Rare earth elements are a collective term for 17 special elements, including lanthanide elements in the periodic table of chemical elements - lanthanide (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), as well as 15 closely related elements of the lanthanide system - yttrium (Y) and scandium There are 17 elements in Sc, called rare earth elements. Rare earths are important strategic resources, known as "industrial vitamins", and have been widely used in fields such as electronics, petrochemical, metallurgy, machinery, energy, light industry, environmental protection, agriculture, etc. Today, let's first introduce the first ranked metal lanthanum.
1、 Introduction to Lanthanum
In 1839, Swedish chemist Carl Mosander discovered "lanthanum" (named after the Greek word for "hidden"). Lanthanum is a metallic rare earth element with atomic number 57 and atomic weight of 138.9055. Silver gray luster, soft texture, density 6.174g/cm ³， Melting point 921 ℃, boiling point 3457 ℃; The content of lanthanum in the crust is 0.00183%, second only to cerium in rare earth elements. Lanthanum has two natural isotopes: lanthanum 139 and radioactive lanthanum 138.
Lanthanum metal is a silver white metal that is soft and easy to cut. Lanthanum metal has active chemical properties and is easily soluble in dilute acids. It is easy to oxidize in the air, and fresh surfaces quickly darken when exposed to air. Lanthanum metal is generally stored in mineral oil or rare gases. Heating can burn, producing oxides and nitrides. Heating in hydrogen gas generates hydrides, which react strongly in hot water and release hydrogen gas. Lanthanum exists in monazite sand and bastnaesite. The element of lanthanum is a malleable, malleable silver white metal, which can be cut with a knife if it is soft; Melting point 921 ° C, boiling point 3457 ° C, density 6.174 grams/cubic centimeter. Lanthanum has active chemical properties and slowly corrodes in cold water, accelerating in hot water; Lanthanum can directly react with carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, halogens, etc; Lanthanum compounds are diamagnetism.
2、 Application of Lanthanum Metal
（1） Steel modifier
Adding lanthanum or mixed rare earth metals to steel can remove sulfur and oxygen, refine grain size, form microalloys, change the morphology and distribution of inclusions, reduce hydrogen diffusion coefficient, and improve resistance to hydrogen embrittlement and stress corrosion; Adding iron can purify molten iron, change graphite morphology, and prevent impurities from damaging spheroidization. Due to the widespread application of steel in various fields, lanthanum metal plays an important role in the development of high-performance products such as steel and cast iron.
（2） Reducing agent
Metal lanthanum and cerium have similar properties. Lanthanum chips are mixed with samarium oxide and compressed into blocks, and reduction reactions occur at high temperatures. High vapor pressure metals such as samarium can be obtained by vacuum distillation and purification using vapor pressure difference; The equipment for this process is a vacuum induction furnace or vacuum resistance furnace, where the reduction and distillation processes are carried out simultaneously, resulting in a simple process and minimal pollution.
（3） Metal square bar lining
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 substances. Therefore, it was made into flint as early as 1908. It has been found that among the 17 rare earth elements, six elements, cerium, lanthanum, neodymium, praseodymium, samarium, and yttrium, have particularly good arson performance. And lanthanum has the lowest price. People have made various incendiary weapons based on the arson properties of rare earth metals. For example, the 227kg American "Mark 82" missile uses rare earth metal liners, which not only produce explosive killing effects but also arson effects. The US air-to-ground "damping man" rocket warhead is equipped with 108 rare earth metal square rods as liners, replacing some prefabricated fragments. Static explosion tests have shown that its ability to ignite aviation fuel is 44% higher than that of unlined ones.
（4） Metal lanthanum wire foil
The metal lanthanum wire can absorb harmful gases such as oxygen, nitrogen, carbon monoxide, carbon dioxide, and water vapor released by the electron tube electrode due to bombardment and thermal diffusion, thereby maintaining the high vacuum of the electron tube. Various rare earth metals and alloy foils have a large neutron absorption area and can effectively capture neutrons. Lanthanum wire and foil are widely used in electronics, lighting, nuclear industry and other fields.
（5） Igniting alloy
In the early days of our country, various ignition alloys were made from mixed rare earth metals (RE, containing La25%) and Fe, and can be divided into military and civilian types. Military ignition alloys are made of RE60-80% (including La25%), Fe20-40%, and a small amount of Al, Ca, Si, and C, mainly used for manufacturing bullets, shells, and bombs, as well as ignition devices. Civil ignition alloys are made of RE75-80% (including La25%), Fe15-18%, and a small amount of Mg, Zn, Cu, Al, etc., with a ignition rate of ≥ 85%. They are mainly used for igniting flints in lighters and various toys. In addition, igniting alloys are also used for industrial steam lamps, welding torch igniters, and torch igniters.
（6） For non-ferrous metals
Metal lanthanum powder has a larger specific surface area, stronger activity, and better dispersibility than metal lanthanum blocks, and its applications in precision alloys, special metals, and catalysts are increasing day by day. Tungsten alloys, molybdenum alloys, and titanium alloys have problems such as low grain boundary strength and low temperature brittleness; During its processing, rare earth metal powders such as lanthanum powder are added and thoroughly mixed, which can utilize the effect of rare earth microalloying to effectively refine the structure, capture harmful elements such as hydrogen, and improve alloy performance.
（7） Metallic lanthanum target
Metal lanthanum targets are mainly used in fields such as coating and polishing. The use of thorium tungsten material as a thermionic cathode poses a radioactive problem, while lanthanum molybdenum cathode does not. Its emission performance largely depends on the surface active material layer of the material. Hao Shiming et al. used molybdenum as the substrate and lanthanum as the target material to prepare uniformly distributed lanthanum oxide thin films using pulse laser technology, and obtained excellent performance lanthanum molybdenum cathodes. CVD diamond film has good thermal conductivity and transparency, and is widely used, but the surface grain size and roughness of the film are large, resulting in low performance. By utilizing the reaction diffusion of carbon elements and rare earth metals on the surface of diamond to achieve surface polishing, the polishing speed can be accelerated and the precision of diamond films can be improved. High purity lanthanum targets have fewer impurities and vacancies, resulting in a more uniform structure and stable performance of the sputtered film layer.
3、 Application of Lanthanum Compounds (1) Lanthanum Oxide (La2O3)
White amorphous powder with a density of 6.51. Melting point 2315 ℃. Boiling point 4200 ℃. Slightly soluble in water, soluble in acids to form corresponding salts. Exposed to the air, it absorbs carbon dioxide and gradually transforms into lanthanum carbonate. It is used for making special alloys, optical glass, etc. Extracted from lanthanum phosphate cerium ore or obtained by burning lanthanum carbonate or nitrate. Manufacturing various alloy materials, such as aluminum alloys for aircraft; Luminous materials, road signs and pavement luminous stones; Optical glass, such as camera and camera lens; Optical fiber; Advanced capacitors; Glass decolorizing agent to increase strength; Laser materials; Pigments and gloss agents for porcelain; Magnetoresistive material; Hydrogen storage materials; Mobile phone battery; Catalysts for organic chemical products, such as light conversion agricultural films.
（2） Lanthanum sulfate (La2 (SO4) 3)
Slightly soluble in cold water, with an increase in temperature and a decrease in solubility, insoluble in acetone. It is the least soluble rare earth metal sulfate. The most common is its octahydrate hydrated lanthanum sulfate, which is a colorless hexagonal crystal. It dehydrates at 500 ℃ and generates basic salts at 700 ℃. It can form various sulfate complex salts with alkali metal sulfates. La (HSO4) 3 is generated in sulfuric acid, and sulfides are generated when heated under the flow of sulfurized hydrogen gas. Hydrated lanthanum sulfate can be used for determining the atomic weight of elements, spectral analysis, and as a preservative and reagent.
8 hydrated lanthanum sulfate
（3） Lanthanum carbonate (La ₂ (CO Å))
Lanthanum carbonate can reduce the blood calcium and phosphorus levels in patients with high calcium and high phosphorus MHD, and is safe. It can be used to treat hyperphosphatemia accompanying dialysis in kidney disease patients.
Lanthanum carbonate, as a new type of phosphorus binder that does not contain aluminum or calcium, is gradually being used in the clinical treatment of hyperphosphatemia. Lanthanum carbonate has good phosphorus binding capacity in acidic environment. The trivalent lanthanum ion is highly compatible with phosphorus in gastric acid environment, can closely bind phosphorus in food, form insoluble and digestible lanthanum phosphate, and excrete with feces, which can play a role in reducing the blood phosphorus level, and there is no side effect caused by increased aluminum and calcium intake.
（4） Lanthanum hexaborate (LaB6)
It is an excellent electron emission material with high melting point (>2500 ℃), low vapor pressure, and low work function. Its electron emission performance is better than tungsten, and it has been widely used as an electron gun in electron microscopes, televisions, and cathode ray tubes.
LaB6 is an excellent cathode material with low work function, especially suitable for devices with high temperature and high current density. Based on its unique structure, it has excellent electronic activity. During heating, the metal La atoms diffused from the crystal cell can immediately supplement the metal La atoms evaporated from the surface, maintaining good cathodic activity on the LaB6 surface. Due to its high conductivity, good thermal stability, chemical stability, low work function and excellent cathode surface activity, LaB6 is widely used in cathode emission and becomes a good hot cathode material and field emission cathode material.
Crystal Structure Model of LaB6
（5） Lanthanum bromide oxide (LaBrO)
It has a strong absorption characteristic for X-ray and can effectively convert X-ray into visible light. It is used to make medical X-ray intensifying screen, which greatly improves the imaging clarity compared with the traditional Calcium tungstate (CaWO4) intensifying screen, and reduces the radiation dose of X-ray. It is especially suitable for fluoroscopy of brain sensitive parts and children and pregnant women
（6） Lanthanum bromide (LaBr3)
Light gray white powder, easy to absorb moisture; Density (25/4 ℃) 5.063g/mL; Melting point 7834 ℃; Boiling point 15775 ℃; Soluble. Cerium doped lanthanum bromide single crystal (LaBr3: Ce3+) is an excellent scintillator material with superior scintillation performance compared to sodium iodide, cerium doped lanthanum chloride, etc.
Lanthanum bromide LaBr3 (ce) scintillation crystal is the main component of the nuclear radiation probe. The scintillation probe can be used to detect X-rays and γ Ionizing radiation such as radiation. Lanthanum cerium bromide scintillation crystal has the advantages of high light yield, good energy resolution, short attenuation time, small nonlinear response, etc. It can be widely used in international anti-terrorism and anti-terrorism, nuclear material control, safety inspection, energy, nuclear medicine, industrial metrology, oil logging and other fields.
LaBr3 (ce) crystal of lanthanum bromide
（7） Lanthanum nitrate (La (NO3) 3)
White granular crystals, easy to wet dissolve; Boiling point 126 ℃; Melting point 40 ℃; Solubility: easily soluble in water, easily soluble in ethanol; Density: relative density (water=1) 2.05; Stability: Stable; Hazard sign 11); Main applications: used to make optical glass, fluorescent powder, ceramic capacitor additive, and petroleum refining catalyst
1. It is used to produce optical glass, vapour lamp gauze cover, phosphor and preservative.
2. Ceramic capacitor additives and petroleum refining catalysts.
6 hydrated lanthanum nitrate
（8） Lanthanum chromate (LaCrO3)
Lanthanum chromate material is a composite oxide with a cubic perovskite structure at high temperatures (>1000 ℃), a theoretical density of 6.5g/cm3, and a melting point of 2490 ℃. Pure lanthanum chromate is an intrinsic intrinsic semiconductor, which can become a p-type semiconductor with good conductivity after appropriate doping. Due to the presence of oxygen in the chemical formula, the lanthanum chromate electric heating element prepared by using lanthanum chromate material as the substrate and adding other materials has good high-temperature oxidation resistance. The surface temperature can reach 1900 ℃ in an air environment, and the long-term stable working temperature in the furnace can reach 1700 ℃. Resistance heating elements used in high-temperature oxidation atmosphere electric furnaces; It consumes less energy and can accurately control temperature. It can be used for a long time in an oxidizing atmosphere and is suitable for high-precision automatic temperature control. Its furnace temperature stability can be within 1 ℃.
（9） Lanthanum silicate (La3Ga5SiO14)
It is an ideal material for producing high stability, high frequency, large bandwidth, low insertion loss, and small volume SAW filters. The Caqin type manganese based oxide La-Ca-Mn-O material has the Giant Magneto Resistance effect (CMR), which has promoted the development of a new discipline spintronics, and has begun to be applied in many new electronic devices.
Gallium lanthanum silicate (LGS) crystal
Gallium lanthanum silicate (LGS) crystals, like quartz crystals, belong to the tripartite crystal system, but their electromechanical coupling coefficient is 2-3 times higher than that of quartz crystals. They are non deliquescent, insoluble in acids and bases, have zero temperature coefficient tangential, low SAW propagation rate, no phase transition, and do not require polarization treatment. They are excellent piezoelectric crystal materials. However, due to the fact that half of its components weigh Ga2O3, the high cost makes it difficult to compete with large and affordable quartz crystals. Therefore, devices made of LGS crystals are only used in a few areas that require excellent properties regardless of cost, such as aviation, aerospace, or military.
In recent years, due to the development of mobile communication, small intermediate frequency acoustic bulk wave filters made by LGS have been used in broadband wavelength division multiplexing (W-CDMA) systems and have once again received attention.
4、 The application range of lanthanum alloys
（1） Nuclear radiation shielding
Application principle: 1% boron and 5% rare earth elements gadolinium, samarium and lanthanum are used to make 600mm thick radiation proof concrete for shielding the fission neutron source of swimming pool reactor.
France developed a rare earth radiation protection material by adding boride, rare earth compound or rare earth alloy to graphite as the base material. 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 area.
（2） Hydrogen storage materials
Energy is the basis for the development of national economy and science and technology. The development and utilization of green and efficient hydrogen energy can effectively alleviate the energy crisis, and the storage and transportation of hydrogen energy is the key technology. Metal alloy solid hydrogen storage has the advantages of high energy density, safety and environmental protection. The LaNi5 alloy discovered in 1970 is an excellent hydrogen storage material that can store approximately 160 liters of hydrogen per kilogram, reducing the volume of high-pressure hydrogen storage cylinders to 1/4. By utilizing its ability to "breathe" hydrogen gas, hydrogen gas with a purity of 99.999% can be purified to 99.9999%, and can also be used as a catalyst for hydrogenation or dehydrogenation reactions in organic synthesis. By utilizing its ability to absorb hydrogen, release heat, and exhale hydrogen, heat can be transferred from low to high temperatures, and used to make "heat pumps" or "magnetic refrigerators". Yan Huizhong et al. studied the structure, hydrogen storage performance, electrochemical performance, treatment process, and application of lanthanum containing binary and multivariate hydrogen storage alloys, focusing on how to improve the hydrogen storage capacity of materials. Currently, the industrialization technology is relatively mature. Research has shown that the purity of raw materials affects the microstructure of materials, and high-purity raw materials can effectively improve the hydrogen storage capacity and service life of hydrogen storage alloys.
At present, the biggest use of this hydrogen storage material is as a negative electrode material for rare earth nickel hydrogen batteries. Rare earth nickel hydrogen batteries have great similarities and substitutability with nickel cadmium batteries in terms of structure, performance, and specifications, but they do not contain toxic elements such as cadmium and mercury. The batteries have high capacity, good consistency, wide temperature range, long lifespan, and can be recharged and discharged more than 500 times, making them environmentally friendly and green batteries. In order to reduce costs, this hydrogen storage alloy often uses lanthanum rich mixed metals with La ≥ 40% as raw materials. Rare earth nickel hydrogen batteries are currently widely used in portable computers, office equipment, and power tools. The most promising development is the power battery used in automobiles and motorcycles.
A material used as an anode material for nickel hydrogen batteries is La (Ni3.6Mn0.4Al0.3Co0.7). Due to the high cost of extracting other lanthanide elements, mixed rare earths containing over 50% lanthanum are used instead of pure lanthanum. This compound is an AB5 type intermetallic compound.
（3） Magnetic cooling material
Magnetic refrigeration refers to a new refrigeration technology using magnetic materials as the medium. Its basic principle is to use the magnetocaloric effect of magnetic cooling materials (i.e., the magnetic cooling material releases heat to the outside world during isothermal magnetization, and absorbs heat from the outside world during adiabatic demagnetization) to achieve the purpose of refrigeration. The magnetic cooling medium must have a giant magnetic entropy change. La-Fe series compounds have a NaZn13 structure, and there is a giant magnetic entropy change within the phase transition temperature range. Adding an appropriate amount of other elements to La-Fe series compounds can effectively increase their Curie temperature and achieve excellent magnetic cooling effects. They are currently the most promising room temperature magnetic cooling materials for practical use, but their binary alloys are unstable. The research focus at home and abroad is on the preparation process of this series of alloys.
（4） Shielding coating
Electromagnetic radiation is an important source of pollution in the information society, and shielding is one of the most effective methods to resist electromagnetic interference. Lanthanide based electromagnetic shielding coatings have high shielding efficiency for electromagnetic waves, but their impedance is higher than that of silver series. Adding rare earths can adjust their electromagnetic parameters, reduce impedance, and improve shielding performance. Adding lanthanum to the lanthanide based electromagnetic shielding coating to prepare Cu La based coating improved the conductivity and electromagnetic shielding performance of the coating. Its electromagnetic shielding effectiveness reached 89dB for electromagnetic waves ranging from 30MHz to 1.5GHz, indicating good shielding effectiveness.