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The Technology

Polymer composites have become an integral part of modern life due to their light weight, ease of processing, and exceptional combination of properties. They are now found in aerospace, aviation, and even defense industries. In this context, the use of polymer composites for radar absorption applications has been discussed.

Radar is a detection system that uses electromagnetic waves to determine information such as the distance, altitude, direction, or speed of objects. It can detect both moving objects such as aircraft, ships, and vehicles, and stationary ones such as terrain. Radar can also be used to gather meteorological data. This technology, which revolutionized air and naval warfare, is one of the most important technological developments of World War II. In fact, the term RADAR was coined in 1940 by the U.S. Navy as an acronym for RAdio Detection And Ranging. Since then, it has gained importance not only for military and police use but also for flight navigation and weather observation.

At first glance, radar operation seems simple: a signal is emitted, it bounces off an object, and the reflected signal is received. This is similar to how an echo works—but instead of sound, radar uses microwaves. The degree of reflection and refraction depends on the properties and surface of the material hit by the signal. When a radar signal strikes a perfectly flat surface, it is reflected in one direction. When it hits an uneven surface, it is scattered in multiple directions, and only a small portion of the original signal returns to the receiver. Another way to reduce the reflected signal is through absorption of the radar waves by the material itself.

Radar-absorbing materials (RAM) have a mechanism that traps incoming radar waves within the material, preventing them from being reflected. The earliest forms of such materials were developed by the Germans during World War II.

Barium hexaferrite and ultrafine copper powder were used to produce radar-absorbing composite coatings. The barium hexaferrite powders were synthesized using the sol-gel method. After synthesis, mixtures were prepared by adding barium hexaferrite and ultrafine copper powder in various amounts to a polyurethane resin (to determine the dependence on concentration). These mixtures were then applied to glass and metal substrates, producing coatings about 3 mm thick, which were dried at room temperature in air.

The morphology of barium hexaferrite shows smooth-edged, plate-like particles with an average particle size of about 5 μm. The copper particles are relatively large, between 7–10 μm.

The radar absorption of the sample containing 5% barium hexaferrite and 10% copper powder reached a maximum of 11.38%, while increasing the copper content further boosted absorption beyond 12%. Theoretically, maximum absorption could exceed 80%.

As for the mechanism of copper, copper itself does not absorb electromagnetic waves. The radar absorption mechanism in copper differs slightly from that in barium hexaferrite. When electromagnetic waves strike the copper surface, the electric field drives free electrons, generating an alternating current. These oscillating electrons create a magnetic alternating field in and around the conductor. This generates an electromagnetic counterforce that confines the charge carriers to the surface of the conductor. Thus, the electromagnetic waves are either absorbed by the electrons or reflected in the same direction, with some of the electromagnetic energy dissipated as heat.

Analysis of the results shows that coatings reinforced with barium ferrite and copper powder exhibit higher magnetic saturation values than single-component coatings. As the amounts of barium hexaferrite and copper increase, radar absorption also increases. The addition of barium hexaferrite and copper therefore creates a synergistic effect, enhancing absorption performance. This synergy arises because the additives contribute independently through their magnetic and electrical properties—each activating different mechanisms that together improve radar absorption.

The Copper Powder Market

Copper powder is primarily produced in Russia, Canada, and Chile. In Canada and Chile, mostly biologically derived, nearly spherical copper powder is made, often used in pharmaceutical applications. In Russia, nearly all copper powder production is for technological uses.

With the (hot) war Russia began against Ukraine in 2022, global trade patterns changed dramatically. Western banks now rarely process payments related to Russian goods. As a result, thousands of Russian companies restructured—relocating operations, moving machinery abroad, or restarting under new names in neighboring countries. Consequently, we now see copper powder producers operating along the Russian border, from Estonia to Kazakhstan.

Because most producers of ultrafine metallic powders are our clients, we are in a good position to monitor the market for ultrafine copper powder. We have seen increasingly large volumes traded. In 2018, global trade was estimated at around 20 tonnes. By 2023, we alone observed over 60 tonnes changing hands, suggesting a current annual market volume of roughly 100 tonnes.

Since demand in other known application areas of copper powder has not grown nearly as much in the past five years, we suspect the emergence of a new player — the military. Known applications for copper powder include: electronics, semiconductors, antibacterial coatings, 3D printing, pharmaceuticals, and paint production.

For the military, the potential applications are virtually limitless. From satellites to armored vehicles, anything could be made invisible to modern radar systems. Such a tactical advantage could be worth billions of U.S. dollars to the world’s militaries.

We will continue to monitor this market and report again.

HF • Atomic Number 72

• History

  Hafnium was discovered in 1923 by Dutch physicist Dirk Coster and Hungarian-Swedish chemist George Charles von Hevesy. They identified it in zirconium minerals from Norway and Greenland by analyzing their X-ray spectra. The element was named after the Neo-Latin name for Copenhagen, Hafnia, the city where it was discovered.

  The discovery history of hafnium involved a long search. Dmitri Mendeleev had predicted in 1869 an element with properties similar to titanium and zirconium. Many scientists searched unsuccessfully, including Georges Urbain and Henry Moseley. Misinterpretations led to false claims of discovery, such as “Celtium” in 1911, which was later identified as lutetium.

  In the 1940s, the U.S. nuclear industry began using hafnium for control rods in nuclear reactors because, unlike zirconium, hafnium strongly absorbs neutrons.

• Application

  The largest application area for hafnium is the aerospace industry. It is used in superalloys for components such as engines and in the form of hafnium-containing coatings for high-temperature components.

  Another significant consumer of hafnium is the nuclear power industry. Due to its high neutron absorption cross-section and excellent mechanical properties, hafnium is used in control rods in nuclear reactors.

  Hafnium also plays a role in microelectronics and the semiconductor industry. In capacitors, hafnium is used as a high-k dielectric. It can replace silicon dioxide, enabling thinner insulating layers, which improves the performance and miniaturization of semiconductor devices.

  New findings regarding the properties of hafnium oxide suggest that these materials could play a key role in the development of new memory technologies. Due to the ferroelectricity of hafnium oxide, data can be stored for extended periods without power. These memory applications could pave the way for larger and faster computer systems by reducing the heat generated through continuous data transfer to volatile memory.

• Occurence, Mining and Extraction

  The most important minerals for the commercial extraction of hafnium are zircon and baddeleyite, which occur as by-products during the extraction of titanium minerals. In nature, hafnium is always bound to zirconium compounds and is difficult to separate.

  Due to the strong chemical similarity between hafnium and zirconium, separating the two elements from each other is very complex and expensive. The preferred methods for separating hafnium and zirconium are ion exchange and solvent extraction techniques. However, for some applications, separation of the two elements is not necessary.

  The main producing countries for hafnium-containing zirconium minerals are Australia and South Africa, where they are obtained from mineral sands and river gravels. By far the largest reserves are located in Australia.

  The Australian mining company Iluka Resources is the world's largest producer of zirconium ores, followed by the US company Tronox and the British-Australian mining corporation Rio Tinto.

  Framatome, a subsidiary of the French electricity company EDF, dominates the market for nuclear-grade hafnium. Allegheny Technologies Incorporated is the leading US manufacturer of hafnium for the aerospace and nuclear industries, producing highly pure hafnium for turbine blades.

  China National Nuclear Corporation is China's largest producer of hafnium.

  Chepetsky Mechanical Plant, a subsidiary of the state-owned corporation Rosatom, is an important Russian manufacturer supplying hafnium for the domestic nuclear and defense industries.

  In 2024, the global sales volume of hafnium (Hf) is estimated at around 80 tons; however, the exact quantity cannot be determined with certainty due to secrecy in the nuclear and military sectors.

  Developments in the electronics industry, increased investments in the defense sector, and the expansion of nuclear power plants are driving the growing demand for hafnium.

• Substitution

  In alloys, hafnium can be replaced by magnesium, cobalt, chromium, niobium, and tantalum. In certain superalloys, hafnium is interchangeable with zirconium.
  In control rods of nuclear reactors, boron or cadmium-silver-indium alloys can be used instead of metallic hafnium.