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《中国稀土学报(英文版)》2022,40(3):467-472
RM3 compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe3 alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y1.1–yScyFe3 (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe3 phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y0.77Sc0.33Fe3 delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y1.1Fe3. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized. 相似文献
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《中国稀土学报(英文版)》2022,40(3):457-461
To investigate the influence of the addition of Pr–Ga alloys on magnetic properties and morphology of materials, the hot-deformed PrNd-Fe-B magnets were prepared by the addition of Pr–Ga alloys using a dual-alloys diffusion. The room-temperature coercivity of the hot-deformed PrNd-Fe-B magnets increases substantially from 1.68 to 2.34 T, while the remanence decreases from 1.42 to 1.24 T, by the addition of 5 wt% Pr–Ga alloys. Moreover, the thermal stability of coercivity improves from ?0.46%/oC to ?0.42%/oC. Two types of grain boundary phases (PrNd-rich and PrNd-Ga-rich) are generated at grain boundaries by microstructural analysis, resulting in the decrease of Fe element concentration from more than 60% to about 10% at grain boundaries. The decrease of ferromagnetic element concentration at grain boundaries and the refinement of grain are considered to be the main reasons for the improvement of coercivity and thermal stability. 相似文献
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《中国稀土学报(英文版)》2022,40(4):660-669
The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd6Fe13Pd1–xCux (x = 0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state are observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔSM in a temperature span of 40 K in the Nd6Fe13Pd0.85Cu0.15 compound are observed. For a field change of 0–5 T, the peak values of –ΔSM for the Nd6Fe13Pd0.95Cu0.05, Nd6Fe13Pd0.90Cu0.10, and Nd6Fe13Pd0.85Cu0.15 compounds are estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle. 相似文献
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《中国稀土学报(英文版)》2022,40(6):981-987
Based on the new process named “Combination Method” for metallurgy and separation of Baotou mixed rare earth concentrate (BMREC), the aim of this paper is to clearly elucidate the phase change behavior of BMREC without additives during oxidative roasting at 450–800 °C. The results indicate that the bastnaesite in BMREC is decomposed at 450–550 °C, the weight loss is about 10.3 wt%, and the activation energy (E) is 144 kJ/mol. The bastnaesite in BMREC is decomposed into rare earth fluoride, rare earth oxides (La2O3, Ce7O12, Pr6O11 and Nd2O3), and CO2, particularly, with the increase of roasting temperature, bastnaesite in BMREC is more completely decomposed into LaF3, which causes a decrease in leaching rate of La during the HCl leaching process. Additionally, the maximum cerium oxidation efficiency reaches about 60 wt% when the roasting temperature is equal to or above 500 °C, and the oxidation reaction rate of cerium increases with the increasing roasting temperature. 相似文献
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《中国稀土学报(英文版)》2022,40(8):1232-1237
Revealing the active species of the catalyst is conducive to the design of more efficient catalyst. Herein, we tried to demonstrate the roles of amorphous and crystalline structures on CePO4 catalyst during selective catalytic reduction (SCR) of NOx by NH3. Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO4. Both amorphous and crystalline CePO4 species on CePO-X samples can provide acid sites for NH3 adsorption, but the former can provide more acid sites. The superior redox property of surface amorphous CePO4 species contributes to its high NH3-SCR activity at low temperature, but it also leads to the decrease of high temperature (>350 °C) NH3-SCR activity due to the oxidation of NH3. In contrast, crystalline CePO4 species shows high activity only at high temperature because of its poor redox property. Therefore, it can be inferred that amorphous and crystalline structures on CePO4 catalyst can be the efficient active species of NH3-SCR at low and high temperature, respectively. 相似文献
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《中国稀土学报(英文版)》2022,40(7):1134-1147
In this study, the Bayan Obo rare earth concentrates mixed with Na2CO3 were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO2 react to form silicates, causing hardening. Further, REPO4 and NaF can directly generate CeF3 and CeF4 at high temperatures, and a part of CeF4 and NaF forms a solid solution substance Na3CeF7. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce0.6Nd0.4O1.8, Ce4O7, and LaPrO3+x. Then, BaSO4, Na2CO3, and Fe2O3 react to form barium ferrite BaFe12O19; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [?ln (1?α)]1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1?(1?α)1/3]2. Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry). 相似文献