Rare Earth Oxide Powders Research Articles

An Integrated Hydrometallurgical Treatment and Combustion Process for Sustainable Production of Sm2O3 Nanoparticles from Waste SmCo Magnets

Samarium (Sm), as one of the rare earth elements (REEs), has gained significant attention in the production of SmCo magnets due to their high corrosion and oxidation resistance, as well as their high-temperature stability. SmCo magnets find applications in various industries, including but not limited to national defense, aerospace, military, and medical equipment. Sm and Co have been classified as a critical metal due to its economic importance and supply risk. Recovering Sm from SmCo magnets is an effective method to ensure a stable supply. The present study investigates an integrated hydrometallurgical treatment and combustion process for the preparation of rare earth oxide (Sm2O3) powders from SmCo. Initially, SmCo powders is exposed to nitric acid, and the resulting slurry is selectively oxidized at 250 °C to obtain Sm(NO3)3, Co2O3, and Fe2O3. Subsequently, the selectively oxidized powders are leached with water to extract Sm. Sm2O3 powders are produced from the obtained leaching solution using an energy- and time-efficient solution combustion process. In this process, once the ignition point of the leaching solution-citric acid complex is reached, combustion occurs and concludes within a short time. The combusted powders are then calcined at different temperatures to produce crystalline Sm2O3 powders. Finally, the optimal conditions for the production of Sm2O3 are identified, and the produced powder is characterized through XRD and FESEM analysis.

Comparison of production of mixed rare earth oxide (Nd/Pr oxide) powders by different precipitation agents from NdFeB magnets’ water leaching

ABSTRACT This research compared the production processes for mixed rare earth oxide (Nd/Pr oxide) powders from a leach solution obtained from acid baking with nitric acid followed by water leaching. Furthermore, the precipitation behaviour of the constituent elements in the leach liquor was examined. Development of economically feasible processes is significant on an industrial scale. In this regard, Nd/Pr oxide powders were recovered from the leach solution by using oxalic acid, ammonium oxalic acid (C2H2O4), sodium hydroxide (NaOH), and ammonium hydrogen carbonate (NH4HCO3) in a comparative manner. Experimental investigations showed behavioural similarities between C2H2O4 and NH4HCO3 precipitation agents; they precipitate rare earth elements (REEs), selectively. However, NaOH was different from them as it precipitates constituent elements in the leach liquor. The cost of C2H2O4 and NH4HCO3 on the industrial scale is higher than NaOH. The resulting flow diagrams of the preparation of Nd/Pr oxide powders were comprehensively compared and optimised to propose more environmentally friendly, economical, and sustainable process.

A solar optical hyperspectral library of rare-earth-bearing minerals, rare-earth oxide powders, copper-bearing minerals and Apliki mine surface samples

Abstract. Mineral resource exploration and mining is an essential part of today's high-tech industry. Elements such as rare-earth elements (REEs) and copper are, therefore, in high demand. Modern exploration techniques from multiple platforms (e.g., spaceborne and airborne), to detect and map the spectral characteristics of the materials of interest, require spectral libraries as an essential reference. They include field and laboratory spectral information in combination with geochemical analyses for validation. Here, we present a collection of REE- and copper-related hyperspectral spectra with associated geochemical information. The libraries contain reflectance spectra from rare-earth element oxides, REE-bearing minerals, copper-bearing minerals and mine surface samples from the Apliki copper–gold–pyrite mine in the Republic of Cyprus. The samples were measured with the HySpex imaging spectrometers in the visible and near infrared (VNIR) and shortwave infrared (SWIR) range (400–2500 nm). The geochemical validation of each sample is provided with the reflectance spectra. The spectral libraries are openly available to assist future mineral mapping campaigns and laboratory spectroscopic analyses. The spectral libraries and corresponding geochemistry are published via GFZ Data Services with the following DOIs: https://doi.org/10.5880/GFZ.1.4.2019.004 (13 REE-bearing minerals and 16 oxide powders, Koerting et al., 2019a), https://doi.org/10.5880/GFZ.1.4.2019.003 (20 copper-bearing minerals, Koellner et al., 2019), and https://doi.org/10.5880/GFZ.1.4.2019.005 (37 copper-bearing surface material samples from the Apliki copper–gold–pyrite mine in Cyprus, Koerting et al., 2019b). All spectral libraries are united and comparable by the internally consistent method of hyperspectral data acquisition in the laboratory.

Fabrication of Gd2O2S:Pr scintillation ceramics from water-bath synthesized nanopowders

Crystallized precursor (Pr,Gd)2(OH)4SO4·nH2O with stacked layered structure was prepared through a simple water-bath method with rare earth oxide powders and concentrated sulfuric acid as the only starting materials. Phase transformations of the precursor in air or reducing atmosphere together with various calcining temperature were investigated. Pure Gd2O2S:Pr nanopowder that obtained by reducing the precursor under flowing hydrogen atmosphere remained same layered structure as the precursor. The Gd2O2S:Pr scintillation ceramics with the relative density over 99% of theoretical value were prepared through pre-sintering in vacuum followed by HIP post-treatment in argon atmosphere. Under X-ray excitation, bright green emission centered at 511 nm could be observed in both Gd2O2S:Pr powders and ceramics due to the 3P0–3H4 transition of Pr3+. CIE chromaticity coordinates of (0.232, 0.610) and (0.253, 0.596) correspond to the PL and XEL luminescence of the ceramics, respectively. The photoluminescent lifetime of Pr3+3P0–3H4 transition was measured to be 6.73 μs under 337 nm excitation. Method for preparing GOS powder and ceramics in this work is relatively simple and environmentally friendly and is expected to be applied in the preparation of rare earth ions doped GOS materials.

Blue–Green Emission in Terbium‐Doped Alumina (Tb:Al2O3) Transparent Ceramics

AbstractAlumina (Al2O3) is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium‐doped single crystal Al2O3was the basis for the first laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition‐metal dopants because RE doping produces greater efficiencies and lower lasing thresholds. RE‐doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al2O3suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE (∼10−3%) in Al2O3in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb3+ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light‐emitting ceramic. Sub‐micrometer alumina and nanometric RE oxide powders are simultaneously densified and reacted using current‐activated, pressure‐assisted densification (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission (∼75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb3+emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.

열차폐용 희토류 산화물의 상형성과 열물성

Thermal barrier systems have been widely investigated over the past decades, in order to enhance reliability and efficiency of gas turbines at higher temperatures. Yttria-stabilized zirconia (YSZ) is one of the most leading materials as the thermal barriers due to its low thermal conductivity, thermodynamic stability, and thermal compatibility with metal substrates. In this work, rare-earth oxides with pyrochlore phases for thermal barrier systems were investigated. Pyrochlore phases were successfully formed via solid-state reactions started from rare-earth oxide powders. For the heat-treated samples, thermo-physical properties were examined. These rare-oxide oxides showed thermal expansion of <TEX>$9{\sim}12{\times}10^{-6}/K$</TEX> and thermal conductivity of 1.2~2.4 W/mK, which is comparable with the thermal properties of YSZ.

Upconversion for White Light Generation by a Single Compound

A new multiphoton upconversion process for rare earth oxide powders is reported, using infrared laser diodes. In vacuum, multiphoton excitation produces intense upconversion emission in the visible spectral range, and Tm(2)O(3) or Yb(2)O(3) achieves pure white upconversion using 808 or 975 nm excitation, respectively.

Mechanical Properties of α- and β-SiAlON Composite Ceramics Using β-SiAlON Powder

β-SiAlON powder was used as a raw powder to fabricate α/β-SiAlON composite ceramics with different rare earth elements. The phases present in the sample fabricated from -SiAlON, α-Si3N4, AlN, and rare earth oxide powders were - and -SiAlONs. The composition was dependent on the chemical composition and firing profile. The sample obtained by adding Yb2O3 had a high -SiAlON content. The /-SiAlON composite ceramics had high densit. Their microstructures depended on the used metal oxides, namely, the addition of Nd2O3 and CaCO3 resulted in the elongation of the -SiAlON grains. The bending strength, fracture toughness, and hardness were influenced by the -SiAlON content, amount of elongated grains, and density of the sample.

Phase transformation of ultrafine rare earth oxide powders synthesized by radio frequency plasma spraying

Inductively coupled radio frequency plasma spraying was used to prepare ultrafine powders of Sm 2O 3, Dy 2O 3, and Lu 2O 3. These three materials were studied because they are effective dopants in multi-layer ceramic capacitors (MLCC) to improve lifetime. The as-sprayed powders consist of both micron-sized mono-dispersed spherical particles and nano-sized particles in various shapes. In addition to the spheroidization effect, plasma treatment leads to an increase of the monoclinic phase fraction associated with a corresponding decrease of the amount of the cubic phase. The degree of this phase change was found to depend sensitively on the sprayed oxides, decreasing with increasing atomic number of the rare earth element, which is associated with their thermodynamic stability. Furthermore, the monoclinic high-temperature equilibrium phase induced by plasma treatment remains stable at room temperature and even during annealing at a temperature of 900 °C.

Dispersion and Flocculation Behavior of Rare Earth Oxide Powders in Organic Solvent.

Dispersion and Flocculation Behavior of Rare Earth Oxide Powders in Organic Solvent.

（Ｌａ１−ｘＬｎｘ）２Ｏ２ＣＮ２（Ｌｎ＝Ｐｒ，Ｓｍ，Ｅｕ，Ｔｂ）の合成と蛍光特性

Several rare earth doped lanthanum dioxymonocyanamide phosphors have been prepared by calcining mixture of La2O3 and rare-earth oxide powders under flowing ammonia gas in the existence of carbon. Incorporated rare earth ions worked as a luminescence center. Colors of the luminescence of these phosphors irradiated by the monochromatized x-ray of 9keV were pale blue, reddish purple, red and green for Pr, Sm, Eu and Tb, respectively. For optical luminescence spectra measured for (La1-xEux)2O2CN2 at room temperature, the relation between the fluorescence intensity and Eu content, x was discussed with the solid solution limit of Eu to La2O2CN2, estimated by the XRD and XANES analyses.

Effective thermal conductivity and thermal diffusivity of some rare earth oxides

Thermal conductivity and thermal diffusivity of three rare earth oxide powders (Gadolinium oxide, Samarium oxide and Yttrium oxide) are measured experimentally using Transient Plane Source (TPS) technique at ambient temperature. An attempt has been made to accommodate the effect of porosity of the powders on thermal conductivity. Calculation of effective thermal conductivity on the basis of a theoretical model has been carried out and it has been found that the theoretical results are in good agreement with the experimental values. Further it has been shown that the TPS technique is an effective method for the measurement of thermal conductivity of powders.

Application of screen‐printed rare earth oxide protective film to alternating‐current plasma display panels

AbstractScreen‐printed protective film of rare earth oxides (La2O3, Gd2O3, Dy2O3, Y2O3, and Yb2O3) was applied to ac‐plasma display panels. Screen‐printed rare earth protective films have higher luminous efficiencies than a sputtered MgO protective film. However, it is difficult to obtain a low firing voltage (Vf) from screen‐printed rare earth oxide protective films.Only the La2O3 protective film has a lower firing voltage than the sputtered MgO protective film. Gd2O3 has the lowest sustaining voltage (VS) which is 54 V lower than that of the sputtered MgO protective film. Since rare earth oxide powders with high crystallinity exhibit superior discharge characteristics, it is necessary to improve the crystallinity of the powders. In order to obtain a high luminous efficiency, it is necessary to have a low discharge current. Both Y2O3 and La2O3 have a high current‐limiting effect. The current‐limiting effect is related closely to cell resistance. Since Dy2O3 has a low cell resistance, its current‐limiting effect is low. Gd2O3 has the highest luminance per unit discharge current. If it is possible to reduce the discharge current of Gd2O3 further, it is possible to obtain a higher luminous efficiency. Every screen‐printed rare earth oxide film has an excellent protective effect. However, from the viewpoint of low discharge voltage and high luminous efficiency, La2O3 and Gd2O3 are superior to all other rare earth oxides due to their low discharge voltage and high luminous efficiency.

Bicolor pyroreflectometer using an optical fiber probe

A method and a device to measure temperature using bicolor optical pyrometry are presented. The device is equipped with an optical fiber probe designed for in situ measurements in severe conditions (high temperatures, difficult accessibility, and electromagnetic fields). The directional monochromatic emissivities, at two wavelengths 1.3 and 1.55 μm, were deduced from reflection measurements. The device can be used for opaque Lambertian surfaces in the temperature range from 500 to 2500 °C. The method was put in practice on rare-earth metal oxide powders at temperatures up to 1000 °C.

Effect of rare-earth oxide addition on the thermal conductivity of sintered aluminium nitride

The densification of A1N ceramics and the improvement of its thermal conductivity are typically achieved by the addition of a small amount of oxides. The effects of oxide addition on the density and thermal conductivity of sintered A1N were investigated by Tsuge and co-workers [1, 2]. They found that the alkaliand rare-earth oxides (Re203) were useful additives for the fabrication of fully densified and highly thermally conductive A1N; Y203 is an especially good sintering additive. In the A1N sintering process, Y203 additive reacts with the surface oxide layer of A1N particles, forms the liquid phase of the Y A I O N system, causes the precipitation of yttrium-aluminium-oxide phases such as Y4A1209 (2Y203.A1203) in grain boundaries and lowers the oxygen content dissolved in A1N grains, and then the thermal conductivity of sintered A1N increases [2]. However, the effects of Re203 addition other than Y203 on the thermal conductivity of A1N have not been studied in depth. Recently A1N sintering with Y203 additive under reducing nitrogen gas atmosphere was reported to be a useful method to obtain sintered bodies with high thermal conductivity (>150 W m -a K -1) [3-7]. In this study the effects of Re203 addition on the thermal conductivity of A1N specimens sintered in reducing nitrogen atmosphere were investigated. A commercial A1N powder (Tokuyama Soda Co., Tokyo) with an average particle size of 0.6/xm and a specific surface area of 3.2 m 2 g-1 was used in this research. According to the manufacturer, this powder contains 1 wt % oxygen, 220 p.p.m, carbon and trace amounts of iron, calcium and silicon. In this work ND203, Sm203, Gd203, Dy203, Er203 and Yb20 3 powders (Hokko Chemicals Co., Tokyo) were used as the Re203 additives. I mol % of each of the rare-earth oxide powders as sintering aids were added, respectively, to the raw A1N powder. These powders were mixed in ethanol in a ball mill. After drying, the mixed powder was formed into pellets 14 mm in diameter and 8 mm high using a stainless steel die, and then cold isostatically pressed (CIPed) under 200 MPa pressure for 60 s. The CIPed pellets were placed in a graphite crucible, and then sintered using a graphite heater furnance at temperatures of 1773, 1873, 1973, 2073 and 2173 K for 1 and 3 h under 0.1 MPa nitrogen atmosphere. Furthermore, the CIPed samples were sintered in a graphite crucible with A1N packing powder in order to investigate the effect of the sintering atmosphere. The heating rate was 0.17 Ks Gd203 > Er203 > Yb203 >Nd203 >Sm203 addition. On the other hand, in sintering with packing powder, the thermal conductivity of A1N specimens with Re203 were about 95 W m -1K -1. The maximum thermal conductivity of A1N ceramics obtained in this work was 195 W m -1K -a for Dy203 addition. The results for the oxygen content of sintered A1N with the Re203 are shown in Fig. 2. The oxygen content of A1N specimens sintered without packing

Production of highly-sinterable rare-earth oxide powders by controlled humidity dewatering of precursors

Production of highly-sinterable rare-earth oxide powders by controlled humidity dewatering of precursors

A new technique for making enriched rare-earth mental plate targets

A new method for making isotopically enriched rare-earth metal plate targets such as 142Nd, 158Gd, 164Dy, and 166Er, for use in neutrino mass measurements as well as other experiments, was developed. The preparation method is very simple and involves the fluorination of rare-earth oxide powders followed by a Ca reduction using RF heating. The resulting metal was pressed with a hot-press device in an argon atmosphere and rolled into large area plates with areal densities greater than or equal to 85 mg/cm 2. A detailed description of the preparation processes is given as well as the estimation of their efficiencies.

Photoacoustic Spectroscopy of Rare Earth Oxides

A collection of photoacoustic spectra of several readily available stoichiometric rare earth oxide powders is presented. J levels of these spectra are assigned. In addition to the traditional applications of photoacoustic spectroscopy (chemical, physical, and analytical investigations), the technique is useful for studying the kinetics and thermodynamics of intermediate phases of rare earth oxides and surface photochemical reactions of rare earth oxides. The spectra may also reveal information on the lattice structure of powder grains. The need for additional work in rare earth oxide spectroscopy is pointed out.

Production of highly-sinterable rare-earth oxide powders by controlled humidity dewatering of precursors

The sintering behavior of rare-earth oxide powders produced from reverse strike hydroxide, oxalate and carbonate precursors was studied. The influences of controlled humidity dewatering of precursors on powder morphology and sintering behavior were extensively studied, and were compared with those produced by oven drying or dewatering by using organic washes (ATA method). Significant differences in behavior were observed for hydroxide- and carbonate-derived powders dewatered in different ways; oxalate-derived powders showed little behavioral dependence on dewatering method. In general, controlled humidity dewatering proved effective in leading to highly-sinterable powders from any of the three precursors investigated, ATA treatment was effective for hydroxide and oxalate precursors, and oven drying generally led to good sinterability only for oxalate-derived powders. Compaction behavior and surface area of the powders were also determined and attempts were made to correlate these characteristics with sintering behavior.

Electret microphone for use in photoacoustic spectrometer and photoacoustic spectrum of some rare earth oxide powders

We describe a new method for the polarization of an electret foil which has proved very convenient and yields a foil having very good performance in a microphone. The variations in the charge accumulation on the electret foil and its decay with time as well as the variation of the microphone sensitivity with different microphone parameterse.g. different thicknesses of the electret foil, different back plates and different polarization techniques has been investigated. The sensitivity of the home-made microphone is estimated as 1 mV/μbar. The working of this type of microphone and its comparison with a commercial microphone as used in a (laboratory made) single beam photoacoustic spectrometer is discussed.