developed specifically for nuclear applications. Zirconium is exceptionally resistant to corrosion by many common acids and alkalis, by sea water, and by other agents. It is used extensively by the chemical industry where corrosive agents are employed. Zirconium is used as a getter in vacuum tubes, as an alloying agent in steel, in surgical appliances, photoflash bulbs, explosive primers, rayon spinnerets, lamp filaments, etc. It is used in poison ivy lotions in the form of the carbonate as it combines with urushiol. With niobium, zirconium is superconductive at low temperatures and is used to make superconductive magnets. Alloyed with zinc, zirconium becomes magnetic at temperatures below 35 K. Zirconium oxide (zircon) has a high index of refraction and is used as a gem material. The impure oxide, zirconia, is used for laboratory crucibles that will withstand heat shock, for linings of metallurgical furnaces, and by the glass and ceramic industries as a refractory material. Its use as a refractory material accounts for a large share of all zirconium consumed. Zirconium tungstate is an unusual material that shrinks, rather than expands, when heated. A few other compounds are known to possess this property, but they tend to shrink in one direction, while they stretch out in others in order to maintain an overall volume. Zirconium tungstate shrinks in all directions over a wide temperature range of from near absolute zero to +777°C. It is being considered for use in composite materials where thermal expansion may be a problem. Zirconium of about 99.5% purity is available at a cost of about $2000/kg or about $4/g.

Uses

It is used in lamp filaments; flash bulbs;vacuum tubes and in explosives. It is alsoused as a structural material for nuclearreactors.

Uses

About 90% of all the zirconium produced in the United States is used in the nuclearelectrical power industry. Since it does not readily absorb neutrons, it is a desired metal inthe manufacture of nuclear reactors and their fuel tubes, but it must be free of its “twin”hafnium for these purposes. Zirconium is also used as an alloy with steel to make surgicalinstruments.
Zirconium dioxide (ZrO₂) as an abrasive is used to make grinding wheels and specialsandpaper. It is also used in ceramic glazes, in enamels, and for lining furnaces and hightemperature molds. It resists corrosion at high temperatures, making it ideal for crucibles and other types of laboratory ware. ZrO₂ is used as a “getter” to remove the last trace of air when producing vacuum tubes.
As mentioned, zircon (ZrSiO₄) has many forms, but the most used is the transparent crystalthat is cut to resemble a diamond. There is even one form of zirconium used in medicine: zirconiumcarbonate (3ZrO₂?CO₂?H₂O), which, as a lotion, can be used to treat poison ivy infections.
When zirconium is alloyed with niobium, it becomes superconductive to electricity attemperatures near absolute zero Kelvin (–273°C).

Uses

Pure zirconium (hafnium-free) is a valuable structural material for atomic reactors because of its low nuclear cross-section and high corrosion and heat resistance. Because of hafnium's high neutron absorption characteristics, it must be removed from zirconium which is to be used in nuclear reactors; removal unnecessary for other commercial purposes. As an ingredient of priming or explosive mixtures; flashlight powders; as deoxidizer in metallurgy; as "getter" in vacuum tubes; in constructing rayon spinnerets in lamp filaments, flash bulbs.

Production Methods

Zirconium was first produced in elemental form in 1824 by Berzelius, but it was brittle because it contained impurities such as oxygen, nitrogen, and hydrogen. In 1914, the first relatively pure zirconium was prepared by reducing zirconium tetrachloride with sodium in a bomb furnace. Highpurity zirconium was produced by Van Arkel and de Boer in 1925 by vaporizing zirconium tetraiodide into a bulb containing a hot tungsten filament, which caused the tetraiodide to dissociate, depositing zirconium on the filament. The zirconiumisrecoveredas brightextremelypuremetalcrystals.This procedure was later used for the commercial production of zirconium in the United States. Dr. Kroll from the Bureau of Mines conducted research and produced high-purity zirconium on a commercial scale in 1944; the Kroll method is now used for large-scale commercial production of zirconium.
In 2009, resources of zircon in the United States included about 14 million tons associated with titanium resources in heavy-mineral sand deposits. Phosphate and sand and gravel deposits have the potential to yield substantial amount of zircon as a future by-product. Eudialyte and gittinsite are zirconium silicate minerals that have a potential for zirconia production. Currently, identified world resources of zircon exceed 60 million tons.
The production of zirconium metal must be carried out in an atmosphere from which water vapor, oxygen, and nitrogen are rigorously excluded; otherwise, the metal becomes brittle and impossible to fabricate.

Definition

zirconium: Symbol Zr. A grey-whitemetallic transition element; a.n. 40;r.a.m. 91.22; r.d. 6.49; m.p. 1852°C;b.p. 4377°C. It is found in zircon (ZrSiO4; the main source) and in baddeleyite(ZnO2). Extraction is by chlorinationto give ZrCl4 which ispurified by solvent extraction and reducedwith magnesium (Krollprocess). There are five natural isotopes(mass numbers 90, 91, 92, 94,and 96) and six radioactive isotopesare known. The element is used innuclear reactors (it is an effectiveneutron absorber) and in certain alloys.The metal forms a passive layerof oxide in air and burns at 500°C.Most of its compounds are complexesof zirconium(IV). Zirconium(IV) oxide(zirconia) is used as an electrolyte infuel cells. The element was identifiedin 1789 by Klaproth and was first isolatedby Berzelius in 1824.

General Description

A gray amorphous sludge with not less than 20% water.

Air & Water Reactions

May ignite on contact with air or moist air. May burn rapidly with flare-burning effect. Some react vigorously or explosively on contact with water. The severity of the pyrophoric reaction depends a great deal on zirconium particle size, with the finely divided material reacting with the most vigor. The initiation of the explosion has been spark and by electrostatic ignition. Zirconium dusts have been known to explode, [NFPA 482M, 1974], covers all aspects of storage and handling of zirconium, there are 43 abstracts of unusual zirconium fire and explosion incidents. Water Insoluble .

Reactivity Profile

When a mixture of alkali hydroxides and zirconium is heated, the liberated oxygen reacts explosively with zirconium [Mellor 7:116 1946-47]. Chromates, dichromates, sulfates, molybdates, and tungstates of lithium, sodium, potassium, rubdium, and cesium will react violently, even explosively, with an excess of zirconium powder [Ellern 1968. p. 249]. A mixture of hydrated borax and zirconium explodes when heated [Mellor 7:116 1946-47]. An explosion occurred when zirconium sponge was placed in a beaker of carbon tetrachloride [Allison 1969]. Zirconium explodes violently with cupric oxide or lead oxide [Mellor 7:116 1946-47]. A mixture of powdered zirconium and potassium nitrate explodes when heated above the melting point [Mellor 7:116 1946-47].

Hazard

There is disagreement relative to the dangers of the elemental form of zirconium. Some saythat the metal and gemstone forms are harmless, but there is some evidence that the vapors andpowder forms of the metal may be carcinogenic. Also, several zirconium compounds can produceallergic reactions in humans and have proven to be toxic to the skin or lungs if inhaled.
The fine powder and dust of zirconium are explosive, especially in the presence of nonmetalsthat oxidize these forms of zirconium.

Health Hazard

The toxicity of zirconium and its compoundshas been found to be of low order. Lethal dosein rabbits when administered intravenouslyis reported as 150 mg/kg (Lewis(Sr) 1996).Inhalation of dust of the metal or its compoundscan form skin and pulmonary granulomasthat may be attributed to reaction ofsensitized T cells with antigen. X-ray studiesin animals indicate retention of the metal inthe lungs. Inhalation may produce irritationof mucous membrane. Skin contact can causeirritation.

Fire Hazard

May react violently or explosively on contact with water. Some are transported in flammable liquids. May be ignited by friction, heat, sparks or flames. Some of these materials will burn with intense heat. Dusts or fumes may form explosive mixtures in air. Containers may explode when heated. May re-ignite after fire is extinguished.

Flammability and Explosibility

Contact with water liberates highly flammable gases

Safety Profile

A very dangerous fire hazard in the form of dust when exposed to heat or flame or by chemical reaction with oxidizers. May ignite spontaneously. A dangerous explosion hazard in the form of dust by chemical reaction with air, alkali hydroxides, alkali metal chromates, dichromates, molybdates, sulfates, tungstates, borax, CCl4, CuO, Pb, PbO, P, KClO3, KNO3, nitrylfluoride. Explosive range: 0.16 g/L in air. To fight fire, use special mixtures, dry chemical, salt, or dry sand. See also ZIRCONIUM COMPOUNDS.

Potential Exposure

Zirconium is never found in the free state; the most common sources are the ores zircon and baddeleyite. It is generally produced by reduction of the chloride or iodide. The metal is highly reactive; the process is usually performed under an inert gas blanket. Zirconium metal is used as a “getter” in vacuum tubes, a deoxidizer in metallurgy; a substitute for platinum; it is used in priming of explosive mixtures; flashlight powders; lamp filaments; flash bulbs; and construction of rayon spinnerets. Zirconium or its alloys (with nickel, cobalt, niobium, tantalum) are used as lining materials for pumps and pipes, for chemical processes, and for reaction vessels. Pure zirconium is a structural material for atomic reactor; and alloyed, particularly with aluminum, it is a cladding material for fuel rods in water-moderated nuclear reactors. A zirconium-columbium alloy is an excellent superconductor. Zircon (ZrSiO4) is utilized as a foundry sand, an abrasive; a refractory in combination with zirconia; a coating for casting molds; a catalyst in alkyl and alkenyl hydrocarbon manufacture; a stabilizer in silicone rubbers; and as a gem stone; in ceramics it is used as an opacifier for glazes and enamels and in fritted glass filters. Both zircon and zirconia (zirconium oxide, ZrO2) bricks are used as linings for glass furnaces. Zirconia itself is used in die extrusion of metals and in spout linings for pouring metals, as a substitute for lime in oxyhydrogen flam; as a pigment; and an abrasive; it is used, too, in incandescent lights; as well as in the manufacture of enamels, white glass; and refractory crucibles. Other zirconium compounds are used in metal cutting tools, thermocouple jackets; waterproofing textiles; ceramics, and in treating dermatitis and poison ivy.

Shipping

UN2008 Zirconium powder, dry, Hazard Class: 4.2; Labels: 4.2-Spontaneously combustible material. UN1358 Zirconium suspended in a liquid, Hazard Class: 3; Labels: 3-Flammable liquid. UN1358 Zirconium powder, wetted with not <25% water (a visible excess of water must be present) (1) mechanically produced, particle size <53 μm; (2) chemically produced, particle size <840 μm, Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN 1932 Zirconium scrap, Hazard Class: 4.2; Labels: 4.2- Spontaneously combustible material. UN 2009 Zirconium, dry, finished sheets, strip or coiled wire, Hazard Class: 4.2; Labels: 4.2-Spontaneously combustible material. UN2858 Zirconium, dry, coiled wire, finished metal sheets, strip (thinner than 254 μm but not thinner than 18 μm), Hazard Class: 4.1; Labels: 4.1-Flammable solid.

Incompatibilities

Dust may form explosive mixture with air. Violent reactions with oxidizers, air, alkali hydroxides; alkali metal compounds (such as chromates, dichromates, molybdates, salts; sulfates, and tungstates); borax, carbon tetrachloride; lead, lead oxide; phosphorus, potassium compound s. Incompatible with boron, carbon, nitrogen, halogens, lead, platinum, potassium nitrate. Powder may ignite spontaneously and can continue burning under water. Explodes if mixed with hydrated borax when heated. Fine powder may be stored completely immersed in water.