Where Is Hafnium Found? Occurrence and Extraction Explained
What is Hafnium?
Hafnium can be described as a chemical element with an atomic number 72 and the symbol Hf. It is a silvery gray, lustrous, tetravalent transition metal. This element chemically resembles zirconium and is found in various zirconium minerals. In 1869, the existence of this element was predicted by Dmitri Mendeleev, even though it was not previously identified by Coster and Hevesy until 1923, making it the last stable element to be discovered. The hafnium element is named after Hafnia, which is the Latin name for Copenhagen, where it was discovered. The hf element name is Hafnium.
Hafnium is used in electrodes and filaments. A few semiconductor fabrication processes use its oxide for the integrated circuits at 45 nm and smaller feature lengths. Some of the superalloys, that are used for any of the special applications contain hafnium in combination with the elements like titanium, tungsten, or niobium.
Hafnium Properties
Let us discuss a few physical and chemical hafnium properties in detail.
Physical Properties of Hafnium
Hafnium is a shiny and silvery metal that exhibits ductile features.
Usually, it is resistant to corrosion and exhibits similar chemical properties as zirconium. This similarity is due to valence electrons' presence, which is the same and that of the same group.
A thin protective layer film is formed on the metal when reacted with water, which shows corrosion occurrences.
The impurities that are present in the zirconium highly affect the hafnium metal. Therefore, both are considered to be the most inseparable.
There is no acid effect over the metal, but still, when ignited in the presence of oxygen, the metal produces oxides. This metal is highly resistant to a few concentrated alkalis.
Approximately 5.8 ppm of the earth's upper crust layer constitutes this metal, and this metal does not exist freely in the environment.
Chemical Properties of Hafnium
Hafnium reacts in the air to form a protective film that inhibits further corrosion. Acids do not readily attack this element, but it can be burnt in the air or oxidized with halogens. Similar to its sister metal, zirconium, finely divided hafnium can combust spontaneously in the air, and is therefore very resistant to concentrated alkali.
The chemistry of zirconium and hafnium is similar, where the two cannot be separated based on different chemical reactions.
The solubility in solvents and the melting and boiling points of the compounds are the primary differences in these twin elements' chemistry.
Occurrence of Hafnium
Hafnium is estimated to make up nearly 5.8 ppm of the upper crust of Earth by mass. It does not remain as a free element on the Earth. Instead, this metal can be found with a combination of a solid solution with natural zirconium compounds such as ZrSiO₄, zircon, which usually has about 1-4% of the Zr replaced by the Hf. In rare cases, the Hf/Zr ratio increases during crystallization to form isostructural mineral hafnon (Hf, Zr)SiO₄, with atomic Hf > Zr. Alvite is an obsolete name for zircon varieties containing unusually high Hf content.
Applications of Hafnium
Let us look at some of the applications of hafnium in various industries.
Most of the produced hafnium is used in the control rod manufacture for the nuclear reactors.
Many details add to the fact that there are only some technical uses for hafnium. Firstly, the close similarity between zirconium and hafnium makes it possible to use zirconium for many applications; as the next one, in the late 1950s, hafnium was first available as a pure metal after the nuclear industry usage for hafnium-free zirconium.
Moreover, the difficult separation techniques and low abundance necessary make it a scarce commodity. In 2014, when zirconium’s demand has dropped following the Fukushima disaster, the hafnium element’s price increased sharply from ＄500–600/kg to up to ＄1000/kg in 2015.
Production of Hafnium
The titanium ores' heavy mineral sands ore deposits rutile and ilmenite yield most of the mined zirconium, and then, as well as most of the hafnium.
Zirconium is also one of the good nuclear fuel-rod cladding metals, including the desirable properties of good chemical stability, and holds a very less neutron capture cross-section, taken at high temperatures. Due to the neutron-absorbing properties of hafnium, zirconium impurities will usually allow it to be much less useful for any nuclear-reactor use. Therefore, approximately, a complete separation of hafnium and zirconium is required for their use in nuclear power. Hafnium-free zirconium production is the major source of hafnium.
Precautions
Care should be taken when machining the hafnium metal because it is pyrophoric, and the fine particles can combust spontaneously when exposed to the air. Many people rarely encounter compounds that contain hafnium. This pure metal is not considered to be toxic. However, hafnium compounds should be handled carefully as if they were toxic. The metal's ionic forms are usually at the greatest risk for toxicity, and limited animal testing has been done for these compounds.
People can be exposed to the workplace's hafnium element by swallowing, breathing, eye contact, and skin contact. And, the Occupational Safety & Health Administration - OSHA, has set the legal limit (which is the Permissible exposure limit) for exposure to hafnium and its compounds in the workplace with TWA 0.5 mg/m³ up to an 8-hour workday. Also, the National Institute for Occupational Safety & Health - NIOSH has also set the same REL (Recommended Exposure Limit) at 50 mg/m³ levels; hafnium is immediately dangerous to health and life.
Did you know?
Hafnium elements contain a unique property of capturing neutrons. Thus, it can be used in the reactors' control rods and nuclear submarines as well.
It can be utilized widely in the microprocessors because they are involved in the leakage current reduction.
Its compounds are used in the alloy and ceramic industries since they carry higher melting points.
In the plasma cutting process, this metal serves as an electrode because it gives out electrons.
It can also be used in gas-filled lamps and incandescents.
FAQs on Hafnium: Properties, Uses, and Importance
1. What is hafnium and where is it located in the periodic table?
Hafnium (symbol Hf, atomic number 72) is a lustrous, silvery, and ductile transition metal. It is located in Group 4 and Period 6 of the periodic table, placing it in the d-block. Chemically, it is very similar to zirconium, which is positioned directly above it in the same group.
2. What are the most important physical and chemical properties of hafnium?
Hafnium is known for several key properties that make it valuable in various high-tech industries. Its most notable properties include:
High Melting Point: It has a very high melting point of 2,233 °C, making it stable at extreme temperatures.
Corrosion Resistance: It forms a tough, passive oxide layer on its surface, which provides excellent resistance to corrosion from acids and alkalis.
Neutron Absorption: Hafnium has a very high thermal neutron absorption cross-section, meaning it is exceptionally good at capturing neutrons.
Ductility: Pure hafnium is soft and ductile, allowing it to be easily worked and drawn into wire.
3. Why are hafnium and zirconium so chemically similar and difficult to separate?
The remarkable similarity between hafnium and zirconium is a direct consequence of the lanthanide contraction. As you move across the lanthanide series (elements 57-71), which precedes hafnium, the atomic radii decrease due to the poor shielding effect of the 4f electrons. This contraction effectively cancels out the expected increase in atomic size down the group. As a result, hafnium (Period 6) has an atomic radius almost identical to that of zirconium (Period 5). Since chemical properties are largely governed by atomic size and valence electrons, their near-identical radii make them behave almost identically in chemical reactions, rendering their separation a complex and difficult process.
4. Why is hafnium an excellent material for control rods in nuclear reactors?
Hafnium is an ideal material for control rods in nuclear submarines and power plants primarily due to its exceptional ability to absorb neutrons. The rate of a nuclear fission reaction depends on the number of available neutrons. Hafnium's high neutron-capture cross-section allows it to effectively absorb surplus neutrons, thereby slowing down or stopping the chain reaction. This property, combined with its excellent strength and corrosion resistance under the high-temperature, high-pressure conditions inside a reactor, makes it a reliable and safe choice for controlling nuclear processes.
5. How is hafnium's high melting point utilized in industrial applications like plasma torches?
The extremely high melting point of hafnium (2,233 °C) makes it highly resistant to heat and deformation. This property is critical in applications like plasma welding and cutting torches. The electrode in a plasma torch must withstand the intense heat of the plasma arc, which can reach thousands of degrees Celsius. Hafnium's ability to endure these temperatures without melting or degrading ensures the electrode's longevity and the stability of the plasma arc, making it a crucial component in high-temperature metal fabrication.
6. Explain the importance of hafnium compounds in the manufacturing of modern microprocessors.
Hafnium-based compounds, particularly hafnium oxide (HfO₂), are vital in the semiconductor industry. As transistors in microprocessors become smaller, the traditional silicon dioxide (SiO₂) insulator becomes too thin and allows current to leak, wasting power and generating excess heat. Hafnium oxide is a 'high-k' dielectric, meaning it can store more charge at the same thickness. This allows manufacturers to use a physically thicker insulating layer that prevents current leakage while achieving the same electrical performance as a much thinner SiO₂ layer. This innovation was critical for creating smaller, faster, and more power-efficient integrated circuits from the 45 nm generation onwards.
7. Beyond nuclear reactors, what makes hafnium a critical element in superalloys used in aerospace?
In the aerospace industry, hafnium is a critical addition to nickel-based superalloys used for making high-performance components like jet engine turbine blades. When added in small quantities (around 1-2%), hafnium significantly improves the alloy's properties by strengthening the grain boundaries. This prevents a phenomenon called creep—the tendency of a material to deform under high temperature and stress over time. By reinforcing the alloy's structure, hafnium enhances its overall strength, ductility, and resistance to high-temperature fatigue, which is essential for the safety and efficiency of modern aircraft engines.
