The Hardworking Element Hafnium

Introduction to Hafnium

Identified in 1923 by Dirk Coster and George de Hevesy, hafnium is a lustrous, silver-grey transition metal. The name “hafnium” originated from Hafnia, the Latin name for Copenhagen, which is where hafnium was discovered. Hafnium chemically resembles zirconium, as they have the same number of valence electrons and are in the same group, and hafnium is in many zirconium minerals like zircon and baddeleyite. This element has significant commercial applications, mainly in nuclear power industries, ceramics, alloys, and electronics. 

Ten Interesting and Fun Facts About Hafnium

1. One physical difference between hafnium and zirconium is their density. Zirconium has approximately half the density of hafnium.
2. Separating hafnium and zirconium is incredibly difficult because of their similar chemical properties. Therefore, most commercial hafnium is a byproduct of refining zirconium. 
3. Hafnium is unaffected by water, air, all alkalis, and all acids except for HF (hydrofluoric acid).
4. Commercial sources of minerals containing hafnium are in the United States, Australia, Brazil, India, and western Africa.
5. Hafnium compounds and alloys have extremely high melting points since hafnium is very heat-resistant. For example, hafnium carbide (HfC) has a melting point of 3890°C, and the tantalum hafnium carbide alloy (Ta₄HfC₅) has a melting point of around 4125°C. 
6. Dimitri Mendeleev predicted the existence of the element hafnium in 1869 (over 50 years before hafnium’s discovery) and believed there would be an element that is similar to but heavier than zirconium and titanium. 
7. Scientists have identified hafnium vapor in the Sun’s atmosphere.
8. Hafnium produces a protective film of nitride or oxide on exposed surfaces, making the element highly resistant to corrosion. 
9. The element can form alloys with iron, tantalum, titanium, and other transition metals. 
10. Hafnium ignites spontaneously in powder form, similar to zirconium.

Hafnium in the Periodic Table

Hafnium’s symbol is Hf, with atomic number 72 and an atomic mass of 178.486. This means that there are 72 protons within the nucleus of a hafnium atom and 72 electrons around its nucleus in its neutral state. It is located on the d-block of the periodic table, with lutetium on its left and tantalum on its right. It is a transitional metal in group 4 and period 6. Hafnium has an electron configuration of [Xe]6s²4f¹⁴5d² and four valence electrons. On the Pauling scale, hafnium has a medium-low electronegativity of 1.33.

Hafnium in Today’s World

Applications of Hafnium

Since hafnium is very corrosion- and heat-resistant and a good absorber of neutrons, the element has many applications in industries and technologies. Hafnium is useful in nuclear submarines and nuclear reactor control rods, a critical technology to maintain fission reactions, because it absorbs neutrons well. Zirconium, on the other hand, does not absorb neutrons well and is therefore used in fuel rods where neutrons must be able to pass through easily. Hence, you must completely separate the hafnium from zirconium-hafnium alloys to use zirconium for these rods. 

Hafnium may be in cathodes, ceramics, photography flash bulbs, light bulb filaments, and other electronic equipment. 

You may make hafnium alloys with titanium, iron, niobium, and tantalum, which can result in very heat-resistant alloys for engineering applications. Hafnium carbide, specifically, can line high-temperature furnaces and kilns because of hafnium’s high heat resistance. 

Current Research with Hafnium

Researchers are still investigating hafnium’s use in nuclear power industries and electronics, but there have been interesting developments in applying the element to cancer treatments. The clinical translation of hafnium oxide or NBTXR3 may be implemented as a nanoradiosensitizer for the radiotherapy of cancers. Researchers are currently attempting to synthesize these hafnium-based nanomaterials, as they could possibly improve disease diagnosis and treatment. 

Hafnium Compounds

Halides

Hafnium (IV) chloride (HfCl₄) and hafnium (IV) iodide (HfI₄) have applications in the production and purification of hafnium metal. They are volatile solids that are precursors to various organohafnium compounds. Hafnium (IV) fluoride (HfF₄) has a few applications in optical coating and semiconductor industries and as catalysts.

Oxides 

Hafnium (IV) oxide (HfO₂), also known as hafnia, is a colorless solid that is also used in optical coatings and as a refractory material because of its high melting point. 

Other compounds

The compound hafnium diboride (HfB₂) is a refractory ceramic, with high thermal and electrical conductivities. 

Hafnium carbide (HfC) is the most refractory binary compound, and hafnium nitride is the most refractory of all known metal nitrides. 

The compound hafnium disulfide (HfS₂) can be produced by reacting hydrogen sulfide and hafnium oxide at high temperatures.

Hafnium Oxidation States

The most common oxidation state of hafnium is +4. 

Isolation of Elemental Hafnium

Chemists Anton Eduardo van Ariel and Jan Hendrik created a new method for producing hafnium in 1925. They decomposed hafnium (IV) iodide on a hot tungsten wire, resulting in a crystal bar of pure hafnium. This is the crystal bar process. 

Another method is the liquid-liquid extraction process. Using a variety of solvents, the by-product of separating zirconium from hafnium-zirconium alloys is hafnium (IV) chloride. Hafnium (IV) chloride is then converted to the element hafnium by reduction with sodium or magnesium.

Properties of Hafnium

• Symbol: Hf
• Melting point: 2233°C
• Boiling point: 4600°C
• Density (g cm-3): 13.3
• Atomic mass: 178.486 amu
• Atomic number: 72
• Electronegativity: 1.33
• Classification: Transition metal
• Natural abundance of Hafnium in the earth’s crust: 3.0 ppm
• Electron shell configuration: [Xe] 4f¹⁴5d²6s² 
• Isotopes: The isotopes of hafnium are ¹⁷⁷Hf, ¹⁷⁸Hf, ¹⁸⁰Hf 
• Minerals: Hafnium is in the minerals zircon (ZrSiO₄) at a ratio of 50:1 (zirconium to hafnium) and baddeleyite (ZrO₂) at a ratio of 73:1 (zirconium to hafnium)
• Toxicity: Hafnium is generally non-toxic.

Where Can I Buy the Element Hafnium?

You can buy slightly impure hafnium metal online, but the pure form of hafnium is rare and expensive because it is difficult to separate from minerals.