Zirconium alloy in the context of Zirconium hydride

⭐ Core Definition: Zirconium alloy

Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. One of the main uses of zirconium alloys is in nuclear technology, as cladding of fuel rods in nuclear reactors, especially water reactors. A typical composition of nuclear-grade zirconium alloys is more than 95 weight percent zirconium and less than 2% of tin, niobium, iron, chromium, nickel and other metals, which are added to improve mechanical properties and corrosion resistance.

The water cooling of reactor zirconium alloys elevates requirement for their resistance to oxidation-related nodular corrosion. Furthermore, oxidative reaction of zirconium with water releases hydrogen gas, which partly diffuses into the alloy and forms zirconium hydrides. The hydrides are less dense and are weaker mechanically than the alloy; their formation results in blistering and cracking of the cladding – a phenomenon known as hydrogen embrittlement.

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Zirconium alloy in the context of Hafnium

Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1922 by Dirk Coster and George de Hevesy. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered. The element is obtained only by separation from zirconium, with most of the world's hafnium production coming from processes that also produce zirconium. These processes make use of heavy mineral sands ore deposits, which include the minerals zircon, rutile, and ilmenite, among others.

Hafnium is most often used in alloys with nickel, and was used in larger quantities to produce the control rods used in nuclear reactors. Hafnium's large neutron capture cross section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors. It is ductile, and is also used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nanometres (1.8×10 in) and smaller, and superalloys used for special applications can contain hafnium in combination with niobium, titanium, or tungsten.

View the full Wikipedia page for Hafnium

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