Hafnium is a transition metal that is a grey steel color in its natural solid state. It is resistant to corrosion, but it reacts with halogens. Hafnium has an atomic weight of 178.49, a melting point of 4051 °F, and a boiling point of 8317 °F. Hafnium is most commonly used as a component in control rods for nuclear reactors. Other uses of hafnium include: as a component in incandescent lamps, as a component in certain types of metal alloys, and in the process of plasma cutting.
Hafnium does not occur free in its natural state; it usually occurs in nature with minerals that contain zirconium such as alvite, thortveitite, and pegmatites.
The isolation process of hafnium is extremely complicated as it is difficult to separate it from zirconium. These two elements have almost identical chemical characteristics and isolating the two elements is only performed on a commercial basis. Hafnium was originally separated from zirconium using repeated recrystallization processes of its double ammonium or potassium fluoride compounds. It can also be isolated by passing the vapor of hafnium in its tetra-iodide form over a heated tungsten filament.
Hafnium can also be isolated from zirconium using the Kroll process. In this process, hafnium (IV) chloride is reduced with magnesium or sodium compounds. The Kroll process uses pyrometallurgical processes on an industrial bases for the extraction of titanium and zirconium; the byproduct of zirconium using the Kroll process is hafnium. During this process, the ore is reduced with coke from petroleum sources in a fluidized bed reactor and heated to 1832 °F. Further processes using magnesium or chloride extract the zirconium from the hafnium.
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