High Purity Rare Earth Metals Research Articles

Sublimed fine-grained dysprosium: Significant magnetocaloric effect

As is known, rare-earth metals (REMs) are promising magnetocaloric materials. The magnitude of the magnetocaloric effect (MCE) of REMs significantly depends on their purity. This paper presents results of studies of the magnetic and magnetocaloric properties of sublimed dysprosium, prepared in the course of the present study, with an emphasis on its impurity and structure perfection. The comprehensive analysis of the chemical composition of sublimed dysprosium, which was performed for the first time by atom probe tomography, showed that the metal corresponds to high-purity rare-earth metals (3 N+). The MCE effect was studied using direct measurements of the adiabatic temperature change (ΔTad) in pulsed (up to 50 T) and steady (up to 14 T) magnetic fields. The studies of the MCE of polycrystalline sublimed Dy by direct method showed that the high ΔTad value for sublimed Dy are comparable with those obtained for single-crystal Dy in magnetic fields up to 5 T. The vacuum sublimation, which is more economical and technologically advanced in contrast to single crystal growing, can be used to create magnetocaloric REM-based materials with high MCE values.

Exploration for oxygen diffusion during deoxidation process of terbium with 18O as isotope tracer

Oxygen (O) is the most difficult kind of impurity to be removed from rare earth terbium (Tb), which seriously restricts the promotion of high purity rare earth metal quality. Study the law of oxygen removal during the purification process and clarify the influence and synergism of active substance are of great significance. Herein, isotopic tracer technique (using 18O) has been used to explore the oxygen diffusion process. Secondary ion probe mass spectrometer (SIMS) and Scanning Electron Microscope (SEM) investigated the occurrence state, migration trajectory and relative concentration gradient of oxygen in Tb. The diffusion coefficient as a function of depth and temperature can be simulated based on the experimental data, which is of great significance for the purification and corrosion prevention of Tb. X-ray photoelectron spectroscopy (XPS) clarified the variation of metal valence, indicating the bonding characteristics between O and Tb.

Production and Quality Control of High-Purity Rare-Earth Metal Oxides for Scintillator Crystals of Detecting Medical Systems

Production and Quality Control of High-Purity Rare-Earth Metal Oxides for Scintillator Crystals of Detecting Medical Systems

Production and quality control of high-purity rare-earth metal oxides for scintillator crystals of medical detection systems

The positron emission tomography (PET) detector uses scintillator crystals to provide high image quality. Cerium-activated lutetium orthosilicates are promising crystals for PET detectors. The optical properties of resulting scintillator crystals directly depend on the impurity composition of starting materials, so they are subject to considerably stringent requirements to the basic substance content: Lu 2 O 3 – 99.999 wt.%, CeO 2 – 99.99 wt.%. A starting material used for obtaining lutetium oxide of the required purity was its concentrate with a basic substance content of 99.1 wt.% with REM carbonates containing up to 54 % cerium used to obtain cerium oxide. The paper presents process flow diagrams for obtaining high-purity Lu 2 O 3 and CeO 2 based on a combination of extraction and ion exchange methods. Extraction purification of lutetium and cerium from accompanying rare-earth impurities was carried out using Aliquat 336 and tri- n -butyl phosphate, respectively. Main operating modes of extraction cascades were calculated. The total number of stages was 17 for lutetium purification, and 20 for cerium purification. The purification technology for lutetium and cerium oxides consists in combining purification methods and varying cycles depending on the content of impurities. In this regard, it is necessary to control the quality of resulting substances practically after each stage. The chemical purity of technology products was subjected to analytical control by mass spectrometry with inductively coupled plasma and a spark excitation source.

Magnetic and Electronic Properties of Heavy Lanthanides (Gd, Tb, Dy, Er, Ho, Tm)

Rare earth metals (REM) occupy a special and important place in our lives. This became especially noticeable during the rapid development of industry in the industrial era of the twentieth century. The tendency of development of the rare-earth metals market certainly remains in the XXI century. According to experts estimates the industry demand for chemical compounds based on them will tend to grow during the nearest years until it reaches the market balance. At the same time, the practical use of high-purity rare-earth metals requires the most accurate understanding of the physical properties of metals, especially magnetic ones. Despite a certain decline in interest in the study of high-purity REM single crystals during the last decade, a number of scientific groups (Ames Lab, Lomonosov Moscow State University (MSU), Baikov Institute of Metallurgy and Materials Science Russian Academy of Science (RAS)) are still conducting high-purity studies on high-purity metal samples. The present article is a combination of a review work covering the analysis of the main works devoted to the study of heavy REMs from gadolinium to thulium, as well as original results obtained at MSU. The paper considers the electronic properties of metals in terms of calculating the density of states, analyzes the regularities of the magnetic phase diagrams of metals, gives the original dependences of the Neel temperature and tricritical temperatures for Gd, Tb, Dy, Er, Ho, Tm, and also introduces a phenomenological parameter that would serve as an indicator of the phase transformation in heavy REMs.

Electrochemical Study of Dysprosium in Fused LiCl–KCl Eutectic for Production of High Purity Metal

High purity rare earth metals are essential for research and use as high-performance materials. Even a minute amount of impurities can have significant influence on physical and chemical properties of metals, so some special properties of rare earth materials are exhibited only when they are in the state of high purity. Molten salts are promising reaction media for extractive metallurgy. In particular, molten chlorides are good electrolytes for selective dissolution or deposition of pure reagents; using molten salts provides a promising route for treatment of raw materials. In addition, molten salts proved to be suitable media for metal electrowinning and electrorefining. Available experience in high-temperature electrochemistry allows producing metals in the solid form. One of the advantages of molten salts is their variety. So, it is possible to find a solvent, which chemical and electrochemical characteristics are suitable to carry out a given process.The goal of this work was studying the mechanism of electrochemical reduction of dysprosium ions in molten LiCl–KCl eutectic for production of high purity dysprosium metal.The cathodic reduction of Dy(III) ions was studied on inert molybdenum electrode in the temperature range of 723–843 K under inert atmosphere. Cyclic voltammograms contained one cathodic peak at–3.19±0.11 V and the corresponding anodic peak at –2.95±0.11 V vs. chlorine reference electrode, Fig. The cathodic peak potential was not constant and shifted to the negative values with increasing scan rate. The cathodic peak current was directly proportional to the square root of the polarization rate. It was found that increasing scan rate led to an expected increase of irreversibility of the cathode process. The number of electrons (n) of the electrode reaction for reduction of Dy(III) ions was determined by square-wave voltammetry and the calculated value was equal to 2.93±0.05. According to the theory of linear sweep voltammetry the redox system Dy(III)/Dy(0) is irreversible and controlled by the rate of the charge transfer.So, cathodic reduction of dysprosium ions proceeded in one three-electron electrochemical step at the potential of –3.19 V versus the Cl–/Cl2 reference electrode:DyCl6 3– + 3 e– = Dy + 6 Cl–.Temperature dependence of Dy(III)/Dy couple apparent standard potential was determined by chronopotentiometry at the zero current. The experimental values are described by the linear equation: E*Dy/Dy(III) = –(3.401±0.009) + (6.2±0.1)∙10–4∙T.The apparent standard Gibbs energy change, enthalpy, and entropy of dysprosium trichloride formation from the elements in fused LiCl–KCl eutectic and activity coefficient of DyCl3 were calculated.The influence of different parameters on the composition of the cathode product was investigated. It was found that for fine purification of dysprosium from its impurities, the electrolysis should be carried out in two stages, in which the first stage is the purification electrolysis, and the second one is the base electrolysis.The reported study was funded by Russian Foundation for Basic Research according to the research project No. 20-03-00743.Figure. Typical cyclic voltammograms for the reduction of dysprosium trichloride on molybdenum electrode (S = 0.14 cm2) in fused LiCl–KCl eutectic at 723 K. m(DyCl3) = 4.1∙10–2 mol/kg. Scan rates, V s−1: 1 – 0.075; 2 – 0.2; 3 – 0.5. Figure 1

Research Progress in Preparation and Purification of Rare Earth Metals

The purity of rare earth metals is one of the most important factors to research and develop high technique materials. However, high purity rare earth metals are not easily achieved. This review summarizes the preparation and purification methods of rare earth metals. First, the preparation principle and process of molten salt electrolysis and metal thermal reduction are introduced. The main sources of metallic impurities and interstitial impurities in rare earth metals as well as the action mechanism of reducing the concentration of different impurities are analyzed and summarized. Then, the purification principle and process of vacuum distillation, arc melting, zone melting, and solid state electromigration are also discussed. Furthermore, the removal effect and function rule of metallic impurities and interstitial impurities in rare earth metals are outlined. Finally, the crucial issues in the development of high purity rare earth metals are put forward, and the development direction of high purity rare earth metals in future are pointed out on this basis.

D2EHPA is a potential extractant for extraction of europium and samarium from chloride medium

Europium and samarium, the most valuable rare earth metals are broadly used in different areas such as fluorescent, medical materials and samarium-cobalt permanent magnet in the industrial community. Solvent extraction is an extensively applied separation process for collection of high purity rare earth metal ions. Due to the congruent physical and chemical properties of rare earth metal ions, the separation of specific elements from the mixture is ambiguous. In such places solvent extraction process is most efficient because of their ease in terms of the equipment and conditions associated with them. Solvent extraction, using di-2-ethylhexylphosphoric acid (D2EHPA) is the most frequently used industrial extractant for the extraction and separation of rare earth metal ions compared with other extractants. Present report deal with the studies on solvent extraction of europium (III) and samarium (III) from chloride medium using D2EHPA diluted in kerosene. Utmost extraction such as 96.65% Eu(III) and 86% Sm(III) happened at 0.001 mol/L hydrogen ion concentration in the aqueous medium. 100% extraction of Eu (III) and Sm(III) has been noticed with 0.07 mol/L and 0.08 mol/L D2EHPA, respectively. The separation factors of Eu/Co and Sm/Co are 1844.44 and 1556, respectively.

Baking process of mineral carrier of rare earth metals with sodium hydroxide using muffle furnace

Rare Earth Elements (REE) is one of the natural resources that are very strategic and high economic value. REE applications in industry are continues to grow such as LCD (liquid crystal display), LED (light emitting diode), magnet and hybrid batteries (NiMH batteries; Misch metal; Ce, La, Nd). This resulted in REE demand continues to increase up to 10%. Increased demand is not matched by the number of Rare Earth production in the world. This happens because the Chinese as the main actor in the producer REE world production (95%) restricting the export of Rare Earth up to 35% so that the world price of LTJ bounced up. Research & development processing, and purification REE continue to obtain high purity Rare Earth Metals. Baking process the mineral carrier of REE (raw material minerals) with solid NaOH using a muffle furnace has been carried out. The research aims to determine the effect of temperature and grain size of the monazite sand on the decomposition reaction monazite sand and reaction kinetics. The raw materials used are monazite sands containing rare earth oxides as much as 55.1% and 11.01% phosphate. At monazite sand baking using solid NaOH will occur monazite sand decomposition process and the release of the existing phosphate. The results showed that the optimal conditions baking process at a temperature of 400°C and 200 mesh particle size obtained 91.40% phosphate inseparable.

Magnetic phase diagrams of Gd-H, Tb-H, Dy-H systems

We study the impact of hydrogen impurity on the magnetic phase transition temperatures of the high purity rare-earth metals Gd, Tb and Dy. Prior to hydrogenation, the rare earths were purified by the vacuum distillation method. Hydrogenation was carried out using a Sievert-type apparatus. Magnetic phase diagrams were constructed based on the thermomagnetic analysis.

Magnetocaloric effect and magnetostrictive deformation in Tb-Dy-Gd-Co-Al with Laves phase structure

The influence of partial substitution of Co by Al atoms on the magnetocaloric and magnetostrictive properties of the multicomponent Tb-Dy-Gd-Co compounds with a Laves phase structure was investigated. The samples were obtained by arc melting using of high-purity rare-earth metals. The crystal structure of Tb0.2Dy0.8-xGdxCo2-yAly (x = 0.3, 0.4, and 0.5; y = 0 and 0.1) compounds was monitored by powder X-ray diffraction. The magnetostriction and the magnetocaloric effect in external magnetic field up to 12 and 18kOe, respectively, were studied in wide temperature range. The Curie temperature of Al-content compounds increases by an average of 20K, while the magnitudes of the magnetocaloric effect and the magnetostriction slightly decrease.

Preparation of High Purity Rare Earth Metals of Samarium, Ytterbium and Thulium

Abstract High purity rare earth metals, including samarium, ytterbium and thulium, were prepared by vacuum reduction-distillation of each rare earth oxide with lanthanum metal. The results show that the rare earth metals of samarium and ytterbium with 4N-purity are obtained by direct vacuum reduction-distillation, and their purity is 99.99 wt% and 99.993 wt%, respectively, with respect to 75 impurities. There is a high concentration of reductant in thulium metal due to the higher reaction temperature and lower distillation velocity ratio of metallic thulium to lanthanum, so that the sublimation purification with lower temperature and high vacuum is needed. The purified thulium can reach a high purity of 99.995wt% with respect to 75 impurities. Therefore, the preparation of high purity reductant of lanthanum metal, especially of total amount control of metallic impurities, is the key step to obtain 99.99%-purity rare earth metallic samarium, ytterbium and thulium

Progress in preparation of rare earth metals and alloys by electrodeposition in molten salts

Rare earth (RE) metals and their alloys have attracted considerable practical interests due to their functional properties. Because of their negative deposition potentials, RE metals cannot be electrochemically deposited from aqueous media. Using molten salt as medium provides a unique opportunity for the electrowinning and electrorefining of high-purity RE metals, as well as for the electrochemical formation of their alloys and intermetallic compounds. Certainly, the electrochemical behaviors of RE metals and their alloys have been investigated in a number of different molten salts comprising all-fluorides, all-chlorides and mixed chloride-fluoride media. Based on the results, RE and their alloys were produced by molten salt electrolysis. In this paper, the developments of preparation of RE metals and their alloys by electrolysis in molten salts in recent years were systematically summarized on both the local and international levels. Attention was paid mainly to the electrodeposition of RE metals and their alloys, including RE–Mg, RE–Al, RE–Ni, RE–Co, RE–Cu, RE–Fe and RE–Zn alloys.

Specific features of determinations of the composition of high-purity lanthanide crystal hydrates

Problem of the determination of the composition of high-purity rare-earth metal salts is discussed. Prospects of the application of direct chemical methods to the determination of the water content of crystal hydrates of rare-earth metal salts used in the GET 173-2013 State Primary Standard of Mass Fraction and Mass (Molar) Concentration of Water in Solid and Liquid Substances and Materials are studied.

Development of nanostructured magnetic materials based on high-purity rare-earth metals and study of their fundamental characteristics

The effect of the structural state on magnetic and hysteretic properties of compounds with high contents of a 3d transition metal, i.e., R2Fe14 − xCoxB and RFe11 − xCoxTi (where R = Y, Sm; 0 ≤ x ≤ 8), was studied. Alloys were prepared using high-purity rare-earth metals by two different methods: induction melting and argon-arc melting. Severe plastic deformation and rapid melt-quenching allowed preparation of nanostructured samples. Structural studies of the samples were performed by X-ray powder diffraction and atomic-force microscopy methods. Magnetic hysteretic properties were studied using a PPMS magnetometer in the temperature range of 4.2–300 K in fields to 20 kOe. It was shown that the dependences of fundamental magnetic parameters (Curie temperature, saturation magnetization, and magnetocrystalline anisotropy constant) on the cobalt content exhibit a similarity for both systems. It was found that, depending on sample treatment, the grain size varies from 30 to 70 nm after severe plastic deformation and in wider ranges (from 10 to 100 nm) after rapid quenching, not exceeding the single-domain size. The interrelation between the microstructure and magnetic characteristics was investigated. It was revealed that the concentration dependence of the coercivity for both systems has a maximum at the same cobalt content, i.e., x = 2.

Specific Heat and Magnetocaloric Effect in Ho-Er-Co Solid Solutions

Specific heat measurements have been performed on polycrystalline HoCo2, ErCo2 and their solid solutions Ho1−x Er x Co2 (0.1≤x≤0.5). These compounds were synthesized using high-purity rare-earth metals and cobalt. X-ray diffraction patterns taken at room temperature reveal that all compounds have the C15 cubic Laves phase structure. Heat capacity measurements have been performed in the temperature range of 2–300 K without magnetic field and in a magnetic field of 1 and 2 T. The magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change for all solid solutions in magnetic fields up to 2 T. The effect of increasing Er amount in Ho1−x Er x Co2 on the magnetic and magnetocaloric properties will be discussed.

Magnetocaloric Effect in Ho-Er-Gd-Co Multicomponent Compounds

We report magnetic and magnetocaloric properties of polycrystalline series of the (Ho0.9Er0.1)1-xGdxCo2(x = 0.05, 0.1 and 0.15) solid solutions. These samples were synthesized using high purity rare earth metals and cobalt. X-ray diffraction patterns taken at room temperature reveal that all compounds have the C15 cubic Laves phase structure. Magnetization measurements were carried out using a vibration sample magnetometer with a step motor in fields up to 14 T using a Bitter-type magnet. Heat capacity measurements have been performed in the temperature range of 2-300 K without magnetic field and in a magnetic field of 1 and 2 T. The magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change for all solid solutions in magnetic fields up to 3 T. The effect of increasing Gd amount in (Ho0.9Er0.1)1-xGdxCo2on the magnetic and magnetocaloric properties will be discussed.

Structural, magnetic, and magnetothermal properties of the Tb0.3Dy0.7Co2 compound

A complex investigation of the structural, magnetic, and magnetothermal properties of the Tb0.3Dy0.7Co2 compound synthesized with the use of high-purity rare-earth metals has been performed. The phase composition has been controlled using the X-ray structural analysis, and the topology of the alloy surface has been investigated using atomic-force microscopy. It has been established that the Tb0.3Dy0.7Co2 compound is single-phase, while the samples selected for measurements possess a clearly pronounced texture. The magnetization has been measured using a vibrating-sample magnetometer in the fields up to 100 kOe in a temperature range from 4.2 to 200 K. The Curie temperature of the compound is 170 K. The data on the temperature dependence of heat capacity of Tb0.3Dy0.7Co2 have been obtained. The magnetocaloric effect ΔT has been measured by a direct method in the fields up to 18 kOe applied both along and perpendicularly to the texture axis. The anisotropic behavior of the magnitude ΔT for this compound, which possesses the cubic structure, has been found. The maximum value of the magnetocaloric effect ΔT = 2.3 K (ΔH = 18 kOe) has been observed upon applying the magnetic field along the texture axis.

Magnetic properties and magnetocaloric effect in (Dy0.6Er0.4)1−xGdxCo2 multicomponent compounds

We report magnetic and magnetocaloric properties of the polycrystalline series of (Dy0.6Er0.4)1−xGdxCo2 (x = 0.2, 0.3 and 0.4) intermetallic compounds. These samples were synthesized using high purity rare earth metals. X-ray diffraction patterns taken at room temperature revealed that all the (Dy0.6Er0.4)1−xGdxCo2 compounds have the C15 cubic Laves phase superstructure. Magnetization measurements were carried out using a vibration sample magnetometer with a step motor in applied fields up to 14 T using a Bitter-type magnet. Heat capacity measurements have been performed in temperature range 2-300 K. The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of heat capacity were estimated. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change for selected solid solutions in magnetic fields up to 3 T. The raising amount of the Gd in samples on magnetic and magnetocaloric properties will be discussed.

Magnetostriction in (Tb0.45Dy0.55)1−xErxCo2 (x = 0.1, 0.2): high-field investigation

Intermetallic compounds (Tb0.45Dy0.55)1−xErxCo2 (x = 0.1; 0.2) were synthesized using high purity rare-earth metals. Multicomponent compositions with compensated magnetic anisotropy (MA) were chosen with respect to theoretical predictions based upon the single-ion MA model. Magnetostriction was measured in magnetic fields up to 10 T within the temperature range of 1.5–200 K by means of strain gauges. In the vicinity of magnetic phase transitions (160–170 K), giant volume magnetostriction (∼2×10−3 in 10 T) provided by the band magnetism of a Co sublattice was observed in the compounds studied.