Hafnium tetraiodide

Hafnium tetrabromide [13777-22-5], HfBr, is very similar to the tetrachloride in both its physical and chemical properties. Hafnium tetraiodide [13777-23-6], Hfl, is produced by reaction of iodine with hafnium metal at 300°C or higher. At temperatures above 1200°C, the iodide dissociates to hafnium metal and iodine. These two reactions are the basis for the iodide-bar refining process. Hafnium iodide is reported to have three stable crystalline forms at 263—405°C (60). 

Hfl4 HAFNIUM TETRAIODIDE 816 lnCI2 INDIUM DICHLORIDE 851... 

Hfl4[g] HAFNIUM TETRAIODIDE (GAS) 817 lnCI2[gl INDIUM DICHLORIDE (GAS) 852... 

It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungsten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). 

Derivation The ore is converted to a cyanonitride and is chlorinated to obtain zirconium tetrachloride. This is reduced with magnesium (Kroll process) in inert atmosphere. The metal can be prepared in a highly pure and ductile form by vapor-phase decomposition of the tetraiodide. Hafnium must be removed for uses in nuclear reactors... 

Zircon silicate is the most important source of hafnium. Ion-exchange and solvent-extraction techniques have supplanted fractional crystallization and distillation as the preferred methods of separating hafnium from zirconium. The metal itself is prepared by magnesium reduction of hafnium tetrachloride (the Kroll process), and by the thermal decomposition of tetraiodide (de Boer-van Arkel process). The annual world production of hafnium metal was about 40 tons at the end of the 1980s (Soloveichik... 

Titanium, zirconium, and hafnium are purified by the decomposition of their tetraiodides on a hot wire. The impure metal is heated with iodine in an evacuated flask, to produce the tetraiodide as a gas ... 

RJH Clark, BK Hunter, DM Rippon. Vapor-phase Raman spectra, force constants, and values for thermodynamic functions of the tetrachlorides, tetrabromides, and tetraiodides of titanium, zirconium, and hafnium. Inorg Chem 11 56-61, 1972. 

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