What is zirconium?
Zirconium is a chemical element or silvery-white, hard, and high melting transition metal of Group 4 (IVB) of the periodic table with the symbol Zr and atomic number 40. It is placed in d-block elements with group members titanium and hafnium. It is used for making bullet-proof steel and other corrosion-resistant alloys. The zirconium mineral zircon occurs in a beautiful range of colour like golden, orange, and pink. These are used in gemstones from the early days of human civilization. The most common oxidation number or state of zirconium is +4 (IV). The lower oxidation states of the metal are less common.
Who discovered zirconium?
The mineral zircon has two main forms like hyacinth and jargon. The early analysis showed it was the oxides of silicon, iron, aluminum, and calcium. In 1789, the German chemist Klaproth discovered the new element from zircon and named it zirconium. But the crude metal was first extracted in 1824 by Berzelius. The pure Zr metal was obtained by the van Arkel process in 1925.
Properties of zirconium
The atomic number of zirconium is 40 and the electronic configuration [Kr] 3d2 4s2. The metal is fairly electropositive from dioxide on heating. The massive metal at room temperature is resistant to corrosion.
It dissolves only in hot concentrated sulfuric acid, aqua regia, and hydrofluoric acid. Hot aqueous alkali does not attack this transition metal. Some common properties of zirconium are given below the table,
|Properties of Zirconium
|Electron per shell||2, 8, 18, 10, 2|
|Electronic configuration||[Kr] 4d2 5s2|
|Melting point||2128 K (1855 °C, 3371 °F)|
|Boiling point||4650 K (4377 °C, 7911 °F)|
|Crystal structure||hexagonal close-packed (hcp)|
|Molar heat capacity||25.36 J mol-1K-1|
|Electrical resistivity||421 nΩ·m|
|Atomic radius||160 pm|
|Covalent radius||175±7 pm|
|Common oxidation number||+4|
|Electronegativity||Pauling scale: 1.33|
|Ionization energy (kJ/mol)||1st||2nd||3rd|
Where is zirconium found?
It is quite abundant metal ranking after transition metals iron, titanium, and manganese. It contains 0.016 percent or 162ppm of the earth’s crust. The principal commercial source of zirconium is zircon (ZrSiO4) and Baddeleyite (ZrO2). The minerals are found widely in Australia, Brazil, India, Russia, South Africa, and the United States.
It has five isotopes like 90Zr, 91Zr, 92Zr 94Zr, and 96Zr. The longest live radioactive isotope of zirconium is 96Zr (2.4×1019 years). Twenty-eight artificial isotopes of the metal ranging from atomic mass 78 to 110 can be prepared by different types of nuclear reactions.
It is produced by the Kroll process. The minerals are converted to chloride by heating with carbon and chlorine. The tetrachloride is reduced with molten magnesium. Very pure zirconium is produced by the van Arkel process. The metal is heated with iodine in an evacuated vessel at 200°C. The volatile ZrI4 decomposes on an electrically heated filament at 1300 °C. The hafnium content has been reduced below 100ppm which can be achieved by solvent extraction or ion exchange methods.
Interesting facts about zirconium
Zirconium oxide (ZrO2) is the most common solid oxide with a high melting point. It is insoluble in water, cold dilute acids (except HF), and alkalis. It reacts with acids slowly when heated for a long time and with alkali on fusion. ZrO2 is used in making refractory crucibles and furnace linings. The white gelatinous hydroxide precipitate is obtained by adding alkali to Zr(IV) solution.
All the four tetrahalides of zirconium are known and prepared by heating metal with halogens. All the halides are white solids. The unit cell of solid ZrF4 involves 2:8 coordination. In the ZrF4 unit, each Zr atom is surrounded by eight fluorine ions in a square antiprism configuration. The tetrahalides are vigorously hydrolysis at room temperature produced oxohalides which are stable to further hydrolysis.
Zirconium (IV) nitrate, sulfate are the basic salts of the metal. The sulfate compound is formed by dissolving ZrO2 in hot concentrated sulfuric acid. The anhydrous nitrate may be prepared by reacting N2O5 on ZrCl4.
The large Zr+4 ion shows high coordination numbers and formed a variety of coordination complexes. Some coordination complexes of zirconium are given below the table,
|Oxidation state||Co-ordination number||Geometry||Examples|
|+4 (IV)||6||octahedral||Li2[ZrF6]; [Zr(acac)2Cl2]|
|8||square antiprism||[ZrF8]-4; [Zr(acac)4]|
|dodecahedral||[Zr(ox)4]-4; [ZrX4(diars)2]; [Zr4(OH)8(H2O)16]+8|
A few unstable hydrocarbon derivatives like Li[Zr(Me)6] have been isolated from the reaction of LiMe and ZrCl4 at low temperatures. Zr(benzyl)4 is a stable and homogeneous chemical catalyst in the Ziegler-Natta process. Cyclopentadine (Cp) forms a number of important compounds comparable to that of titanium. These are used as homogeneous catalysts for the production of many organic compounds.
Uses of Zirconium
- Zirconium is a very low absorption of thermal neutrons but it may be free from traces of hafnium which absorbed neutrons 600 times more. Therefore, it is the ideal material used in nuclear power stations. The annual production of nuclear grade hafnium-free zirconium is all time high of about 165 tonnes. It is used to manufacture seamless coolant tubes for eight heavy water reactors.
- Zirconium is used in making bullet-proof alloy steels and other corrosion-resistant alloys. In many chemical plants and stainless steel, it is preferred over titanium. Zr-Sn alloys are used in the cooler of nuclear reactors.
- Due to the corrosion resistance properties towards acids and alkalis, it is widely used in the chemical industry.
- Like titanium, it is used in pumps, valves, heat exchangers, pipings, etc. With niobium, it is used for making superconducting magnets. It is used as a scavenger in the steel industry which removes dissolved oxygen and nitrogen.
- For the production of blue and yellow pigments, the mineral zircon is mixed with vanadium and praseodymium.
- Zirconium(IV) oxide is used in making refractory crucibles, furnace linings, foundry bricks, abrasives, glass, and ceramics industries.
Analysis of zirconium metal
Zirconium precipitated in routine quantitative analysis of Group-3 or Group-IIIA metals. On the addition of hydrogen peroxide (H2O2), a white precipitate of Zr peroxide (ZrO2, xH2O) has appeared. Alizarin-S gives a red precipitate with the solution of metal in a strongly acid medium. The colour is discharged by the action of fluoride. Zirconium also formed a very characteristic phosphate Zr(HPO4)2 even from the solution which contains 10 percent sulfuric acid.