Stealth Technology through barium hexaferrite and ultra-fine copper powder in the paint
Since 2008, intensive research has been carried out with a wide variety of additives in a wide variety of combinations in order to develop paints that give their metallic carrier a radar-absorbing camouflage coat. In 2022, a very interesting test using barium hexaferrite and ultrafine copper powder in combination was published, which absorbed radar beams by a third. In 2023, four times as much ultrafine copper powder was suddenly sold as in the previous year.
The technique
Polymer composite materials have found their way into all areas of our lives due to their low weight and ease of processing as well as their extraordinary combination of properties. So much so that these materials can be found in space travel, aviation and even the defense industry. In this context, the use of polymer composites for radar absorption applications was discussed. Radar is an object detection system that uses electromagnetic waves to determine information such as distance, height, direction or speed of objects. This system can detect both moving objects such as airplanes, ships and automobiles as well as stationary objects such as land. Information about weather formations can also be obtained using radar. This technology, which revolutionized air and sea warfare, is one of the most important technological developments from World War II. In fact, the term RADAR was coined by the US Navy in 1940 as an abbreviation for RAdio, Detection, And Ranging. Later it gained importance not only for military and police applications, but also for flight maneuvers and detection, meteorological data collection.
If you look at how radar works, it seems to be quite simple: a signal is sent out, it bounces off an object, and this reflected signal is then picked up by some kind of receiver. This is based on the same principle as the echo of sound on a wall. However, sound is not used as a signal in the radar system, but microwaves are used. The strength of reflection and refraction of these waves depends on the properties and surface of the material from which the signal is sent. If the radar signal hits a perfectly flat surface, the signal is reflected in one direction. When it hits an uneven surface, it is reflected in multiple directions, with only a very small portion of the original signal being sent back to the receiver. Another way to reduce the reflected signal is for the signal to be absorbed by the material it passes through. The radar-absorbing materials we know have a mechanism that traps the incoming radar signals inside and prevents them from being reflected. The oldest forms of these materials were used by the Germans during World War II.
Barium hexaferrite and ultrafine copper powder were used for the production of radar-absorbing composite coatings. Barium hexaferrite powders were synthesized using the sol-gel method and used as starting material for the synthesis process. After the synthesis process, mixtures were prepared by adding barium hexaferrite and ultrafine copper powder in different amounts to a polyurethane resin (to determine the concentration dependence). By applying these mixtures to the surfaces of glass and metal substrates, coatings with a thickness of 3 mm were obtained. They were then air dried at room temperature.
Looking at the morphology of barium hexaferrite, it can be seen that it has smooth-edged, plated particles and the average particle size is about 5 μm. Copper is relatively large particles in the size range of 7-10 μm.
The radar absorption value of the sample containing 5% barium hexaferrite and 10% copper powder absorbed a maximum of 11,38%, while the absorption value of the sample with more copper increased and exceeded 12%. A maximum value can theoretically be over 80% absorption.
As for the mechanism of copper, copper does not absorb electromagnetic waves. The mechanism of radar absorption in copper is slightly different from that in barium hexaferrite. When the electromagnetic wave hits the copper surface, the electric field drives the charge carriers (electrons) to produce an alternating current. When the electromagnetic waves hit the copper surface, the free electrons oscillate with the changing electric and magnetic field, creating an electric current. The alternating current generated creates an alternating magnetic field in and around the conductor. In this case, an electromagnetic counterforce is created that forces the charge carriers to remain on the conductor surface. This means that their electromagnetic waves are absorbed by the electrons in the metal or propagate back in the same direction. At the same time, part of the electromagnetic energy is lost as heat.
Examination of these results shows that the barium ferrite and copper powder-reinforced coatings have higher magnetic saturation values than the single layers. As the amount of barium hexaferrite and copper increases, the radar absorption value increases. So the addition of barium hexaferrite and copper resulted in a good synergy in terms of increasing the absorption power. This synergy is due to the fact that the additives contribute separately to the composite with their magnetic and electrical properties. Thus, the mechanism of each additive was activated and the radar absorption performance was increased in different ways.
The market of copper powders
Copper powder is increasingly produced in Russia, Canada and Chile. In Canada and Chile, biological, almost round powder is mostly produced, which is also at home in pharmaceutical applications. In Russia, copper powder is almost exclusively produced for technological applications.
With the (warm) war that Russia started against Ukraine in 2022, the market has changed in many areas of global trade. Western banks only occasionally accept transfers that come from the sale of Russian goods. Thousands of Russian companies have restructured themselves and dismantled their companies in Russia and rebuilt them in neighboring countries, simply moved their machines or even started anew abroad. As a result, today we see copper powder producers along the Russian border from Estonia to Kazakhstan.
Since most producers of ultrafine metallic powders are our customers, we are in a fairly good position to monitor the market for ultrafine copper powders. We have increasingly seen large quantities being sold. In 2018, we estimated global trade at around 20 tonnes. In 2023 we alone will have seen over 60 tonnes change hands. This means that a current annual trading volume of around 100 tonnes can be assumed.
Since the need for copper powder in other areas of application has not increased to the same extent in the last five years, we are assuming a new player - the military. The well-known areas of application for copper powder are: electronics, semiconductors, antibacterial coatings, 3D printing, pharmaceuticals, paint manufacturers. For the military, the possible applications would be almost limitless. Everything from satellites to troop carriers could be invisible to modern radars. This tactical advantage could be worth billions of dollars to the world's military. We will continue to monitor the market and report back.
ISE AG – April 2024
