The Application of Rare Earth Materials in Modern Military Technology

Rare earths, known as the "treasure trove" of new materials, as a special functional material, can greatly improve the quality and performance of other products, and are known as the "vitamins" of modern industry. They are not only widely used in traditional industries such as metallurgy, petrochemicals, glass ceramics, wool spinning, leather, and agriculture, but also play an indispensable role in materials such as fluorescence, magnetism, laser, fiber optic communication, hydrogen storage energy, superconductivity, etc, It directly affects the speed and level of development of emerging high-tech industries such as optical instruments, electronics, aerospace, and nuclear industry. These technologies have been successfully applied in military technology, greatly promoting the development of modern military technology.

The special role played by rare earth new materials in modern military technology has attracted high attention from governments and experts of various countries, such as being listed as a key element in the development of high-tech industries and military technology by relevant departments of countries such as the United States and Japan.

A Brief Introduction to Rare Earths and Their Relationship with Military and National Defense
Strictly speaking, all rare earth elements have certain military applications, but the most critical role they play in national defense and military fields should be in applications such as laser ranging, laser guidance, and laser communication.

The application of rare earth steel and rare earth ductile iron in modern military technology

1.1 Application of Rare Earth Steel in Modern Military Technology

The function includes two aspects: purification and alloying, mainly desulfurization, deoxidation, and gas removal, eliminating the influence of low melting point harmful impurities, refining grain and structure, affecting the phase transition point of steel, and improving its hardenability and mechanical properties. Military science and technology personnel have developed many rare earth materials suitable for use in weapons by utilizing the properties of rare earth.

1.1.1 Armor steel

As early as the early 1960s, China's weapons industry began to research the application of rare earths in armor steel and gun steel, and successively produced rare earth armor steel such as 601, 603, and 623, ushering in a new era of key raw materials for tank production in China based on domestic production.

1.1.2 Rare earth carbon steel

In the mid-1960s, China added 0.05% rare earth elements to a certain high-quality carbon steel to produce rare earth carbon steel. The lateral impact value of this rare earth steel is increased by 70% to 100% compared to the original carbon steel, and the impact value at -40 ℃ is nearly doubled. The large-diameter cartridge case made of this steel has been proven through shooting tests in the shooting range to fully meet technical requirements. Currently, China has finalized and put it into production, realizing China's long-standing wish of replacing copper with steel in cartridge material.

1.1.3 Rare earth high manganese steel and rare earth cast steel

Rare earth high manganese steel is used to manufacture tank track plates, while rare earth cast steel is used to manufacture tail wings, muzzle brakes, and artillery structural components for high-speed shell piercing shells. This can reduce processing steps, improve steel utilization, and achieve tactical and technical indicators.

1.2 Application of Rare Earth Nodular Cast Iron in Modern Military Technology

In the past, China's forward chamber projectile materials were made of semi-rigid cast iron made of high-quality pig iron mixed with 30% to 40% scrap steel. Due to its low strength, high brittleness, low and non sharp effective fragmentation after explosion, and weak killing power, the development of forward chamber projectile bodies was once restricted. Since 1963, various calibers of mortar shells have been manufactured using rare earth ductile iron, which has increased their mechanical properties by 1-2 times, multiplied the number of effective fragments, and sharpened the edges of the fragments, greatly enhancing their killing power. The combat shell of a certain type of cannon shell and field gun shell made of this material in our country has a slightly better effective number of fragmentation and dense killing radius than the steel shell.

The application of non-ferrous rare earth alloys such as magnesium and aluminum in modern military technology

Rare earths have high chemical activity and large atomic radii. When added to non-ferrous metals and their alloys, they can refine grain size, prevent segregation, remove gas, impurities and purify, and improve metallographic structure, thereby achieving comprehensive goals such as improving mechanical properties, physical properties, and processing performance. Domestic and foreign material workers have utilized the properties of rare earths to develop new rare earth magnesium alloys, aluminum alloys, titanium alloys, and high-temperature alloys. These products have been widely used in modern military technologies such as fighter jets, assault aircraft, helicopters, unmanned aerial vehicles, and missile satellites.

2.1 Rare earth magnesium alloy

Rare earth magnesium alloys have high specific strength, can reduce aircraft weight, improve tactical performance, and have broad application prospects. The rare earth magnesium alloys developed by China Aviation Industry Corporation (hereinafter referred to as AVIC) include about 10 grades of cast magnesium alloys and deformed magnesium alloys, many of which have been used in production and have stable quality. For example, ZM 6 cast magnesium alloy with rare earth metal neodymium as the main additive has been expanded to be used in important parts such as helicopter rear reduction casings, fighter wing ribs, and rotor lead pressure plates for 30 kW generators. The rare earth high-strength magnesium alloy BM25 jointly developed by China Aviation Corporation and Nonferrous Metals Corporation has replaced some medium strength aluminum alloys and has been applied in impact aircraft.

2.2 Rare earth titanium alloy

In the early 1970s, the Beijing Institute of Aeronautical Materials (referred to as the Institute) replaced some aluminum and silicon with rare earth metal cerium (Ce) in Ti-A1-Mo titanium alloys, limiting the precipitation of brittle phases and improving the alloy's heat resistance and thermal stability. On this basis, a high-performance cast high-temperature titanium alloy ZT3 containing cerium was developed. Compared with similar international alloys, it has certain advantages in heat resistance, strength, and process performance. The compressor casing manufactured with it is used for the W PI3 II engine, reducing the weight of each aircraft by 39 kg and increasing the thrust to weight ratio by 1.5%. In addition, the processing steps are reduced by about 30%, achieving significant technical and economic benefits, filling the gap of using cast titanium casings for aviation engines in China under 500 ℃ conditions. Research has shown that there are small cerium oxide particles in the microstructure of ZT3 alloy containing cerium . Cerium combines a portion of oxygen in the alloy to form a refractory and high hardness rare earth oxide material, Ce2O3. These particles hinder the movement of dislocations during alloy deformation, improving the high-temperature performance of the alloy. Cerium captures some gas impurities (especially at grain boundaries), which may strengthen the alloy while maintaining good thermal stability. This is the first attempt to apply the theory of difficult solute point strengthening in casting titanium alloys. In addition, after years of research, the Aviation Materials Institute has developed stable and inexpensive yttrium oxide sand and powder materials in the titanium alloy solution precision casting process, using special mineralization treatment technology. It has achieved good levels in specific gravity, hardness, and stability to titanium liquid. In terms of adjusting and controlling the performance of the shell slurry, it has shown greater superiority. The outstanding advantage of using yttrium oxide shell to manufacture titanium castings is that, under conditions where the quality and process level of the castings are comparable to that of the tungsten surface layer process, it is possible to manufacture titanium alloy castings that are thinner than those of the tungsten surface layer process. At present, this process has been widely used in the manufacturing of various aircraft, engines, and civilian castings.

2.3 Rare earth aluminum alloy

The HZL206 heat-resistant cast aluminum alloy containing rare earths developed by AVIC has superior high-temperature and room temperature mechanical properties compared to nickel containing alloys abroad, and has reached the advanced level of similar alloys abroad. It is now used as a pressure resistant valve for helicopters and fighter jets with a working temperature of 300 ℃, replacing steel and titanium alloys. Reduced structural weight and has been put into mass production. The tensile strength of rare earth aluminum silicon hypereutectic ZL117 alloy at 200-300 ℃ is higher than that of West German piston alloys KS280 and KS282. Its wear resistance is 4-5 times higher than that of commonly used piston alloys ZL108, with a small coefficient of linear expansion and good dimensional stability. It has been used in aviation accessories KY-5, KY-7 air compressors and aviation model engine pistons. The addition of rare earth elements to aluminum alloys significantly improves the microstructure and mechanical properties. The mechanism of action of rare earth elements in aluminum alloys is to form a dispersed distribution, and small aluminum compounds play a significant role in strengthening the second phase; The addition of rare earth elements plays a role in degassing and purifying, thereby reducing the number of pores in the alloy and improving its performance; Rare earth aluminum compounds, as heterogeneous crystal nuclei to refine grains and eutectic phases, are also a type of modifier; Rare earth elements promote the formation and refinement of iron rich phases, reducing their harmful effects. α— The solid solution amount of iron in A1 decreases with the increase of rare earth addition, which is also beneficial for improving strength and plasticity.

The application of rare earth combustion materials in modern military technology

3.1 Pure rare earth metals

Pure rare earth metals, due to their active chemical properties, are prone to react with oxygen, sulfur, and nitrogen to form stable compounds. When subjected to intense friction and impact, sparks can ignite flammable materials. Therefore, as early as 1908, it was made into flint. It has been found that among the 17 rare earth elements, six elements including cerium, lanthanum, neodymium, praseodymium, samarium, and yttrium have particularly good arson performance. People have turned the arson properties of rare earth metals into various types of incendiary weapons, such as the US Mark 82 227 kg missile, which uses rare earth metal lining, which not only produces explosive killing effects but also arson effects. The American air-to-ground "Damping Man" rocket warhead is equipped with 108 rare earth metal square rods as liners, replacing some prefabricated fragments. Static blasting tests have shown that its ability to ignite aviation fuel is 44% higher than that of unlined ones.

3.2 Mixed rare earth metals

Due to the high price of pure rare earth metals, various countries widely use inexpensive composite rare earth metals in combustion weapons. The composite rare earth metal combustion agent is loaded into the metal shell under high pressure, with a combustion agent density of (1.9~2.1) × 103 kg/m3, combustion speed 1.3-1.5 m/s, flame diameter of about 500 m m, flame temperature as high as 1715-2000 ℃. After combustion, the duration of the incandescent body heating is longer than 5 minutes. During the Vietnam War, the US military launched a 40mm incendiary grenade using a launcher, and the ignition lining inside was made of a mixed rare earth metal. After the projectile explodes, each fragment with a igniting liner can ignite the target. At that time, the monthly production of the bomb reached 200000 rounds, with a maximum of 260000 rounds.

3.3 Rare earth combustion alloys

A rare earth combustion alloy weighing 100 g can form 200-3000 sparks with a large coverage area, which is equivalent to the killing radius of armor piercing and armor piercing shells. Therefore, the development of multifunctional ammunition with combustion power has become one of the main directions of ammunition development at home and abroad. For armor piercing and armor piercing shells, their tactical performance requires that after penetrating enemy tank armor, they can also ignite their fuel and ammunition to completely destroy the tank. For grenades, it is required to ignite military supplies and strategic facilities within their killing range. It is reported that a plastic rare earth metal incendiary bomb made in the United States has a body made of fiberglass reinforced nylon and a mixed rare earth alloy core, which is used to have better effects against targets containing aviation fuel and similar materials.

Application of 4 Rare Earth Materials in Military Protection and Nuclear Technology

4.1 Application in Military Protection Technology

Rare earth elements have radiation resistant properties. The National Center for Neutron Cross Sections in the United States used polymer materials as the substrate and made two types of plates with a thickness of 10 mm with or without the addition of rare earth elements for radiation protection testing. The results show that the thermal neutron shielding effect of rare earth polymer materials is 5-6 times better than that of rare earth free polymer materials. The rare earth materials with added elements such as samarium, europium, gadolinium, dysprosium, etc. have the highest neutron absorption cross section and have a good effect on capturing neutrons. At present, the main applications of rare earth anti radiation materials in military technology include the following aspects.

4.1.1 Nuclear radiation shielding

The United States uses 1% boron and 5% rare earth elements gadolinium, samarium, and lanthanum to make a 600m thick radiation resistant concrete for shielding fission neutron sources in swimming pool reactors. France has developed a rare earth radiation protection material by adding borides, rare earth compounds, or rare earth alloys to graphite as the substrate. The filler of this composite shielding material is required to be evenly distributed and made into prefabricated parts, which are placed around the reactor channel according to the different requirements of the shielding parts.

4.1.2 Tank thermal radiation shielding

It consists of four layers of veneer, with a total thickness of 5-20 cm. The first layer is made of glass fiber reinforced plastic, with inorganic powder added with 2% rare earth compounds as fillers to block fast neutrons and absorb slow neutrons; The second and third layers add boron graphite, polystyrene, and rare earth elements accounting for 10% of the total filler amount to the former to block intermediate energy neutrons and absorb thermal neutrons; The fourth layer uses graphite instead of glass fiber, and adds 25% rare earth compounds to absorb thermal neutrons.

4.1.3 Others

Applying rare earth anti radiation coatings to tanks, ships, shelters, and other military equipment can have an anti radiation effect.

4.2 Application in Nuclear Technology

Rare earth yttrium oxide can be used as a combustible absorber for uranium fuel in boiling water reactors (BWRs). Among all elements,  gadolinium has the strongest ability to absorb neutrons, with approximately 4600 targets per atom. Each natural  gadolinium atom absorbs an average of 4 neutrons before failure. When mixed with fissionable uranium,  gadolinium can promote combustion, reduce uranium consumption, and increase energy output. Gadolinium oxide does not produce harmful byproduct deuterium like boron carbide, and can be compatible with both uranium fuel and its coating material during nuclear reactions. The advantage of using gadolinium instead of boron is that gadolinium can be directly mixed with uranium to prevent nuclear fuel rod expansion. According to statistics, there are currently 149 planned nuclear reactors worldwide, of which 115 pressurized water reactors use rare earth gadolinium oxide. Rare earth samarium, europium, and dysprosium have been used as neutron absorbers in neutron breeders. Rare earth yttrium has a small capture cross-section in neutrons and can be used as a pipe material for molten salt reactors. Thin foils with added rare earth gadolinium and dysprosium can be used as neutron field detectors in aerospace and nuclear industry engineering, small amounts of rare earth thulium and erbium can be used as target materials for sealed tube neutron generators, and rare earth oxide europium iron metal ceramics can be used to make improved reactor control support plates. Rare earth gadolinium can also be used as a coating additive to prevent neutron radiation, and armored vehicles coated with special coatings containing gadolinium oxide can prevent neutron radiation. Rare earth ytterbium is used in equipment for measuring the geostress caused by underground nuclear explosions. When rare earth ytterbium is subjected to force, the resistance increases, and the change in resistance can be used to calculate the pressure it is subjected to. Linking rare earth gadolinium foil deposited by vapor deposition and staggered coating with a stress sensitive element can be used to measure high nuclear stress.

5,Application of Rare Earth Permanent Magnet Materials in Modern Military Technology

The rare earth permanent magnet material, hailed as the new generation of magnetic kings, is currently known as the highest comprehensive performance permanent magnet material. It has more than 100 times higher magnetic properties than the magnetic steel used in military equipment in the 1970s. At present, it has become an important material in modern electronic technology communication, used in traveling wave tubes and circulators in artificial Earth satellites, radars, and other fields. Therefore, it has significant military significance.

Samarium cobalt magnets and neodymium iron boron magnets are used for electron beam focusing in missile guidance systems. Magnets are the main focusing devices for electron beams and transmit data to the control surface of the missile. There are approximately 5-10 pounds (2.27-4.54 kg) of magnets in each focusing guidance device of the missile. In addition, rare earth magnets are also used to drive electric motors and rotate the rudder of guided missiles. Their advantages lie in their stronger magnetic properties and lighter weight compared to the original aluminum nickel cobalt magnets.

6 .Application of Rare Earth Laser Materials in Modern Military Technology

Laser is a new type of light source that has good monochromaticity, directionality, and coherence, and can achieve high brightness. Laser and rare earth laser materials were born simultaneously. So far, approximately 90% of laser materials involve rare earths. For example, yttrium aluminum garnet crystal is a widely used laser that can achieve continuous high-power output at room temperature. The application of solid-state lasers in modern military includes the following aspects.

6.1 Laser ranging

The neodymium doped  yttrium aluminum garnet laser rangefinder developed by countries such as the United States, Britain, France, and Germany can measure distances of up to 4000 to 20000 meters with an accuracy of 5 meters. The weapons systems such as the American MI, Germany's Leopard II, France's Leclerc, Japan's Type 90, Israel's Mecca, and the latest British developed Challenger 2 tank all use this type of laser rangefinder. At present, some countries are developing a new generation of solid laser rangefinders for human eye safety, with a working wavelength range of 1.5-2.1 μ M. Handheld laser rangefinders have been developed using holmium doped yttrium lithium fluoride lasers in the United States and the United Kingdom, with a working wavelength of 2.06 μ M, ranging up to 3000 m. The United States has also collaborated with international laser companies to develop an erbium-doped  yttrium lithium fluoride laser with a wavelength of 1.73 μ M's laser rangefinder and heavily equipped with troops. The laser wavelength of China's military rangefinder is 1.06 μ M, ranging from 200 to 7000 m. China obtains important data from laser television theodolites in target range measurements during the launch of long-range rockets, missiles, and experimental communication satellites.

6.2 Laser guidance

Laser guided bombs use lasers for terminal guidance. The Nd · YAG laser, which emits dozens of pulses per second, is used to irradiate the target laser. The pulses are encoded and the light pulses can self guide the missile response, thereby preventing interference from missile launch and obstacles set by the enemy. The US military GBV-15 glider bomb, also known as the "dexterous bomb". Similarly, it can also be used to manufacture laser guided shells.

6.3 Laser communication

In addition to Nd · YAG, the laser output of lithium neodymium phosphate crystal (LNP) is polarized and easy to modulate, making it one of the most promising micro laser materials. It is suitable as a light source for fiber optic communication and is expected to be applied in integrated optics and cosmic communication. In addition,yttrium  iron garnet (Y3Fe5O12) single crystal can be used as various magnetostatic surface wave devices using microwave integration technology, making the devices integrated and miniaturized, and having special applications in radar remote control, telemetry, navigation, and electronic countermeasures.

7.The Application of  Rare Earth Superconducting Materials in Modern Military Technology

When a certain material experiences zero resistance below a certain temperature, it is known as superconductivity, which is the critical temperature (Tc). Superconductors are a type of antimagnetic material that repels any attempt to apply a magnetic field below the critical temperature, known as the Meisner effect. Adding rare earth elements to superconducting materials can greatly increase the critical temperature Tc. This greatly promotes the development and application of superconducting materials. In the 1980s, developed countries such as the United States and Japan added a certain amount of rare earth oxides such as lanthanum, yttrium,europium, and erbium to barium oxide and copper oxide compounds, which were mixed, pressed, and sintered to form superconducting ceramic materials, making the widespread application of superconducting technology, especially in military applications, more extensive.

7.1 Superconducting integrated circuits

In recent years, research on the application of superconducting technology in electronic computers has been carried out abroad, and superconducting integrated circuits have been developed using superconducting ceramic materials. If this type of integrated circuit is used to manufacture superconducting computers, it will not only be small in size, light in weight, and convenient to use, but also have a computing speed 10 to 100 times faster than semiconductor computers, with floating point operations reaching 300 to 1 trillion times per second. Therefore, the US military predicts that once superconducting computers are introduced, they will become a "multiplier" for the combat effectiveness of the C1 system in the military.

7.2 Superconducting magnetic exploration technology

Magnetic sensitive components made of superconducting ceramic materials have a small volume, making it easy to achieve integration and array. They can form multi-channel and multi parameter detection systems, greatly increasing the unit information capacity and greatly improving the detection distance and accuracy of the magnetic detector. The use of superconducting magnetometers can not only detect moving targets such as tanks, vehicles, and submarines, but also measure their size, leading to significant changes in tactics and technologies such as anti tank and anti submarine warfare.

It is reported that the US Navy has decided to develop a remote sensing satellite using this rare earth superconducting material to demonstrate and improve traditional remote sensing technology. This satellite called the Naval Earth Image Observatory was launched in 2000.

8.Application of Rare Earth Giant Magnetostrictive Materials in Modern Military Technology

Rare earth giant magnetostrictive materials are a new type of functional material newly developed in the late 1980s abroad. Mainly referring to rare earth iron compounds. This type of material has a much larger magnetostrictive value than iron, nickel, and other materials, and its magnetostrictive coefficient is about 102-103 times higher than that of general magnetostrictive materials, so it is called large or giant magnetostrictive materials. Among all commercial materials, rare earth giant magnetostrictive materials have the highest strain value and energy under physical action. Especially with the successful development of Terfenol-D magnetostrictive alloy, a new era of magnetostrictive materials has been opened up. When Terfenol-D is placed in a magnetic field, its size variation is greater than that of ordinary magnetic materials, which enables some precision mechanical movements to be achieved. At present, it is widely used in various fields, from fuel systems, liquid valve control, micro positioning to mechanical actuators for space telescopes and aircraft wing regulators. The development of Terfenol-D material technology has made breakthrough progress in electromechanical conversion technology. And it has played an important role in the development of cutting-edge technology, military technology, and the modernization of traditional industries. The application of rare earth magnetostrictive materials in modern military mainly includes the following aspects:

8.1 Sonar

The general emission frequency of sonar is above 2 kHz, but low-frequency sonar below this frequency has its special advantages: the lower the frequency, the smaller the attenuation, the farther the sound wave propagates, and the less affected the underwater echo shielding. Sonars made of Terfenol-D material can meet the requirements of high power, small volume, and low frequency, so they have developed rapidly.

8.2 Electrical mechanical transducers

Mainly used for small controlled action devices - actuators. Including control accuracy reaching the nanometer level, as well as servo pumps, fuel injection systems, brakes, etc. Used for military cars, military aircraft and spacecraft, military robots, etc.

8.3 Sensors and electronic devices

Such as pocket magnetometers, sensors for detecting displacement, force, and acceleration, and tunable surface acoustic wave devices. The latter is used for phase sensors in mines, sonar, and storage components in computers.

9. Other materials

Other materials such as rare earth luminescent materials, rare earth hydrogen storage materials, rare earth giant magnetoresistive materials, rare earth magnetic refrigeration materials, and rare earth magneto-optical storage materials have all been successfully applied in modern military, greatly improving the combat effectiveness of modern weapons. For example, rare earth luminescent materials have been successfully applied to night vision devices. In night vision mirrors, rare earth phosphors convert photons (light energy) into electrons, which are enhanced through millions of small holes in the fiber optic microscope plane, reflecting back and forth from the wall, releasing more electrons. Some rare earth phosphors at the tail end convert electrons back into photons, so the image can be seen with an eyepiece. This process is similar to that of a television screen, where rare earth fluorescent powder emits a certain color image onto the screen. The American industry typically uses niobium pentoxide, but for night vision systems to succeed, the rare earth element lanthanum is a crucial component. In the Gulf War, multinational forces used these night vision goggles to observe the targets of the Iraqi army time and time again, in exchange for a small victory.

10 .Conclusion

The development of the rare earth industry has effectively promoted the comprehensive progress of modern military technology, and the improvement of military technology has also driven the prosperous development of the rare earth industry. I believe that with the rapid advancement of world science and technology, rare earth products will play a greater role in the development of modern military technology with their special functions, and bring huge economic and outstanding social benefits to the rare earth industry itself.