Zirconium is a shiny
gray-white metal similar to the other elements in group 4 of the
Periodic Table: titanium and hafnium.
Zirconium metal is steel gray and is in pure form a soft and malleable metal with a high melting point (2125 oC). The metal can be easily drawn into thin threads and rolled into foils. Up to 863 ° C, the crystal structure of zirconium metal is hexagonal densest spherical packing. Above that temperature, the structure is less densely packed (cubic room-centered).
The metal can dissolve significant amounts of oxygen (up to 30 atomic percent), nitrogen and hydrogen, and small amounts of these make the metal more brittle.
Zirconium metal is resistant to air at normal temperatures as it is covered by a thin layer of oxide (such as aluminum). Only at temperatures above approx. At 400 ° C, a rapidly increasing oxidation of the metal is obtained with the formation of an oxide shell of zirconia, ZrO2, at the same time as oxygen is dissolved in the metal. This makes zirconium metal unsuitable as a high temperature material.
The metal is very corrosion resistant below 400 oC. It is not attacked by water, dilute hydrochloric acid and sulfuric acid, phosphoric acid and organic acids, lye and other. It also works well against molten alkalis. Zirconium reacts at higher temperatures with the halogens (for example chlorine), sulfur, carbon, silicon and others with the formation of halides, sulphides, carbides and silicides.
In their chemical compounds, zirconium has oxidation numbers –II, 0, I, II, III and IV. The latter is the most common and stable under normal conditions.
In powder or as a porous sponge, the surface area is large, and the metal is therefore easily ignited in air already at about 200 ° C, possibly at a lower temperature by rubbing or discharging static electricity. It must therefore be treated carefully and stored under argon, in methanol and other. Because the powder reacts with both water vapor and carbon dioxide, the ignited powder must be extinguished by covering with dry sand or salt.
Zirconium has a very low impact cross-section for thermal neutrons (0.184 children), and zirconium is therefore used as an encapsulation material for fuel elements in nuclear power plants. The effect cross section is much larger for hafnium (104 children), so the metal used for fuel elements must not contain more than 0.01% hafnium. (Hafnium is used instead in the form of rods to control the neutron flux in the nuclear power plant.) The two elements are separated by different methods, where extraction with organic solvents is the most common.
Zirconium-containing sand is concentrated and then melted with coke in electric arc furnaces at about 3500 ° C. This forms zirconium carbide and zirconium carbide nitride. After crushing, these are converted by treatment with chlorine gas to zirconium tetrachloride. .
Reduce the zirconium tetrachloride with magnesium (possibly together with sodium) in the absence of air (oxygen and nitrogen) in the curling process: ZrCl4 (g) + 2Mg (s) → Zr (s) + 2MgCl2 (s). The magnesium chloride and residues of magnesium metal are removed by distillation in vacuo and the residue becomes zirconium metal in a sponge-like form. This is melted by arc or electron beam melting in vacuo. Metal that is free of oxygen and nitrogen is produced by thermal decomposition of zirconium tetraiodide, ZrI4, according to the van Arkel-de Boer method (see Anton Eduard van Arkel).
Zirconium is used as an alloy additive to many metals and alloys such as steel, magnesium and aluminum. Magnesium – zinc – zirconium alloys are distinguished by high mechanical strength and low weight and are used in the aerospace industry, among other places. The metal is also used as a deoxidizing agent, but then in the form of ferrozirconium, ferrosilicon zirconium and other.
About 90% of the zirconium metal produced in the world is used for capsules for fuel elements (of uranium dioxide, UO2) in nuclear reactors, then in the form of an alloy (zircalloy). This use is due to the good corrosion of the metal
|99.99%, （4N）Zr Sheet||99.99%, （4N）Zr Foil|