There are 17 elements in total, known as rare earth elements, including lanthanum (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) and scandium (Sc) and yttrium (Y), which are closely related to 15 elements in the lanthanide series.
Rare earth elements are a group of 17 special elements that get their name from the compounds that scientists use to extract them.
Rare earth elements classification
Generally, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium are called light rare earth elements, and gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium are called heavy rare earth elements. According to the similarities and differences in the physical and chemical properties of rare earth elements, in addition to scandium (scandium is classified as scattered elements) can be divided into three groups, that is, the light rare earth group is lanthanum, cerium, praseodymium, neodymium and promethium, of which promethium is artificial radioactive element. The middle-rare earth group is samarium, europium, gadolinium, terbium and dysprosium. The heavy rare earth groups are holmium, erbium, thulium, ytterbium, lutetium and yttrium.
Rare earth elements are very active metals with very similar properties. The common valence is +3. Most of the hydrated ions have color and are easy to form stable coordination compounds. Solvent extraction and ion exchange are the best methods for rare earth separation. Light rare earth metals such as lanthanum, cerium, praseodymium and neodymium are generally obtained by electrolysis because of their low melting point and precipitation on the cathode in a molten state during electrolysis. Two salt systems are available: chloride and fluoride. The former is added to the electrolytic cell with rare earth chloride as raw material, while the latter is added in the form of oxide.
Rare earth elements types and applications
1. Light rare earth group elements
Lanthanum is widely used, such as used in piezoelectric materials, electrothermal materials, thermoelectric materials, magnetic resistance materials, luminescent materials (blue powder), hydrogen storage materials, optical glass, laser materials, all kinds of alloy materials. Lanthanum is also used in the preparation of many organic chemical products in the catalyst, light conversion agricultural film is also used in lanthanum, in foreign countries, scientists to the role of lanthanum on crops and “super calcium” laudable name.
(1) Cerium is currently being used in catalysts for purifying automobile exhaust, which can effectively prevent a large amount of automobile exhaust from being discharged into the air. The CONSUMPTION of rare earth in this area in the United States accounts for one third of the total consumption.
(2) Ce:LiSAF laser system is a solid state laser developed by the United States. It can be used to detect biological weapons by monitoring the concentration of tryptophan, and can also be used in medicine.
Praseodymium is a large amount of rare earth elements, used in glass, ceramics and magnetic materials.
(1) Praseodymium is widely used in architectural ceramics and daily ceramics. It is mixed with ceramic glaze to make color glaze, and can also be used separately as underglaze pigment. The pigment made is light yellow with pure and elegant tone.
(2) Used to manufacture permanent magnets. Using cheap praseodymium and neodymium metal instead of pure neodymium metal to manufacture permanent magnetic materials, its antioxidant and mechanical properties are obviously improved, can be processed into various shapes of magnets, widely used in various electronic devices and motors;
(3) for petroleum catalytic cracking. The activity, selectivity and stability of petroleum cracking catalyst prepared by adding enrichment of praseodymium and neodymium into Y zeolite molecular sieve can be improved. China began to put into industrial use in the 1970s, the amount of increasing;
(4) Praseodymium can also be used for abrasive polishing. Praseodymium is also widely used in optical fiber.
Neodymium has been the focus of the market for many years because of its unique position in the field of rare earth.
(1) The largest user of neodymium metal is ndfeb permanent magnet material. The advent of NdFEB permanent magnet has injected new vigor and vitality into the high-tech field of rare earth. Ndfeb magnet with high magnetic energy product, known as the contemporary “king of permanent magnet”, is widely used in electronics, machinery and other industries with its excellent performance. The success of the development of alpha magnetic spectrometer, marking the magnetic properties of Ndfeb magnets in China has entered the world first-class level.
(2) Neodymium is also used in non-ferrous metal materials. Adding 1.5% ~ 2.5% neodymium to magnesium or aluminum alloy can improve the alloy’s high temperature performance, air tightness and corrosion resistance, and is widely used as aerospace materials. In addition, neodymium-doped yttrium aluminum garnet produces short-wave laser beams and is widely used in industry for welding and cutting of thin materials with thickness below 10mm.
Promethium is a man-made radioactive element produced by nuclear reactors. Its main uses are:
(1) It can be used as a heat source to provide auxiliary energy for vacuum detection and artificial satellites.
(2) Pm147 emits low energy β ray, used for manufacturing promethium battery, as the power supply of missile guidance instruments and clocks. This kind of battery is small in size and can last for several years. Promethium is also used in portable X-ray meters, phosphors, thickness measurements, and beacon lights.
2. Medium rare earth group elements
Samarium, which is light yellow in color, is the raw material for samarium cobalt permanent magnets, which are the earliest rare earth magnets for industrial use. There are two kinds of permanent magnets: SmCo5 and Sm2Co17.
The purity of samarium oxide used in samarium cobalt magnets does not need to be too high. In terms of cost, about 95% of the product is mainly used. Samarium oxide is also used in ceramic capacitors and catalysts. In addition, samarium also has nuclear properties, which can be used as structural material, containment material and control material for atomic reactors, so that the huge energy generated by nuclear fission can be safely utilized.
Europium oxide is mostly used in phosphors. Eu3+ is used as an activator for red phosphors and Eu2+ for blue phosphors. Now Y2OS:Eu3+ is the best phosphor for luminescence efficiency, coating stability and cost recovery, coupled with the improvement of luminescence efficiency and contrast and other technologies, so it is widely used.
Gadolinium is mainly used for:
(1) Its water-soluble paramagnetic complex can improve human nuclear magnetic resonance (NMR) imaging signal in medical treatment.
(2) Its sulfur oxide can be used as the matrix grid of oscilloscope tube and X-ray screen with special brightness.
(3) Gadolinium in gadolinium gallium garnet is an ideal single substrate for magnetic bubble memory.
Most applications of TERbium involve high-tech fields, which are technology-intensive and knowledge-intensive cutting-edge projects. The main applications include:
(1) phosphor green powder activator for three color phosphor, such as terbium activated phosphate matrix, silicate matrix, cerium magnesium aluminate matrix, in the excitation state of green light.
(2) magneto-optical storage materials, in recent years, terbium series magneto-optical materials have reached the scale of mass production, with TB-Fe amorphous film developed magneto-optical disc, as computer storage components, storage capacity increased 10 ~ 15 times.
(3) Magneto-optic glass, Faraday rotatory glass containing terbium is a key material in the manufacture of rotators, isolators and circulators widely used in laser technology.
Dysprosium’s main uses are:
(1) Used as additives for Ndfeb permanent magnets, adding about 2%~3% dysprosium to this magnet can improve its coercivity. Dysprosium used to be in small demand, but with the growing demand for Ndfeb magnets, it became a necessary addition.
(2) Dysprosium as a phosphor activator, dysprosium trivalent is a promising activation ion of single-luminescent center three-color phosphor materials, which is mainly composed of two emission bands, one is yellow emission, the other is blue emission, dysprosium doped phosphor materials can be used as three-color phosphor.
(3) Dysprosium is the preparation of large magnetostrictive terbium dysprosium iron (Terfenol) alloy necessary metal raw materials, can make some mechanical movement of precision activities can be realized.
(4) Dysprosium metal can be used as magneto-optical storage materials, with high recording speed and reading sensitivity.
3. Heavy rare earth group elements
The main uses of holmium currently are:
(1) Used as additive for metal halogen lamp. Metal halogen lamp is a kind of gas discharge lamp, it is based on high pressure mercury lamp developed, its characteristic is filled with various rare earth halides in the bulb.
(2) Holmium can be used as an additive for yttrium iron or yttrium aluminum garnet.
(3) Yttrium aluminum garnet doped with holmium (Ho:YAG) can emit 2μm laser, and the absorption rate of 2μm laser in human tissues is high, almost 3 orders of magnitude higher than Hd:YAG. So when Ho:YAG laser is used in medical surgery, not only the efficiency and precision of surgery can be improved, but also the thermal damage area can be reduced to smaller.
Erbium has been the focus of attention because of its outstanding optical properties:
(1) Er3+ emission at 1550nm is of special significance, because this wavelength is located at the lowest loss of optical fiber in optical fiber communication. Er3+ transitions from ground state 4I15/2 to high energy state 4I13/2 after being excited by light at wavelength 980nm and 1480nm. When Er3+ in the high energy state transitions back to the ground state and emits light of 1550nm wavelength, the quartz fiber can transmit light of different wavelengths, but the optical decay rate of different light is different. The optical attenuation rate of 1550nm frequency band in the quartz fiber is the lowest (0.15dB/km), which is almost the lower limit attenuation rate.
(2) the other erbium laser crystal and its output of 1730 nm and 1550 nm laser is safe for people eyes, atmospheric transmission performance is good, the smoke of the battlefield penetration ability is stronger, the secrecy good, not easy detection by enemy, illuminate large quantities of military targets, has made it safe for military use portable laser range finder.
(3) When Er3+ is added to glass, it can be made into rare earth glass laser material, which is the solid laser material with the largest pulse energy and highest output power at present.
Thulium is mainly used in the following ways:
(1) Thulium is used as a radiation source for portable medical X-ray machines. After being irradiated in nuclear reactors, thulium produces an isotope capable of emitting X-rays, which can be used to manufacture portable blood irradiators.
(2) Thulium can also be used in clinical diagnosis and treatment of tumors, because it has a high affinity for tumor tissue, heavy rare earth is more than light rare earth affinity, especially thulium has the highest affinity.
(3) Thulium can be used as activator lao-Br :Br (blue) in fluorescent powder used in X-ray sensitization screen to enhance optical sensitivity, thus reducing the exposure and harm of X-ray to human. Compared with previous calcium tungstate sensitization screen, the X-ray dose can be reduced by 50%, which is of great significance in medical application.
The main uses of ytterbium are:
(1) as heat shielding coating material.
(2) as magnetostrictive materials, this material has the property of giant magnetostriction, that is, expansion in a magnetic field.
(3) Ytterbium element used for pressure measurement. The test proves that the ytterbium element has high sensitivity in the calibrated pressure range, which opens a new way for the application of ytterbium in pressure measurement.
The main uses of lutetium are:
(1) Manufacture of some special alloys such as lutetium aluminum alloy can be used for neutron activation analysis.
(2) Stable lutetium nuclides catalyze petroleum cracking, alkylation, hydrogenation and polymerization.
(3) as addition element of yttrium iron or yttrium aluminum garnet to improve some properties.
Yttrium is a metal with a wide range of uses, including:
(1) additives for iron and steel and nonferrous alloys.
(2) Silicon nitride ceramic materials containing yttrium 6% and aluminum 2%, which can be used to develop engine components;
(3) with the power of 400W nd yttrium aluminum garnet laser beam can be used for drilling, cutting, welding and other mechanical processing of large components.
4. Scattered elements
(1) Lighting industry. Interestingly, the use of scandium (as the main working substance, not for doping) is concentrated in the direction of the light, and it is fair to call it the son of light. Such as scandium sodium lamp, solar cell, γ ray source, etc.
(2) Scandium in its elemental form has been widely used in aluminum alloy doping.
(3) Scandium in its elemental form is generally used in alloys, and the oxide of scandium also plays an important role in ceramic materials. Image can be used as solid oxide fuel cell electrode material, but also can be used as high strength, high temperature resistant engineering ceramic material silicon nitride as a densifier and stabilizer.
(4) Adding a small amount of Sc2O3 into the nuclear fuel of the high temperature reactor can avoid the lattice transformation, volume increase and crack caused by the conversion of UO2 to U3O8.
Rare earth elements have been widely used in electronics, petrochemical, metallurgy, machinery, energy, light industry, environmental protection, agriculture and other fields.
Post time: Aug-20-2022