Diffusion Coefficient Of Nd Research Articles

TMPAC-EG deep eutectic solvent for sustainable recovery of Nd by electrodeposition

The electrodeposition of neodymium (Nd) in a novel analogous ionic liquid (AIL), phenyltrimethylammonium chloride-ethylene glycol (TMPAC-EG), was investigated. The existence form and the electrochemical behavior of Nd(III) in TMPAC-EG were studied using spectroscopic, cyclic voltammetry and chronoamperometry analyses. The spectroscopic analyses indicates that Nd3+ interact with Cl− and EG to form complexes [Nd(EG)6-yCly]3-y as NdCl3 dissolves in TMPAC-EG IL. Cyclic voltammograms reveals that the overpotential for Nd electrodeposition in TMPAC-EG IL decreases with the rise of the temperature. The diffusion coefficient of Nd(III) ions is calculated to about 10−12 m2 s−1. The diffusion activation energy for Nd(III) ions is determined to be 22.8 kJ mol−1 from the temperature dependence of diffusion coefficient. The transient analysis indicates that initial nucleation behavior of Nd conforms to the three-dimensional instantaneous nucleation and growth model, which are largely independent of temperature. In addition, deposition temperature and deposition potential are found to have a great influence on the nucleation and growth kinetics of Nd electrodeposition. Depending on the temperature and potential of electrodeposition, metallic neodymium with caterpillar-shape, nodule, layered rock, or porous structures was obtained.

Electrodeposition of neodymium from betaine-ethylene glycol deep eutectic solvent using neodymium oxide as a precursor

The electrodeposition of neodymium was investigated in betaine-ethylene glycol (Bet-EG) deep eutectic solvent (DES) containing neodymium oxide (Nd2O3) at different temperatures ranging from 353 K to 373 K. The electrochemical behavior of Nd2O3 dissolved in Bet-EG DES was researched by cyclic voltammetry, potentiodynamic polarization and chronoamperometry methods. Cyclic voltammograms (CVs) manifest that Nd(III) reduction in Bet-EG is an irreversible process with diffusion-controlled, and the reduction overpotential of Nd(III) decreases with the increase of the temperature. The temperature has an impact on the diffusion coefficient of Nd(III) species, obeying the Arrhenius equation. The activation energy is estimated to be 36.78 kJ mol−1. The cathodic polarization analysis shows that the rise of temperature promotes the reduction of Nd(III). The UV–Vis and ESI-MS analyses show that [Nd2(bet)8(H2O)4]6+ complex anions are formed as Nd2O3 is dissolved in Bet-EG DES. Electrodeposited neodymium with various morphologies were characterized and analyzed by EDX, XPS, XRD and SEM. It is found that the electrodeposition temperature has a great effect on the morphology of Nd electrodeposits. Depending on the deposition temperature, metallic Nd with submicron particles or porous structures were obtained.

Bulk and surface diffusion of neodymium in alpha-uranium: Ab initio calculations and kinetic Monte Carlo simulations

• A Nd interstitial is found to be intrinsically unstable in alpha- U . • The binding between the substitutional Nd and the U vacancy in strong in alpha- U . • Nd atoms migrate in bulk alpha- U via the vacancy mechanism. • Radiation can significantly accelerate the bulk diffusivity of Nd in alpha- U . • Diffusion of Nd adatoms via pore surfaces is much faster than bulk diffusion. A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and kinetic Monte Carlo (KMC) study of the bulk diffusivity of Nd in α-U , fully taking into account the effect of radiation enhanced diffusion. The vacancy mechanism is considered to be the dominant mechanism for the bulk diffusion of Nd since a Nd interstitial is found to be intrinsically unstable in α-U . The surface diffusivity of a Nd adatom on α-U (001) surface has been further predicted using KMC simulations parameterized by DFT calculations. The present study suggests that Nd transport via the surface diffusion mechanism can be many orders of magnitude faster than bulk diffusion. Furthermore, the results from the present lower length scale study can be used to inform mesoscale phase-field simulations to determine the effective diffusion coefficient of Nd through α-U with a porous microstructure.

Electrochemical Behavior of Nd and the Preparation of Mg-Al-Nd Alloys in LiCl-NaCl Molten Salt

The electrochemical behaviors of Nd(Ⅲ) ions and the mechanism of Mg-Al-Nd alloys by co-reduction were studied in LiCl-NaCl-MgCl2 melts by cyclic voltammetry(CV). The results of CV indicates that Nd(Ⅲ) ion was reduced to Nd atom in two steps exchange 3 electrons: Nd(Ⅲ)+e-=Nd(Ⅱ) and Nd(Ⅱ)+2e-=Nd(0). The diffusion coefficients of Nd(Ⅲ) was calculated and found to be 4.92×10-5 cm2 s-1. Mg-Al-Nd alloy samples prepared by galvanostatic electrolysis were analyzed by XRD and SEM-EDS. Results indicate that when there is no Nd2O3 in the melts, the alloying phases are mainly Al12Mg17, Al0.58Mg0.42 and Mg phases. When 0.35% Nd2O3 was added into the melts, only Al2Nd and Mg phases exist in the alloy; Nd element mainly distributes at grain boundary, Al element distributes in grain boundary and cell, and Mg elements distribute in the whole alloy as the matrix of the alloy. Acknowledgement The work was financially supported by the National Natural Science foundation of China (11675044, 11575047, 21790373, 21271054 and 21173060), the Major Research plan of the National Natural ScienceFoundation of China (91326113 and 91226201), and the International Exchange Program of Harbin Engineering University for Innovation−oriented Talents Cultivation.

Purification of rare earth bis(trifluoromethyl-sulfonyl)amide salts by hydrometallurgy and electrodeposition of neodymium metal using potassium bis(trifluoromethyl-sulfonyl)amide melts

This paper reports a novel bench-scale hydrometallurgical procedure and electrodeposition using potassium bis(trifluoromethyl-sulfonyl)amide (KTFSA) melts for the recovery of rare earth (RE) elements from Nd-Fe-B magnet waste. The investigations were performed at bench scale to assess the potential of a process based on leaching, deironization, and purification of RE amide salts. In the leaching process using 3.4 kg of oxidized Nd-Fe-B and 14.2 L of an aqueous solution of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA), 83.0% Nd and 0.98% Fe were leached in 13 h, indicating that selective leaching of RE elements was performed at bench scale. Then, KOH or oxidized Nd-Fe-B was used as a precipitation agent in the deironization process and 100.0% Fe was successfully separated from RE components. Moreover, 4.07 kg of purified amide salts (M(TFSA)3, M = Pr, Nd, Dy, B, Al, and trace elements) were recovered from a spray dryer. The electrochemical behavior of Nd(III) in KTFSA melts containing M(TFSA)3 (molar fraction of RE components: xRE = 0.1) was investigated in this study. Electrochemical analysis revealed that the reduction peak of Nd(III) at around +1.0 V vs. K/K+ was due to the following reaction: Nd(III) + 3e− → Nd(0). The diffusion coefficient of Nd(III) was estimated to be 3.14 × 10−10 m2 s−1 at 483 K by semi-differential analysis, which is similar to that of Nd(III) in KTFSA melts containing pure Nd(TFSA)3 salts (xNd = 0.1). The electrodeposition of Nd was performed under potentiostatic conditions of +0.8 V vs. K/K+ at 483 K. The electrodeposits had a fine surface morphology with small metal particles. The electrodeposits were confirmed to be Nd metal in the middle layer analyzed by scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Finally, we demonstrated the effectiveness of the novel recovery process for practical use by estimating whole material flow.

Electrochemical analysis of diffusion behavior and nucleation mechanism for neodymium complex in potassium bis(trifluoromethylsulfonyl)amide melts

The electrochemical behavior of Nd(III) in potassium bis(trifluoromethyl-sulfonyl) amide (KTFSA) melts was investigated in this study. It is speculated that the first reduction peak around +2.3V likely corresponds to the formation of Nd(II). The electrochemical analysis revealed that the reduction peak of Nd(III) around +1.0V would be based on the following reaction; [Nd(III)+3e−→Nd(0)]. The diffusion coefficient of Nd(III) in KTFSA melts was estimated to be 4.39×10−10m2s−1 at 483K by semi-differential analysis in voltammogram. Moreover, the nucleation and the growth process of Nd(0) were evaluated from chronoamperometry at 473K. The result indicated that the nucleation mechanism of Nd nuclei altered from instantaneous to progressive nucleation when the induced overpotential became more negative than the peak potential of Nd(0) electrodeposition estimated from the voltammogram.

Diffusion of Nd in hcp Mg and interdiffusion coefficients in Mg–Nd system

Diffusion couple experiments for Mg–Nd system were performed to investigate the Nd diffusion in Mg solid solution and the interdiffusivities of intermediate phases. Experiments were conducted at 460, 480 and 500°C for 3, 4 and 3days respectively. Phase diagram data obtained from the diffusion couple experiments are consistent with previous experimental data and thermodynamic modeling. Impurity diffusion coefficient of Nd in Mg solid solution is almost three times of Gd and Y but lower than that of Al and Zn.

Diffusion of Nd and Mo in lanthanum tungsten oxide

Cation diffusion in functional oxides exposed to electrochemical gradients may lead to kinetic demixing or decomposition and, consequently, determine the life-time of the functional component. Here we present chemical diffusion coefficients of Nd and Mo in the mixed proton–electron conductor lanthanum tungsten oxide, La28−xW4+xO54+3x/2 (LWO), measured at 1000 to 1200°C in both oxidizing and reducing atmospheres. The bulk diffusivities of Nd and Mo were similar at all temperatures investigated and did not change significantly from oxidizing to reducing conditions. On these bases it is suggested that bulk diffusion of both Nd and Mo occurs via the La2 site on which both cations reside. Based on the low activation energy for bulk transport (~200kJ∙mol−1) at temperatures below 1200°C it is proposed that the cation defect concentrations are, in effect, frozen in. Preferential diffusion of Nd along the grain boundaries was rationalized based on space charge effects and depletion of W6+ and Mo6+ near the positively charged grain boundary core. Potential implications of kinetic demixing or decomposition of LWO membranes are also evaluated based on the present results.

Electrochemical analyses of diffusion behaviors and nucleation mechanisms for neodymium complexes in [DEME][TFSA] ionic liquid

ABSTRACT The electrochemical and nucleation behavior of Nd(III) in the ammonium-based ionic liquid (IL), N,N -diethyl- N -methyl- N -(2-methoxyethyl) ammonium bis(trifluoromethyl-sulfonyl) amide, [DEME] [TFSA], were investigated in this study. The cathodic reaction of Nd(III) [Nd(III) + 3e − → Nd(0)] was observed at −3.30 V vs. Ag/Ag(I) using cyclic voltammetry at 353 K. The diffusion coefficient of Nd(III) was estimated to be 1.35 ± 0.10 × 10 −13 m 2 s −1 at 353 K using semi-integral and semi-differential analyses. The initial process of Nd electrodeposition was also evaluated by chronoamperometry, indicating that the initial nucleation and growth of Nd on the Pt electrode occurred via instantaneous nucleation at −3.40 V. As the applied potential became more negative, the mechanism changed from instantaneous to progressive nucleation. The number density of Nd nuclei in the initial stage of nucleation decreased as the overpotential increased. Furthermore, the electrodeposition of Nd was carried out under the conditions of −3.40 V and −3.60 V at 353 K. SEM observations of the electrodeposits were consistent with the series of results obtained by chronoamperometry. The electrodeposits consisted mainly of Nd metal and oxide mixtures, whereas bonding with the light elements (C, F, and S) of the IL was suppressed, as demonstrated by EDX and XPS. The results suggested that sufficient dehydration and control of the water content of the electrolyte are important factors for obtaining metallic Nd with high purity.

Investigation on the electrochemical behavior of neodymium chloride at W, Al and Cd electrodes in molten LiCl-KCl eutectic

Electrochemical behavior of neodymium (III) ion was studied in LiCl-KCl eutectic melt in the temperature range 723-798K on inert tungsten electrode using various transient electrochemical techniques such as cyclic voltammetry, convolution voltammetry, chronopotentiometry and square wave voltammetry. The reduction of Nd(III) ion to Nd metal on tungsten electrode takes place in two steps- Nd(III)/Nd(II) and Nd(II)/Nd(0). The diffusion coefficient of Nd(III) and Nd (II) ions were determined. Reduction of Nd(III) to Nd(II) showed reversible electrode behavior and that for Nd(II) to Nd metal followed the quasi-reversible behavior. Heterogeneous rate constant for the reduction, Nd(II)/Nd(0) was estimated from the convoluted voltammograms. The apparent standard electrode potentials,ENd(III)/Nd(II)*, ENd(II)/Nd(0)* and ENd(III)/Nd(0)* were estimated from the cyclic voltammograms.The electrode behavior of Nd(III) ion on solid aluminium electrode and liquid cadmium electrode was studied by cyclic voltammetry. Under-potential reduction of Nd(III) ion takes place on Al and Cd cathodes in a single step with three electron transfer. The apparent standard electrode potentials, ENd(III)/Nd(Al)* and ENd(III)/Nd(Cd)* were estimated for different temperatures in the range 698-773K. The formation of intermetallics, Al11Nd3 and Cd11Nd were studied from open circuit potential measurement on Al and Cd film electrode respectively. The Gibbs energy of formation for these intermetallics was evaluated. The activity of neodymium in Al/Cd, the excess Gibbs energy and the activity coefficient of neodymium in Al/Cd were estimated from the open circuit potential measurement. SEM-EDX analysis and the XRD pattern of the electro-deposit revealed the formation of Al11Nd3 and Cd11Nd on Al and Cd cathodes respectively.

Attempts to the electrodeposition of Nd from ionic liquids at elevated temperatures

The suitability of triethyl-pentyl-phosphonium bis(trifluoromethyl-sulfonyl)amide ([P2225][TFSA]), room temperature ionic liquid for the electrodeposition of neodymium has been investigated in this study. From the standpoint of the scientific aspects, the temperature dependence of the reduction behavior for Nd(III) in [P2225][TFSA] was investigated from the cyclic voltammetry and the diffusion coefficient of Nd(III) was investigated by chronopotentiometry with cylindrically symmetrical diffusion. It was revealed that the over-potential of reduction reaction for Nd(III) was decreasing with elevating the bath temperatures and the diffusion coefficient of Nd(III) was estimated to the order of 10−11m2s−1 at 100°C. The activation energy of diffusion for Nd(III) obtained from the temperature dependence was 61kJmol−1. On the other hand, the spectroscopic and thermal analyses were also researched and it was revealed that the complex formation of Nd(III) in [P2225][TFSA] would not be rigid structure. The fusion temperature and the enthalpy of NdTFSA3 were estimated to be 195°C and 24kJmol−1, respectively.According to the electrochemical, spectroscopic and thermal evaluations, the electrodeposition of neodymium in [P2225][TFSA] was performed by potentiostatic electrolysis at −3.1V at 150°C in order to stimulate the mass transfer and to lower solution viscosity. The current efficiency evaluated from the mass change of the anode was more than 90%. A black electrodeposit on a copper substrate was fine and formed uniformly neodymium particle was observed by SEM. It was also identified that the contents of metallic neodymium in electrodeposits were 48% from the evaluation of EDX. The electrodeposit was composed of most of metallic neodymium and a part of neodymium oxide as identified from XPS.

Growth and thermal properties of Nd 3+:YbVO 4 crystal

New crystal Nd 3+:YbVO 4 has been successfully grown by using the Czochralski method. The rocking curves from (0 0 4) and (4 0 0) diffraction planes of as-grown Nd 3+:YbVO 4 crystal were measured by the high-resolution X-ray diffractometer (HRXRD) D5005, and the full-width values at half-maximum were 19.80″ for (0 0 4) face and 70.92″ for (4 0 0) face, respectively. The measured effective segregation coefficients were 0.545 for Nd 3+ and near 1 for V 3+ and Yb 3+ by using the X-ray fluorescence method. The density of Nd 3+:YbVO 4 crystal is also measured. The measured thermal expansion coefficients are α 1=2.6×10 −6 K –1, α 2=2.5×10 −6 K –1, α 3=8.7×10 −6 K –1 from 298.15 to 573.15 K along its crystallographic a, b and c axes, respectively. The measured specific heat is 0.45–0.65 J/g·K in the temperature range from 298.15 to 573.15 K. The thermal diffusion coefficients of Nd:YbVO 4 were measured and the thermal conductivities were also calculated.

Determination of Diffusion Coefficient of Nd<SUP>3+</SUP> in NdCrO<SUB>3</SUB> Based on Solid State Reaction

The solid state reaction, (1 /2 )Nd 2 O 3 + (1/2)Cr 2 O 3 → NdCrO 3 , was studied between 1473 K and 1773 K in air to determine the parabolic rate constant. The electrical conductivity of the NdCrO 3 phases separately equilibrated with Nd 2 O 3 and Cr 2 O 3 were measured between 1673 K and 1773 K in an argon-oxygen mixture. The standard Gibbs energy change for the solid state reaction was estimated from the activity dependence of the electrical conductivity of NdCrO 3 According to Wagner's theory, the diffusion coefficient of Nd 3+ in NdCrO 3 can be evaluated from the parabolic rate constant for the solid state reaction, the standard Gibbs energy change of the solid state reaction, and the defect equilibrium reaction in NdCrO 3 . From these data, the diffusion coefficient of Nd 3 in NdCrO 3 was given by D Ma3+ /m 2 s -1 = 1.3 × 10 -6 .exp(-343 kJ mol -1 /RT) (P O2 /Pa) 3/16 a 1/8 Cr2O3 where a Cr2O3 is the activity of Cr 2 O 3 and P O2 is the oxygen pressure. The obtained diffusion coefficient of Nd 3+ in NdCrO 3 was compared with that of Y 3+ in YCrO 3 and that of La 3+ in LaCrO 3 .

Liquid metal extraction of Nd from NdFeB magnet scrap

This research involves using molten magnesium (Mg) to remove neodymium (Nd) from NdFeB magnet scrap by diffusion. Mg was melted over pieces of NdFeB scrap and held at temperatures in the range 675–705 °C for 2–8 h. The Mg was allowed to solidify, and the castings were then sectioned and characterized using scanning electron microscopy, x-ray diffraction, and chemical analysis. Nd was found to have diffused out of the solid scrap into the molten Mg. The thickness of the diffusion layer was measured, the diffusion of Nd through the NdFeB scrap into liquid Mg was described, and the diffusion coefficient of Nd in liquid Mg was estimated.