Zirconium is a highly corrosion-resistant, high-melting-point metal that, because of its extremely low neutron-absorption cross section, has become a key material for the nuclear industry. Its most important use is as nuclear-reactor fuel cladding: zirconium alloys (such as Zircaloy) jacket uranium dioxide fuel pellets, retaining structural integrity for long periods in high-temperature, high-pressure water while absorbing almost no neutrons so that the chain reaction proceeds efficiently; for this reason, fuel assemblies in nuclear power plants are almost universally made of zirconium alloys. In ceramics and refractories, zirconia (ZrO2) is hard and tough, and zirconia ceramics are used for dental crowns, cutting tools, watch cases and precision structural components. In refractories, zircon bricks and zircon ramming mixes line the critical zones of glass furnaces and steel melting furnaces, withstanding high-temperature erosion and slag attack. Zirconium is also used in corrosion-resistant chemical equipment, bulletproof armor, spark plugs and special welding materials, its chemical inertness performing superbly in strong acids and alkalis.
ZrSiO4, i.e. zircon sand, is the main mineral from which zirconium and hafnium are extracted; as such it is itself used in large quantities as a refractory aggregate and ceramic opacifier in glass, furnaces and wall/floor tiles. Zirconia (ZrO2), after yttria stabilization, is made into zirconia ceramics used in structural parts, dental restorations and solid-oxide fuel-cell electrolytes, and is also the main raw material for synthetic gemstones. Zirconium tetrachloride (ZrCl4) is the key intermediate for making zirconium metal and zirconium chemicals; in nuclear-grade sponge-zirconium production it is obtained by chlorinating zircon sand and then magnesium-reduced to sponge zirconium. It is worth noting that hafnium, which accompanies zircon sand, is similar in chemistry to zirconium but strongly neutron-absorbing; nuclear-grade zirconium must have hafnium deeply removed, the most critical step in zirconium processing.
