Content Of Rare Earth Metals Research Articles

Optimization of Sidoarjo Mud Akaline Fusion Process Using Taguchi Method

Sidoarjo mud contains 48.3% silica which is considered as the biggest impurity when compared to the content of rare earth metals which are 0.3% Eu and 0.02% Yb. The hydrothermal process is used to bind silica as a form of silica extraction activity in the Sidoarjo mud so that the Rare Earth Elements are purified further because their uses are urgently needed. This process compares the alkalis in the form of Na2CO3 and K2CO3 which are basic salts which will then be compared to the most optimum conditions of the two alkalis. Each alkali will be processed under operating conditions following the Taguchi method which aims to minimize research and optimize research results. Based on the research results, it was found that K2CO3 provided better silica recovery than Na2CO3 under operating conditions with a K2CO3 concentration of 2 M, 1 hour soaking time, 700°C melting temperature and 3 hours melting time, giving 95.24% silica recovery. In addition, by using the Taguchi method it can be analyzed that the main factors affecting the melting of the alkali are the melting time, the concentration of the alkali, the temperature of the melting, and the immersion time.

Effects of rare earth metals on microstructure, mechanical properties, and pitting corrosion of 27% Cr hyper duplex stainless steel

Abstract This research focuses on the addition of low-cost rare earth metals (REMs) to improve the comprehensive properties of hyper duplex stainless steels (DSSs). The effects of REM on the microstructure, mechanical properties, and pitting corrosion of hyper DSSs were analyzed by optical/scanning electron microscope metallographic examination, X-ray diffraction analysis, tensile test, impact test, and potentiodynamic polarization test. With the addition of REM, micro/nanoscale REM inclusions were formed, and the microstructure of the alloy was refined. With the increasing content of REM, the average diameter and area of inclusions in the alloy decreased at first and then increased. While the mechanical properties showed a trend of first increasing and then decreasing. An appropriate amount of stable REM inclusions could reduce the susceptibility of pitting corrosion and improve the pitting corrosion resistance of the alloy. The hyper DSSs with REM content in the range of 0.018–0.031 wt% have excellent mechanical properties and pitting resistance.

Compound Boronizing and Its Kinetics Analysis for H13 Steel with Rare Earth CeO2 and Cr2O3

The compound boronizing of H13 steel sample was carried out by adding rare earth CeO2, and the effects of main parameters of compound boronizing on the properties of the boronizing layer were investigated. The boronizing kinetics were also analyzed. Under the conditions of boronizing temperatures of 850 °C, 900 °C, 950 °C, and 1000 °C, and boronizing times of 2 h, 3 h, 4 h, and 5 h, the boronizing experiment was carried out by adding CeO2 with mass fraction of 2%, 4% and 6%, Cr2O3 with a mass fraction of 1%, 2%, 3%, and 4%. The results show that boronizing H13 steel with rare earth CeO2 is conducive to the diffusion of boron atoms and can significantly improve the thickness and microhardness of boronizing layer. Boronizing kinetic analysis shows that the diffusion activation energy of boron atom decreases significantly when the rare earth content is 4%, which indicates that the content of rare earth CeO2 with 4% is an ideal selection for considering improving the utilization rate of rare earth materials, and the boronizing kinetic analysis can provide a quantitative basis for determining the content of rare earth metals. Therefore, experiments and analysis show that for H13 steel, when the boronizing temperature is 950 °C, time is 4 h and rare earth content is 4%, the thickness of the boronizing layer can reach 71 μm and the microhardness at the depth of 70 μm from the surface layer can reach 1546.32 HV. Moreover, on this basis, when Cr2O3 with a rare earth content of 2% is added, the microstructure and wear resistance of the boronizing layer are significantly improved.

Production of aluminum alloy onboard wire with a high content of rare-earth metals produced using electromagnetic crystallization

The Scientific and Production Center for Magnetic Hydrodynamics Ltd has developed an innovative technology for casting long ingots of small diameter (8–12 mm) into an electromagnetic mold (EMM) and manufacturing thin wire (0.5 mm in diameter) from them for onboard wires from 01417 alloy. Crystallization of liquid metal occurs under the influence of electromagnetic forces in an electromagnetic mold with direct supply of coolant to the ingot, due to which cooling rates are achieved that ensure the dispersion of the eutectic phases of rare earth metal aluminides, similarly to how it takes place during the crystallization of granules (~1.103...1.104 K/s). It has been established that the determining parameters in casting ingots are the power supplied to the inductor and the level of the melt above the crystallization front. For the casting to reach a steady state (the process of stabilizing the diameter of the ingot after the start of casting), it is necessary to regulate the melt level for some time. The surface quality of the ingot depends on ensuring stability of the current in the inductor during casting. Fluctuations in the current in the inductor lead to changes in the ingot`s diameter. Casting speed and metal temperature have a great influence on the structure of ingots. In contrast to the method of producing granulated wire with a thin (less than 1 mm) cross-section, which turned out to be problematic due to numerous breaks during drawing associated with the presence of oxide and foreign inclusions, the casting technology in the electromagnetic mold does not require preliminary metal filtration, since oxide and solid non-metallic inclusions are intensively squeezed out by electromagnetic forces onto the ingot`s surface. It has been established that hot deformation of a billet cast in the EMM at the Conform facility provides higher strength characteristics of the wire from the 01417 alloy after drawing compared to the cast annealed billet. Pressing provided an increase in the yield strength and relative elongation of the 01417 alloy by 2 and 2.5 times, respectively, compared with the cast state. As a result, the billet was obtained with high technological plasticity for further drawing. Electron microscopic studies of the wire have been carried out, which have shown that dispersed REM aluminides are rather uniformly distributed over the cross section of the wire with a diameter of 0.5 mm. Determination of the particle size of aluminides at ×50000 magnification showed that their size is ~96–214 nm. Wire from 01417 alloy is used by JSC “Special Design Bureau of the Cable Industry” (JSC “OKB KP”) for the manufacture of conductive cores of installation wires, providing a significant reduction in their weight.

Dissolution kinetics of rare earth metal phosphates in carbonate solutions of alkali metals

Treatment of apatite raw materials is associated with the formation of large-tonnage waste – phosphogypsum. The content of rare earth metals in such waste reaches 1 %, which makes it possible to consider it a technogenic source for obtaining rare earth metals and their compounds. Up to the present moment, there are neither processing plants, nor an efficient process flow to handle phosphogypsum dumps. It is rational to use a way that involves extraction of valuable components and overall reduction of phosphogypsum dumps. Such process flow is available with carbonate conversion of phosphogypsum to alkali metal or ammonium sulfate and calcium carbonate upon the condition of associated extraction of rare earth metal (REM) compounds. Associated extraction of REM compounds becomes possible since they form strong and stable complexes with hard bases according to Pearson, which among other things include carbonate, phosphate and sulfate anions. Formation of lanthanide complexes with inorganic oxygen-containing anions is facilitated by the formation of high-energy Ln-O bonds. The study focuses on the dissolution of lanthanide phosphates in carbonate media. It was established that formation of REM carbonate complexes from their phosphates is a spontaneous endothermic process and that formation of lanthanide carbonates and hydroxides serves as thermodynamic limitation of dissolution. A shift in equilibrium towards the formation of carbonate complexes is achieved by increasing the temperature to 90-100 °C and providing an excess of carbonate. The limiting stage of REM phosphate dissolution in carbonate media is external diffusion. This is indicated by increasing rate of the process with an intensification of stirring, first order of the reaction and the value of activation energy for phosphate dissolution from 27 to 60 kJ/mol. A combination of physical and chemical parameters of the process allowed to develop an engineering solution for associated REM extraction during carbonate conversion of phosphogypsum, which included a 4-5 h conversion of phosphogypsum at temperature of 90-110 °C by an alkali metal or ammonium carbonate solution with a concentration of 2-3 mol/l. As a result, a solution with alkali metal (ammonium) sulfate is obtained, which contains REMs in the form of carbonate complexes and calcium carbonate. The rate of REM extraction into the solution reaches no less than 93 %. Rare earth metals are separated from the mother liquor by precipitation or sorption on anion exchange resins, while the excess of alkali metal or ammonium carbonate is returned to the start of the process.

Investigation structure and properties of wire from the alloy of AL-REM system obtained with the application of casting in the electromagnetic mold, combined rolling-extruding, and drawing

The paper presents the results of studies of the structure and properties of a wire with a diameter of 0.5 mm from an alloy of the Al-REM system with a rare-earth metal content of 7–9%. Wire obtained as a result of the implementation of the technology of its manufacture using the methods of casting into an electromagnetic mold (EMM), continuous extruding, and drawing. The rheological properties of the metal of continuously cast round billets from the experimental alloy obtained using an electromagnetic mold are determined. The modeling and analytical assessment of the possibility of carrying out the process of combined rolling-extruding (CRE) of such billets in a closed box-type roll groove of a continuous extruding unit are carried out. The features of metal shaping have been studied. The temperature-speed and technological parameters were found at which the CRE process can be carried out in a stable mode of operation. Data have been obtained for the forces acting on the die and rolls during rolling-extruding. The results of experimental studies of the process of obtaining longish deformed semi-finished products from an experimental alloy on the laboratory unit CRE-200 and the pilot plant unit CRE-400 are presented. The structure of the metal has been studied; data on the ultimate tensile strength, yield strength, relative elongation, and electrical resistance of hot-extruded rods and wires in cold-worked and annealed states have been obtained. It was found that the proposed processing modes make it possible to obtain by the method of combined rolling-extruding rods with a diameter of 9 mm in industrial conditions from longish billets with a diameter of 18 mm, cast by means of EMM. Wire in a cold-deformed and annealed state with a diameter of 0.5 obtained by drawing from the rods with a diameter of 9 mm from an experimental alloy of the Al-REM system containing 7–9% rare-earth metals with the required physical and mechanical properties.

Development of Combined Machining Modes, Investigation of Mechanical Properties and Structure of Deformed Semi-Finished Products from Alloy 01417

The article presents the results of studies on the production of wire with a diameter of 0.5 mm from aluminum alloy 01417 with a content of rare-earth metals (REM) in the amount of 7-9% for aircraft construction needs. The deformation modes, the experimental technique and equipment for the implementation of the proposed technology described. The wire was obtained by drawing and bar rolling with subsequent drawing from a rod with a diameter of 5 mm, obtained previously using the process of combined rolling-extruding (CRE) from a continuous ingot with a diameter of 12 mm, cast in an electromagnetic mold (EMM). The wire obtained by the presented technology was subjected to 4 different heat treatment modes with annealing temperatures from 350 to 500 °C and holding time of 1 h in the furnace to achieve mechanical and electrophysical properties corresponding to TS 1-809-1038-2018. The level of strength and plastic properties obtained in the course of research required only one intermediate annealing. The microstructure of the wire was investigated and the modes were revealed that made it possible to obtain the required level of mechanical properties and electrical resistivity, satisfying TS 1-809-1038-2018.

Corrosion and wear protection of mild steel substrates by innovative PVD coatings

Today, innovative coatings must ensure wear protection and corrosion resistance for engineering materials with high corrosion susceptibility, e.g. mild steels, as well as the current sustainability criteria in terms of environment protection and health.PVD technology fulfils most of these demands, but unfortunately, the corrosion protection performance is unsatisfactory due to the typically low coating thicknesses of only few micrometres.One solution to overcome the corrosion problem are TiMgREN (RE = Rare Earth) based coatings, which were developed by the authors. Even with 5 μm thick monolithic TiMgGdN coatings a corrosion resistance of at least 800 h could be achieved in the salt spray test without any macroscopic corrosion attack.In the present work, the influence of the coating composition, the substrate material and the surface roughness on the corrosion properties was examined. Besides, the application of Gd as alloying element, the influence and the effect of other rare earth metals (La, Ce) on the corrosion performance were investigated.As benchmark, the TiMgGdN coatings were compared with industrial standard PVD coatings, DLC and electroplated Cr regarding the corrosion and the wear performance.The coatings were characterized concerning their microstructural, mechanical and chemical properties. Salt spray tests as well as electrochemical measurements were carried out to examine the corrosion properties of the coated specimens. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling tests by using a SRV 3 tribometer.It was shown that by variation of the deposition parameters, the coating properties could be improved concerning both, corrosion and wear performance. Furthermore, the effect of the used rare earth metal type and the rare earth metal content on the coating properties was investigated. The TiMgGdN coatings exhibit superior corrosion properties in comparison to the industrial standard coatings.

Изучение растворимости осадков некоторых лантаноидов в карбонатных средах

The study examines the dissolution process for the precipitates of the rare-earth carbonates and phosphates with a change in the concentration parameters of the system. The objective of the study is to determine the nature of the dissolution process at variable composition of the studied solutions. As a result of the theoretical base analysis, the qualitative and quantitative content of rare-earth metals in red sludge and phosphogypsum is presented, which governs the interest in this problem under consideration. The available techniques for extraction of rare-earth metals from red sludge and phosphogypsum have also been considered, their advantages and disadvantages are presented. A promising carbonate-alkali method for the extraction of rare-earth metals has been considered. Thermodynamic parameters of the system have been calculated to determine the possibility of the process. During the experiment the factors affecting the dissolution process have been examined: the carbonate ion concentration, the nature of the solvent cation and rare-earth metal cation. Carbonates and phosphates of europium, holmium, and neodymium have been considered as the analyzed components. Carbonates and phosphates of neodymium, europium, and holmium have been dissolved in model solutions of K2CO3 with the concentrations of 0.2–4.5 mol/L until reaching equilibrium. The obtained results show the dependence of solubility of the precipitates of rare-earth metals on the solvent nature and concentration. The explored data are presented as solubility isotherms. On the basis of experimental data the values of the extraction degree of a rare-earth metal into the solution have been calculated. For neodymium, europium, and holmium carbonates, the maximum recovery degree αmax is 72.8 %, 81.2 %, 83.0 %, respectively. During the experiment with dissolution of lanthanide phosphates, the following results have been obtained: the maximal degree of neodymium extraction is 60.59%, while for europium it equals 51.66 % and 93.01 % for holmium

Structural changes of cerium doped copper ferrites during sintering process and magneto-electrical properties assessment

Abstract Crystalline CuCexFe2-xO4 nanoparticles with different rare earth metal content (x = 0.00, 0.03, 0.05, 0.08 and 0.10) were synthesized using a co-precipitation technique that involves a 600 °C calcination treatment. The newly obtained powders were pressed into pellets and heated up to 950 °C in order to form a compact and less porous material, ideal for dielectric measurements. X-ray investigations revealed a structural modification from typical cubic system to a tetrahedral spinel form, accompanied by Ce3+ cations exclusion and formation of secondary phases. The amount of phases and cations distribution were determined by Rietveld refinement method. A degradation process of cerium doped copper ferrite was proposed based on X-ray analysis and Rietveld refinement. Furthermore, the magnetic behavior of both 600 °C and 950 °C samples was investigated from the hysteresis loops recorded from a vibrating sample magnetometer (VSM) in a ±10 kOe range. Room temperature dielectric values for the 950 °C samples were determined using the parallel-plate capacitor configuration in a frequency range of 10 Hz – 1 MHz.

Coercive Force of (Pr, Dy)–(Fe, Co)–B Sintered Materials with a Low Rare-Earth Metal Content

Sintered (Pr0.53Dy0.47)ΣR(Fe0.77Co0.23)balB7.5 materials are studied. For the Nd–Fe–B-based materials, the calculated neodymium content in the Nd2Fe14B compound is 11.8 at %, whereas an excess neodymium content as compared to that for the stoichiometric composition should be taken for manufacturing magnets. In contrast to the magnets based on the aforementioned system, the magnets based on the Pr–Dy–Fe–Co–B system can be prepared at a lower total rare-earth metal content as compared to that corresponding to the stoichiometric composition. Magnets with a coercive force of 528 kA/m are manufactured at a total rare-earth metal content of 11.5 at %, which is lower than that calculated for the R2(Fe, Co)14B (R = Pr, Dy) phase.

Mechanical Properties of Mg–Dy–Sm–Zr Magnesium Alloys

The mechanical properties of as-cast Mg–Dy–Sm alloys additionally alloyed with zirconium to refine grains in the as-cast state have been studied. The dysprosium and samarium contents are close to their mutual solubility in a magnesium-based solid solution at a homogenization temperature of 515°C, and their total content is 4–12 wt %. The mechanical properties of the alloys have been determined in the states homogenized after casting and aged after homogenization. It is found that the strength properties of the alloys increase to σu ≈ 290 MPa and the plasticity decreases to lower values at a relative elongation δ ≈ 3% as the total content of the rare-earth metals in the alloy increases. The Mg–Dy–Sm–Zr alloys are significantly hardened upon aging, and the age hardening effect increases with the rare-earth metal content in them.

Detection Technology of Metal Elements in Crude Oil and Prospect of Utilization of Metal Resources

There are many kinds of metals in crude oil. The rare metals are essential metals for the development of atomic energy, aviation and space, national defense construction, electronic computer, high point scientific instruments and so on. Although the resources of rare metals are abundant in China, but for a long time, china supplies 90% of the world's rare metals at a relatively low price, the reserves of rare metal resources are declining at an alarming rate. By 2020, only 6 of the 45 major minerals could meet the needs of China. Through the establishment of metal element detection technology in crude oil, the crude oil of Toutai Oil Field in China is determined, and there are rich rare metal elements in the crude oil. For example, the rare-earth metal content is 62.61 micrograms per kilogram, the rare light metals is 78.4 micrograms per kilogram, and the rare refractory metals is 290.47 micrograms per kilogram, etc. Although the research on the prospect of comprehensive utilization of rare metals in crude oil is late in China, the extraction of rare metals from crude oil has a broad prospect.

Recycling of black dross containing rare earths originating from melting and recycling of magnesium alloys

The process of melting and recycling magnesium alloys using fluxes produces a residue termed black dross. The black dross investigated contained metal and non-metallic phases with a considerable content of rare earth metals (REEs). The black dross was separated by crushing and screening into metal and non-metallic fractions. The non-metallic fraction was further processed by water and acid leaching. In the water leach, NaCl, KCl and CaCl2 were separated for crystallisation. In the acid leach the residue was treated with hydrochloric acid in order to dissolve the rare earth elements Ce, La, Nd and Pr. Selective precipitation by oxalic acid and solvent extraction using D2EHPA or PC88A enables a recovery of up to 92.6% of the REEs from the oxide-salt-fraction. The equilibrium isotherms of the solvent extraction operation indicate the potential for further separating the rare earth elements. A flow sheet of the whole processes was developed in order to guide industrial application.

Thermal Properties, Electrochemical Behavior, and Microstructure of Zn-5Sn-2Cu-1.5Bi-xRE High-Temperature Solder

This paper reports the investigation on RE addition into a novel Zn-5Sn-2Cu-1.5Bi-xRE (ZSCB-xRE) high-temperature solder to improve its various performances. The effects of minor rare earth metal (RE) on the thermal properties, microstructure, and electrochemical behavior as well as the mechanical properties of ZSCB-xRE solders were studied. Results showed that when the addition of RE was ≤0.1 wt.%, the change in melting temperature of ZSCB-xRE solder was negligible, but the melting range of the solder alloy decreased. Meanwhile, the measured size, Λ, of nonaligned dendrites of primary e dramatically increased from 57 ± 0.5 to 147 ± 1.3 μm, which plays interdependent roles on the resulting corrosion behavior. ZSCB-xRE solders with much RE content have much higher Λ. This is shown to be a driving-force leading to the increase in the corrosion resistance and mechanical properties of ZSCB-xRE solders.

Origin of uranium and rare earth minerals in bone detritus from rare metal deposits

In order to ascertain the forms in which uranium is present in ores of the Melovoe rare metal sedimentary deposit of uranium and rare earth minerals (South Mangyshlak), we investigated a series of typical ore samples that were collected earlier; both the uranium content and the total content of rare earth metals in them lay within 0.1–0.3%. The study was carried out by analytical electron microscopy using transmission electron microscopy and scanning electron microscopy, electron microdiffraction, and microprobing. It was ascertained that both uranium and rare earth elements are present in ore mostly associated with biogenic phosphate in the form of natural minerals, such as uraninite, ningyoite, coffinite, autenite, and churchite. Iron hydroxides and graphitized organic matter are present in some samples. It is assumed that the co-occurrence of uranium and rare earth elements, which is nontypical for the sedimentary process, resulted from secondary epigenetic processes and alternation of reducing and oxidizing environmental conditions.

Polymer nanoencapsulated rare earth aerogels: chemically complex but stoichiometrically similar core–shell superstructures with skeletal properties of pure compounds

Rare earth (RE) aerogels combine the typical high porosity of aerogels with useful electrical, magnetic, optical and catalytic properties of the skeletal framework. RE aerogels were prepared by supercritical fluid CO2 drying of wet gels, which in turn were obtained via a modification of literature procedures involving epichlorohydrine-induced gelation of ethanolic solutions of the hydrated chlorides. But even more so than their silica counterparts, RE aerogels are fragile materials. This problem is addressed by using the innate hydroxyl functionality of the mesoporous surfaces as the focal point for casting a conformal polyurethane/polyurea layer over their entire inorganic framework, thus preserving most of the mesoporosity of the native network (70% v/v after vs. 94% v/v before applying the polymer layer) and a significant portion of the mesoporous surface area (156 ± 19 m2 g−1 after vs. 368 ± 14 m2 g−1 before casting the polymer). Detailed chemical analysis shows that RE aerogels are far from pure oxides. For example, the RE metal content (Pr to Lu) is in the range of 58.0 ± 2.3% w/w, vs. 85.4–87.9% in the pure oxides. RE aerogels contain also carbonate, chloride and organic products from the gelation process. Despite their chemical complexity, however, both native and polymer encapsulated RE sol–gel materials are stoichiometrically similar, and by using the magnetic susceptibility as a probe, it is found that physical properties depending on the atomic number (AN) of the RE core element vary linearly with those of pure RE compounds. Therefore, from an applications design perspective RE sol–gel materials themselves can be treated as pure compounds. By analogy, similar types of core–shell structures and the associated benefits should be possible for all sol–gel materials.

New rare earth metal-rich indides RE14Ni 3In 3 ( RE=Sc, Y, Gd–Tm, Lu)—synthesis and crystal chemistry

The rare earth–nickel–indides RE 14Ni 3In 3 ( RE = Sc , Y, Gd–Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing. The compounds were investigated on the basis of X-ray powder and single crystal data: Lu 14Co 2In 3 type, P4 2/ nmc, Z = 4 , a = 888.1 ( 1 ) , c = 2134.7 ( 4 ) , w R 2 = 0.0653 , 1381 F 2 values, 63 variables for Sc 13.89Ni 3.66In 2.45; a = 961.2 ( 1 ) , c = 2316.2 ( 5 ) , w R 2 = 0.0633 , 1741 F 2 values, 64 variables for Y 13.84Ni 3.19In 2.97; a = 965.3 ( 1 ) , c = 2330.5 ( 5 ) , w R 2 = 0.0620 , 1765 F 2 values, 63 variables for Gd 14Ni 3.29In 2.71; a = 956.8 ( 1 ) , c = 2298.4 ( 5 ) , w R 2 = 0.0829 , 1707 F 2 values, 64 variables for Tb 13.82Ni 3.36In 2.82; a = 951.7 ( 1 ) , c = 2289.0 ( 5 ) , w R 2 = 0.0838 , 1794 F 2 values, 64 variables for Dy 13.60Ni 3.34In 3.06; a = 948.53 ( 7 ) , c = 2270.6 ( 1 ) , w R 2 = 0.1137 , 1191 F 2 values, 64 variables for Ho 13.35Ni 3.17In 3.48; a = 943.5 ( 1 ) , c = 2269.1 ( 5 ) , w R 2 = 0.0552 , 1646 F 2 values, 64 variables for Er 13.53Ni 3.14In 3.33; a = 938.42 ( 7 ) , c = 2250.8 ( 1 ) , w R 2 = 0.1051 , 1611 F 2 values, 64 variables for Tm 13.47Ni 3.28In 3.25; a = 937.3 ( 1 ) , c = 2249.6 ( 5 ) , w R 2 = 0.0692 , 1604 F 2 values, 64 variables for Tm 13.80Ni 3.49In 2.71; and a = 933.4 ( 1 ) , c = 2263.0 ( 5 ) , w R 2 = 0.0709 , 1603 F 2 values, 64 variables for Lu 13.94Ni 3.07In 2.99. The RE 14Ni 3In 3 indides show significant Ni/In mixing on the 4 c In1 site. Except the gadolinium compound, the RE 14Ni 3In 3 intermetallics also reveal RE/In mixing on the 4 c RE1 site, leading to the refined compositions. Due to the high rare earth metal content, the seven crystallographically independent RE sites have between 9 and 10 nearest RE neighbors. The RE 14Ni 3In 3 structures can be described as a complex intergrowth of rare earth-based polyhedra. Both nickel sites have a distorted trigonal-prismatic rare earth coordination. An interesting feature is the In2–In2 dumb-bell at an In2–In2 distance of 304 pm (for Gd 14Ni 3.29In 2.71). The crystal chemical peculiarities of the RE 14Ni 3In 3 indides are briefly discussed.

Effect of Partial Substitutions of Rare-earth Metals for Na-site on the Thermoelectric Properties of Na<SUB><i>x</i></SUB>Co<SUB>2</SUB>O<SUB>4</SUB> Prepared by the Polymerized Complex Method

Polycrystalline (Na 1 - y M y ) x Co 2 O 4 (M=Nd, Sm, Dy and Yb; y = 0.01 ∼ 0.05) samples were synthesized by a polymerized complex method. The effects of partial substitution of rare-earth metals for a Na-site on the thermoelectric properties of Na x Co 2 O 4 were investigated, and their differences with the sample prepared by a conventional solid-state reaction (SSR) method were evaluated. In case of the Nd, Sm and Dy-substituted samples, each rare-earth metal content in the matrix phase was slightly higher than that of the sample prepared by the SSR method, resulting in the slight increase in the thermoelectric power. Dy-substituted samples with y = 0.03 and 0.05 showed the decrease in the electrical resistivity compared to the non-substituted sample because of the enhanced c-axis orientation. The power factors of the Dy-substituted samples were higher than that of the non-substituted sample over the entire temperature range, and the sample with y = 0.05 showed the maximum power factor value of 1.5 x 10 - 3 Wm - 1 K - 2 at 1073 K. On the other hand, Yb-substituted samples with y ≤ 0.03 were almost single Na x Co 2 O 4 phase. The maximum Yb content in the matrix phase corresponded to y . = . 0.03 from the EDX analysis. The value was remarkably higher than that of the sample prepared by the SSR method. For the Yb-substituted samples with y < 0.03, the c-axis orientation was enhanced with increasing the nominal Yb composition in conjunction with the rise in the lattice parameter, c. The Yb substitution caused the increase in the electrical resistivity and thermoelectric power compared to the non-substituted sample over the entire temperature range, which is considered to be due to the reduction in the carrier density resulted from the Yb substitution for Na-site. The power factor of the sample with y = 0.03 was enhanced over the entire temperature range, and the maximum power factor, 1.5 × 10 - 3 Wm - 1 K - 2 was obtained at 1073 K.

Effects of Rare Earth Metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.