The Application of Zirconium and Its Alloys
Zirconium was discovered by Klaproth in 1789 and it is usually extracted from zircon ores together with hafnium. The properties of zirconium indicate that it is ductile and has useful mechanical properties similar to those of austenitic stainless steel and titanium. Zirconium has excellent corrosion resistance to many acids, alkalies, organic compounds, and salt solutions except for few media such as hydrofluoric acid, ferric or cupric chloride, aqua regia, concentrated sulfuric acid, and moist chlorine gas. Besides zirconium is transparent to thermal energy neutrons. Zirconium has very low thermal neutron capture cross section of 0.18 barns, compared to that of hafnium of 113 barns (neutron absorption). Today, a high proportion of ziconium is used in water-cooled nuclear power reactors; the second large use is the chemical processing equipment. Hafnium always coexists with zirconium naturally. When used for nuclear applications, they must be separated from each other: zirconium, that is transparent to thermal energy neutrons may be used for fuel cladding; hafnium, which has a high-capture cross section for thermal energy neutrons has found use in nuclear reactor control rods. Additional uses of zirconium and its alloys are in flashbulbs, incendiary ordnance, and gettering contaminating gases in sealed devices such as vacuum tubes.
For nuclear reactor applications, there are four grades of ziconium and its alloys available (all with hafnium separated/removed): Reactor Grade Zirconium (UNS R60001), Zircaloy-2 (UNS R60802), Zircaloy-4 (UNS R60804), Zr-2.5Nb (UNS R60901). For chemical processing & industrial applications, the hafnium-containing commercial grades of zirconium includes: Zr700 (UNS R60700) – low oxygen zirconium, Zr702 (UNS R60702) – unalloyed zirconium, Zr704 (UNS R60704) – zirconium-tin, Zr705 (UNS R60705) – zirconium-niobium, Zr706 (UNS R60706) – zirconium-niobium.