The Diversity Applications of Hafnium Metal

Most of the hafnium produced is used in the manufacture of control rods for nuclear reactors.[28]

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Standards:

Hafnium has limited technical applications due to a few factors. First, it's very similar to zirconium, a more abundant element that can be used in most cases. Second, pure hafnium wasn't widely available until the late 1950s when it became a byproduct of the nuclear industry's need for hafnium-free zirconium.

Applications:

Nuclear reactors

The nuclei of several hafnium isotopes can each absorb multiple neutrons. This makes hafnium a good material for nuclear reactors' control rods. Its neutron capture cross section (Capture Resonance Integral Io ≈ 2000 barns)[59] is about 600 times that of zirconium (other elements that are good neutron-absorbers for control rods are cadmium and boron). Excellent mechanical properties and exceptional corrosion-resistance properties allow its use in the harsh environment of pressurized water reactors.[28] The German research reactor FRM II uses hafnium as a neutron absorber.[60] It is also common in military reactors, particularly in US naval submarine reactors, to slow reactor rates that are too high.[61][62] It is seldom found in civilian reactors, the first core of the Shippingport Atomic Power Station (a conversion of a naval reactor) being a notable exception.[63]

Alloys

The hafnium-containing rocket nozzle of the Apollo Lunar Module in the lower right corner

Hafnium is used in alloys with iron, titanium, niobium, tantalum, and other metals. An alloy used for liquid-rocket thruster nozzles, for example, the main engine of the Apollo Lunar Modules, is C103 which consists of 89% niobium, 10% hafnium, and 1% titanium.[64]

Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys. It thereby improves corrosion resistance, especially under cyclic temperature conditions that tend to break oxide scales, by inducing thermal stresses between the bulk material and the oxide layer.[65][66][67]

Microprocessors

Hafnium-based compounds are employed in gates of transistors as insulators in the 45 nm (and below) generation of integrated circuits from Intel, IBM, and others.[68][69] Hafnium oxide-based compounds are practical high-k dielectrics, allowing reduction of the gate leakage current which improves performance at such scales.[70][71][72]

Isotope geochemistry

In most geologic materials, zircon is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in geology.[77] Hafnium is readily substituted into the zircon crystal lattice and is therefore very resistant to hafnium mobility and contamination. Zircon also has an extremely low Lu/Hf ratio, making any correction for initial lutetium minimal. Although the Lu/Hf system can be used to calculate a "model age", i.e. the time at which it was derived from a given isotopic reservoir such as the depleted mantle, these "ages" do not carry the same geologic significance as do other geochronological techniques as the results often yield isotopic mixtures and thus provide an average age of the material from which it was derived.

Garnet is another mineral that contains appreciable amounts of hafnium to act as a geochronometer. The high and variable Lu/Hf ratios found in garnet make it useful for dating metamorphic events.

Other uses

Due to its heat resistance and its affinity to oxygen and nitrogen, hafnium is a good scavenger for oxygen and nitrogen in gas-filled and incandescent lamps. Hafnium is also used as the electrode in plasma cutting because of its ability to shed electrons into the air.[79]

The high energy content of 178m2Hf was the concern of a DARPA-funded program in the US. This program eventually concluded that using the above-mentioned 178m2Hf nuclear isomer of hafnium to construct high-yield weapons with X-ray triggering mechanisms-an application of induced gamma emission-was infeasible because of its expense. See hafnium controversy.

Hafnium metallocene compounds can be prepared from hafnium tetrachloride and various cyclopentadiene-type ligand species. Perhaps the simplest hafnium metallocene is hafnocene dichloride. Hafnium metallocenes are part of a large collection of Group 4 transition metal metallocene catalysts [80] that are used worldwide in the production of polyolefin resins like polyethylene and polypropylene.

A pyridyl-amido hafnium catalyst can be used for the controlled iso-selective polymerization of propylene which can then be combined with polyethylene to make a much tougher recycled plastic.

Hafnium diselenide is studied in spintronics thanks to its charge density wave and superconductivity.