Facts About Hafnium
Facts About Hafnium
The paramagnetic metal with the symbol Hf is a silvery-gray shiny metal. The transition metal is located in Group 4 of the periodic table. The properties of hafnium are very similar to zirconium, which is located nearby in the periodic table. It is one of the last discoveries among the stable elements in the periodic table.
History of Hafnium
The chemical element hafnium was discovered in the city of Copenhagen, which bore the Latin name ‘Hafnia.’ Initial indications of the existence of an additional element arose from studies of Moseley’s law, discovered in 1912. The physicist Niels Bohr predicted in his 1922 work on atomic theory that element 72 must be similar to zirconium. Hafnium was discovered in 1923 in Norwegian zircon using X-ray spectroscopy. Further investigations revealed that hafnium is always found in zirconium-containing minerals. Jantzen and Hevesy separated hafnium from zirconium by repeatedly crystallizing diammonium and dipotassium fluorides. Elemental hafnium was obtained through reduction with sodium.
Applications of Hafnium
Due to the difficulty and cost-intensive production, this material is only used in small quantities. The primary application area is nuclear technology. Due to its reactivity with small amounts of oxygen and nitrogen, it is preferably used to remove trace amounts of these substances from ultra-high vacuum systems. When burned, hafnium emits a very bright light, making flash lamps with hafnium particularly efficient. As an alloying element in metals such as niobium, tantalum, molybdenum, and tungsten, it increases their strength.
Production of Hafnium
Hafnium is a rare element in the continental Earth’s crust, comparable to bromine and cesium. It is often found as an impurity in zircon minerals, such as zircon and allendeite, usually comprising about 2% of the zirconium content. The zircon variety alvite is one of the few minerals that contains more hafnium than zirconium. The most important deposits are in Australia and South Africa.
To separate hafnium from zircon, extraction processes are used. These processes exploit the differing solubility of specific zirconium and hafnium salts in special solvents. Fractional distillation and ion exchange are other separation methods. The separated hafnium can then be converted into hafnium chloride using the Kroll process. Elemental hafnium is obtained by reduction with sodium or magnesium. By applying the Van Arkel-de Boer process, even purer hafnium can be produced.
Hafnium of high purity is soft and ductile. These properties allow it to be rolled and forged. Impurities such as oxygen, nitrogen, or carbon make the material brittle, which makes further processing difficult. As a reactive metal, the base metal reacts with oxygen when heated. Other non-metals such as nitrogen, carbon, boron, and silicon form compounds. An oxide layer passivates the metal, protecting it from further oxidation at room temperature. Typically, due to the formed oxide layer, hafnium is resistant to acids.