Hafnium

Hafnium Details

Hafnium Symbol: Hf

Hafnium Atomic Number: 72

Hafnium Atomic Weight: 178.49

What is Hafnium?

Hafnium (atomic number 72, symbol Hf) is a transitional metal and a chemical element, which chemically resembles zirconium. It is a silvery grey, lustrous, and ductile metal found in zirconium minerals. Hafnium is also corrosion resistant, but zirconium impurities affect its physical properties and its nuclear properties, in particular. Due to their chemical similarity, hafnium and zirconium are difficult to separate. Density is one difference between them, and the density of zirconium is around one-half that of hafnium. Other differences between zirconium and hafnium are their boiling points and melting points as well as their solubility in solvents. In terms of nuclear properties, the element has several isotopes that absorb neutrons readily.

The element was discovered by the Hungarian chemist de Hevesy and the Danish chemist Dirk Coster in 1923. The scientists employed X-ray spectroscopy to study samples of zirconium ore and the arrangement of outer electrons in hafnium. Niels Bohr predicted its electron structure while Hevesy discovered a matching pattern.

Normally, hafnium does not affect human health, but its compounds are considered toxic. Initial research suggests that the danger is limited. However, metal dust is known to pose explosion and fire hazard. The metal is not toxic itself and insoluble in body chemicals, saline solutions, and water. Exposure to the chemical can occur through skin and eye contact, ingestion, and inhalation. Overexposure to compounds of hafnium and hafnium itself causes mild irritation of the mucous membranes, skin, and eyes. No symptoms and signs of chronic exposure to the element have been observed and reported.

Given that hafnium absorbs neutrons, it is used in nuclear reactors’ control rods. As an alloying agent, the element is also used in niobium, titanium, iron, and other metals. Hafnium is employed in high-temperature ceramics and alloys because some compounds of the element are refractory. They do not melt except under very high temperature.

Two hafnium ores are known – alvite and hafnon although they are rare. Over 34 isotopes have been discovered, and their mass number ranges from 153 to 186. There are 5 stable isotopes of hafnium. Hafnium-based compounds are used in the electronics industry and in gate insulators, in particular, generating integrated circuits (IBM, Intel, and others). Compounds of hafnium, which are oxide-based, are high-k dielectrics. The gate leakage current is thus reduced, with performance at such scales being enhanced.

Given hafnium’s affinity to nitrogen and oxygen and its heat resistance, the element is a good scavenger for nitrogen and oxygen in incandescent lamps. In plasma cutting, the metal is used as an electrode because it sheds electrons into the air. A nuclear isomer of hafnium was researched as part of the US-funded program DARPA. The program assessed the possibility of using it to develop high-yield weapons with mechanisms that trigger X-rays. Because of the high costs, the use of induced gamma emission was considered infeasible.

There are a few applications of hafnium, and several factors contribute to this. The first is the similarity between zirconium and hafnium, making it possible to employ zirconium instead of hafnium in most applications. Second, the difficult separation methods and its low abundance on earth make hafnium a scarce commodity. Third, this metal was available in a pure form only in the late 50s and after its application in the nuclear industry.

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