What magical uses do rare earth elements have? (Ⅲ) ——About the application of light rare earth elements

There are 17 rare earth elements, which are divided into ‘light rare earth’ and ‘heavy rare earth’ according to atomic number and atomic mass: Among them, Light rare earth elements have lower atomic number, smaller atomic mass, and great storage, including lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium;

Heavy rare earth elements have higher atomic number, larger atomic mass, and lower reserves, including gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.

According to the rare earth element acid extraction separation process, rare earth elements are divided into :

Light rare earth (weak acid extraction) - lanthanum, cerium, praseodymium, neodymium;

Intermediate rare earth (low acid extraction) – samarium, europium, gadolinium, terbium, and dysprosium;

Heavy rare earths (medium acid extraction) - holmium, europium, erbium, thulium, ytterbium, lutetium, yttrium.

Generally speaking, light rare earths are widely used in metallurgy, ceramics, the chemical industry, electronics, medical treatment, superconductivity, and other fields; heavy rare earth are widely used in phosphors, optical glass, laser crystals, electric light sources, ceramic glazes, printing and dyeing industry, catalysts, etc.

The following is an introduction to the applications of individual rare earth elements.

1. Application of lanthanum (lǎng in Chinese)

Lanthanum, element symbol La is pronounced lǎng in Chinese. Atomic weight is 138.9055.

Lanthanum can be made into high-grade optical glass. Adding lanthanum oxide to optical glass can significantly ‘increase the refractive index’ and ‘reduce the dispersion rate’. The optical instrument lens made in this way can expand the viewing angle, reduce image distortion, and improve resolution. Lanthanum is also indispensable in today's laser materials.

Lanthanum is the best in electronic communication materials. Currently, the best electron emission material is LaB6, and lanthanum has excellent applications in many electronic communication materials. Lanthanum plays an excellent role in functional ceramics. For example, adding ‘lanthanum oxide’ to barium titanate (BaTiO3) capacitor ceramics can significantly improve the stability of the capacitor and increase its service life by hundreds of times. For example, adding lanthanum oxide to ‘radiation-proof ceramics’ and ‘electro-optical ceramics’ can greatly improve performance.

Lanthanum is an excellent catalyst in petrochemicals. The ‘cracking’ and ‘polymerization’ technologies of molecules are very common in petrochemicals, but catalysts are indispensable. Adding rare earth elements ‘scandium’ and ‘lanthanum-rich rare earth’ to the catalyst doubles the cracking efficiency. If then the catalyst is made into a ‘molecular sieve catalyst’ with ‘good permeability’ and ‘large contact area’, the catalytic effect will be doubled.

Lanthanum nickel alloy (LaNi5) is an excellent hydrogen storage material. Hydrogen storage materials help with ‘hydrogen storage’, ‘hydrogen transportation’ and ‘hydrogen use’, but purify the hydrogen from hydrogen mixtures.

2. Application of Cerium

Cerium, element symbol Ce, pronounced shì in Chinese. Atomic weight is 140.1.

Cerium, as a glass additive, can absorb ultraviolet and infrared rays, which is now widely used in automobile glass. It is more effective not only to prevent ultraviolet rays but also to reduce the temperature inside the car, thereby saving electricity for air conditioning.

Cerium is used in automobile exhaust purification catalysts, which can effectively prevent automobile exhaust pollution.

Cerium sulfide performs outstandingly in pigments and dyes. Cerium replaces the previous toxic materials, such as lead and cadmium, and has a good performance in pigments and dyes. It is now widely used in the coloring of plastics, inks, and paper, and is also widely used in the field of coatings.

The application field of cerium is very wide, and almost all rare earth application fields contain cerium, such as rare earth polishing and grinding materials, rare earth hydrogen storage materials, rare earth optical glass materials, rare earth thermoelectric materials, rare earth cracking agents, electrode materials, rare earth ceramic materials, rare earth magnetic materials, rare earth alloy steel materials, etc.

3. Application of praseodymium

Praseodymium, element symbol Pr, is pronounced pǔ in Chinese. Atomic weight is 140.90765.

Praseodymium is generally used in ‘mixed light rare earth’ and is widely used in polishing materials, grinding materials, hydrogen storage materials, optical glass materials, thermoelectric materials, electrode materials, special ceramic materials, cracking agent materials, permanent magnetic materials, and alloy steel materials, etc.

It is worth mentioning that praseodymium is used alone in ‘ceramic glazes’, and the color after firing is pure and elegant light yellow; therefore, it can also be used in ceramic glazes, pigments, dyes, coatings, etc. Of course, other rare earth elements will also have different sintering colors.

4. Application of Neodymium

Neodymium, element symbol Nd, is pronounced nǚ in Chinese. Atomic weight is 144.2.

Neodymium is mostly used in NdFeB permanent magnet materials. NdFeB permanent magnets are known as the contemporary ‘king of permanent magnets’, and their excellent permanent magnetic properties are widely used in electronics, machinery, and other industries. If ‘light rare earth’ replaces neodymium, its permanent magnetic effect is not much different, but the cost is greatly reduced.

Neodymium is also used in non-ferrous metal materials. Adding 1.5 to 2.5% neodymium to magnesium or aluminum alloys can improve the high-temperature performance, air tightness, and corrosion resistance of the alloy. Such materials are widely used as aerospace materials.

Neodymium-doped yttrium aluminum garnet produces short-wave laser beams, which are widely used in industry for welding and cutting of thin materials with a thickness of less than 10 mm. After improved, this laser is able to be used in the medical field.

Neodymium is also used for coloring glass and ceramic materials and as an additive for rubber products.

5. Application of Promethium

The symbol of Promethium is Pm, pronounced as pǒ in Chinese. Atomic weight is 147.

The main application area of Promethium is radioluminescence. Since Promethium is a product of the spontaneous fission of uranium and has a hexagonal unit cell, its physical and chemical properties are similar to those of Neodymium and Ruthenium.

Twenty-eight Promethium isotopes have been discovered, among which Promethium-147 can emit low-energy β-rays, used to make pill-sized atomic batteries with a service life of 5 years. It can be used in artificial satellites, hearing aids, and various military and civilian instruments and meters.

Since Promethium-147 can emit low-energy β-rays, and zinc sulfide will emit cold light under the action of rays, the two substances can be mixed to make ‘radioluminescent powder’ for night observation of instruments and meters, and can also be made into ‘night-shining pearls’.

Similarly, the low-energy radioactive source of Promethium-147 can be converted into a heat source to provide auxiliary energy for vacuum detection, artificial satellites, etc.

6. Application of Samarium

Samarium, element symbol Sm, is pronounced as shān in Chinese. Atomic weight is 150.36.

Samarium is light yellow, and its atoms have the characteristics of ‘large magnetic moment’ and ‘large absorption energy’.

The first and second-generation permanent magnets are inseparable from samarium cobalt, and the third-generation permanent magnets are ‘neodymium iron boron’. It is now found that ‘samarium iron nitrogen’ permanent magnets are of low cost, better high-temperature resistance and corrosion resistance.

Samarium-doped calcium fluoride can output pulsed lasers, and samarium oxide and samarium fluoride can be made into laser ‘filter films’. Samarium doped in ‘garnet’ crystals can be made into infrared filters.

Samarium gadolinium-enriched products can be made into high-performance ‘insulating ceramics’.

Samarium oxide can polymerize methane into ethane and ethylene; samarium diiodide can reduce acetaldehyde to ethanol.

Samarium has strong absorption energy for neutrons and can be used as a neutron absorber in nuclear reactors. After irradiation, samarium turns into ‘samarium isotope’, which can emit low-energy beta rays and gamma rays, and can be used in ‘local radiotherapy’ and ‘image tracking’ in medicine.

7. Application of Europium

Europium, element symbol Eu, is pronounced yǒu in Chinese, and its atomic weight is 151.964.

The biggest feature of europium is that its electronic 'energy level' is easily excited, and the electrons will jump from the 'low energy level' to the 'high energy level'. And when the electrons return from the 'high energy level' to the 'low energy level', they will emit light. Of course, the frequency of light emitted by atoms of different substances is also different. Now, the 'rare earth tri-color fluorescent lamp' and 'rare earth halide lamp' doped with europium have replaced the previous 'high-pressure mercury lamp'.

Yttrium oxide doped with (europium) presents a very bright and perfect red spectrum; materials doped with (europium) present a very bright and perfect blue spectrum; doped materials present a very bright and perfect green spectrum. Currently, the color source of the color display screen of TV sets and flat-screen TVs now mostly uses this type of material to make 'excitation phosphors' to form 'color units', and then uses different intensities of electronic excitation to display various colors.

Doping europium oxide can be used to make colored lenses and optical filters. The reason why it can filter out light of a certain frequency is that it either blocks the passage of light of a certain frequency or converts light of a certain frequency into light of other frequencies.

Doping europium into luminescent materials can appropriately convert the frequency of light; converting infrared light into visible light can improve the luminous efficiency and can also be used for ‘night vision’; if visible light is converted into infrared light, it can be used for infrared identification; if the frequency of light is appropriately converted, the conversion efficiency of solar cells can also be improved. If the research and development in this area are further deepened, the applications related are promising.

Europium is widely associated with ‘light-emitting devices’ and ‘light-frequency conversion devices’.

8. Application of Gadolinium

Gadolinium, element symbol Gd, is pronounced gá in Chinese. Its atomic weight is 157.25.

Gadolinium used in alloys, the alloys containing gadolinium have antioxidant properties at higher temperatures.

Gadolinium used in thermal insulation ceramics, thermal insulation ceramics doped with gadolinium oxide have excellent performance and are often used as thermal insulation materials in aviation, automobile, and other industries. Gadolinium oxide can also be used in other materials to improve heat resistance.

It is also used in permanent magnetic materials. As we all know, samarium and lanthanum can both participate in permanent magnetic materials, and permanent magnets doped with gadolinium have higher heat resistance.

As for optical glass, optical glass doped with gadolinium oxide has a high refractive index, low dispersion, and good high-temperature resistance, and is often used in advanced optical lenses. Similarly, this high-performance optical material can improve the performance of ordinary lenses through the method of ‘vapor coating’.

Used in ‘luminescent phosphors’, gadolinium added while doping europium helps the luminescent phosphors to achieve excellent performances, which are used in advanced displays.

For microwave applications, gadolinium is used to make gadolinium yttrium garnet (Gd: Y3Al5O12), which is a gadolinium alloy for microwave equipment. This gadolinium alloy is made by mixing and melting two or more metal elements, and the product of the mixture will have different properties from the previous various metal forms. Gadolinium yttrium garnet is used in microwave equipment and other fields.

And it is also used in ‘magneto-optical effect materials’ and ‘magnetic refrigeration technology’.

Cathode emission materials made by gadolinium and lanthanum yttrium molybdenum together are easy to process, have good emission effects, and stable performance, and can be used in the field of magnetrons.

Adding gadolinium to uranium fuel rods in ‘neutron absorption materials’ can control the nuclear fission rate.

Gadolinium has a strong ability to absorb X-rays and can be used for ‘radiation protection materials’, ‘medical imaging materials’ and other X-ray absorption materials.