In 1925, the Germans A.E.Van Arkel and J.H. Deboer first used the thermal separation of iodide to produce the metal hafnium. The hafnium produced by iodide thermal dissociation method is of high purity and can meet the purity requirements of atomic energy industry, but it has been gradually replaced by other methods because of its small production capacity, high energy consumption and high cost.
In 1940, W.J.Kroll, a Luxemburg scientist, invented a method to produce titanium sponge by reducing titanium tetrachloride with magnesium. Because of the similar properties of hafnium tetrachloride and titanium tetrachloride, magnesium reduction method is also used in the production of hafnium and becomes the main production method of the metal hafnium.
The separation of zirconium and hafnium technology is also developing. In 1950, western countries began to use two processes provided by the United States Atomic Energy Commission to produce atomic grade sponge hafnium. In the early 1970s, the boiling chlorination process of zirconium was successfully developed. At the end of 1970s, various countries carried out research on process improvement, among which France proposed fire separation process through 10 years of research. Later, Japan developed the process of extracting zirconium and hafnium in sulfuric acid solution with trioctanamine (known as N235 in China) after alkali fusion of zirconite. Now, zirconium and hafnium separation technology can be roughly divided into wet separation and fire separation of two kinds, the successful application of fire technology in industrial production is zirconium hafnium molten salt distillation method, wet technology is solvent extraction method.
With the development of hafnium production technology, the yield and application range of hafnium are increasing. In the 1950s, the reactor of the first U.S. nuclear-powered submarine first used hafnium as control rod. In the 1980s the United States used an average of 26 tons of hafnium a year for nuclear reactors, mainly for naval and aerospace purposes.
