Cause of gas emission during sintering of Nd–Fe–B magnets

The degassing of an Nd_14.5Fe_76.3Ti_1.4Al_1.1B_6.7 alloy (at %) has been studied. The cause for the degassing of the Nd–Fe–B material during its sintering is shown to be hydrogen evolution. At 250–550°C, hydrogen escapes from the Nd₂Fe₁₄B phase; at higher temperatures (700–900°C), hydrogen evolution from a Nd-rich phase takes place. The cause for hydrogen evolution consists in the decomposition of the Nd(OH)₃ neodymium hydroxide during fine milling. The decomposition of hydroxide results in the formation of the Nd₂O₃ neodymium oxide, which deteriorates the magnetic isolation of Nd₂Fe₁₄B-phase grains; this leads to an abrupt increase in the irreversible magnetization losses.     

Neodymium naphthenate-loaded organic phase stripping using sodium oxalate

Neodymium naphthenate-loaded organic phase stripping using sodium oxalate solution was studied to explore the feasibility of synchronous rare earth-loaded organic phase stripping, rare earth precipitation, and blank organic phase saponification. Experimental results show that loaded organic phase stripping, rare earth precipitation, and blank organic phase saponification can be realized simultaneously. When using 20% excess of sodium oxalate over the stoichiometry with the volume ratio of organic phase to aqueous phase of 1:1 at 25 °C for 40 min, the single stage stripping rate and saponification value are about 40% and 0.29 mol/L, respectively. After 16 stages of countercurrent continuous stripping, the stripping rate of neodymium can reach 99%, the saponification value is 0.42 mol/L, the Nd³⁺ concentration in saponified organic phase is less than 0.0020 mol/L, and the main phase in precipitation is Nd₂(C₂O₄)₃·10H₂O. Afterwards, this saponified organic phase can be used in the extraction of NdCl₃ solution, and then the loaded organic phases (neodymium naphthenate) with 0.16 mol/L Nd³⁺ can be retrieved. The morphology, particle size distribution, and composition of the Nd₂(C₂O₄)₃·10H₂O products are similar to those of the current direct precipitation products. The neodymium oxide prepared by continuous calcination of neodymium oxalate meets the national standard of China (GB/T 5240?2015). These results prove the feasibility of stripping neodymium naphthenate-loaded organic phase by using sodium oxalate solution. Sodium oxalate can serve as a stripping agent, a saponifier, and a precipitator, thereby simplifying rare earth extraction and separation. This study provides theoretical and technical support for the development of a novel method for rare earth extraction and separation.     

Enhanced separation of praseodymium and neodymium by kinetic“push and pull”system of[A336][NO_3]-DTPA in a column extractor

A new approach was suggested in present work for improving the separation between Pr(Ⅲ) and Nd(Ⅲ)by a so-called kinetic "push and pull" system consisting of [A336][NO_3] and DTPA in a column extractor.It is revealed that,when organic extractant [A336][NO_3] is continuously pumped into the column extractor in the form of dispersed oil droplets and at the same time DTPA was injected into the aqueous feed solution whet the extraction was just started,the separatiot factor of Pr(Ⅲ) to Nd(Ⅲ),βPr/Nd,increased obviously with the time,and could even achieve 21.7.Such an amazing increase in β_(Pr)/Nd value might be due to the extraction rate of Pr(Ⅲ) by [A336][NO_3] oil droplets being faster than that of Nd(Ⅲ),while the complexing rate of Nd(Ⅲ) with DTPA in the aqueous solutions being faster than that of Pr(III).The opposite order of the two rates for Pr(Ⅲ) and Nd(Ⅲ) result in their kinetic "push and pull" separation.In contrast,the β_(Pr)/Nd value in traditional thermodynamic separation reported in previous literatures is only around 5 or even less,even though using the same extractant [A336][NO3] and DTPA but by previously adding DTPA into the aqueous feed solutions for pre-complexing of Pr(Ⅲ) and Nd(Ⅲ).Various effects from the pH and addition amount of DTPA aqueous solutions,LiNO_3 concentrations in initial aqueous feed solutions,the initial concentration ratios of Pr(Ⅲ) to Nd(Ⅲ) ions,the initial pH of aqueous feed solutions,and the concentrations of [A336][NO_3] in organic phases,on the kinetic separatiot of Pr(Ⅲ) and Nd(Ⅲ) are discussed.The present work highlights a promising approach for separation of rare earths or other targets with extreme similarity in physicochemical properties.     

Structural characterization of Nd-doped in silica host matrix prepared by wet chemical process

Silica host matrix containing neodymium which is potentially important for the formation of nanocrystalline metal oxides was prepared by solgel method, using tetra-ethoxysilane and Nd(NO₃)₃ as precursor materials. The prepared samples were changed from amorphous to nanocrystallites phase at sintered temperature 550 °C (4 h), 750 °C (8 h) and 950 °C (12 h). The thermally treated sample microstructures were investigated using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). While a further increase of the temperature at 750 °C and annealing time (8 h) resulted in the formation of cubic and hexagonal Nd₂O₃ nanocrystallites. At constant sintering temperature 950 °C for 12 h, the samples showed sharper and intense peaks. The sizes of Nd₂O₃ nanocrystallites were characterized by XRD with average size ～46 nm.     

Investigation of the structure of neodymium-di-(2-ethylhexyl) phosphoric acid combinations using electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry and nuclear magnetic resonance spectroscopy

Neodymium-di-(2-ethylhexyl) phosphoric acid (DEHPA) species forming in the organic phase during solvent extraction of neodymium with solutions of DEHPA have been studied. Two samples were prepared: one with a low molar ratio of neodymium to DEHPA, which is liquid and clear, and the other with a high molar ratio of neodymium to DEHPA (complete loading), which has the consistency of a gel. Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric investigations show numerous compounds, in addition to the generally assumed species dimeric DEHPA and Nd(DEHP-DEHPA)₃, in the liquid sample. The nuclear magnetic resonance (NMR) spectroscopic investigation of pure DEHPA and of completely loaded sample confirm the formula of pure DEHPA and of the organic part of Nd(DEHP)₃. Furthermore, chemical analysis of a dried, completely loaded sample also proves the existence of the species Nd(DEHP)₃. Results of X-ray powder diffraction measurements of this sample agree well with literature data.     

Effects of precipitates on grain size and mechanical properties of AZ31-x% Nd magnesium alloy

The effects of precipitates on grain size and mechanical properties of as-cast AZ3 1-x%Nd magnesium alloy were investi- gated, and the affecting mechanism was also discussed. The results indicated that Al2Nd phase, AlllNd3 phase and a few AI-Mn-Nd-Fe phase were furmed when adding 0.38 wt.%-1.46 wt.% Nd into AZ31 melt, coarse AI2Nd transformed into Al11Nd3 gradually with the increasing of Nd content. Due to structure and size transformation and content increasing of AI-Nd phase, the grain size of AZ31-x% Nd alloy increased firstly, and then decreased with the increment of Nd content. After reaching a minimum value, once again it rose up, provided that Nd content was further increased. The tensile property reached its optimal value when the adding amount of Nd content was 1.05 wl.%, however, adding excessive amount of Nd deteriorated both ultimate strength and elongation ofAZ31 alloy.     

Corrosion of 12Kh18N10T Steel in the LiCl–KCl–<Emphasis Type="Italic">n</Emphasis>NdCl<Subscript>3</Subscript> Melt

The high-temperature corrosion of a 12Kh18N10T steel in the melt of lithium and potassium chlorides and neodymium trichlorides is investigated at a temperature of 773 K. The NdCl₃ concentration is varied from 0.2 to 5 mol %. In this study, neodymium is an analog of uranium. The composition of the electrolyte is close to the composition of the electrolytes used for processing nitride spent nuclear fuel (SNF). The main investigation technique is gravimetry, which includes aging of the steel in the melt for 1–24 h. Atomic absorption and electron microprobe analyses are also used.     

Synthesis and spectral properties of Nd-doped glass-ceramics in SiO2-CaO-MgO system prepared by sol-gel method

SiO2-CaO-MgO glass and glass-ceramic powder doped with Nd3+ were synthesized with sol-gel method.Tetraethylorthosilicate (TEOS),Ca(NO3)2·4H2O,Mg(NO3)2·6H2O,Nd(NO3)3·6H2O,ethanol,distilled water,and HNO3 were used as starting materials.The synthesized powder’s properties were examined with simultaneous thermal analysis (STA),X-ray diffraction (XRD),photoluminescence (PL) and scanning electron microscopy (SEM) analysis.The STA curves showed that the softening point and crystallization temperatures were shifted to higher temperatures with increasing dopant content.Regarding XRD patterns of glass samples,Nd was found to act as an intermediate oxide in glass matrix.The XRD patterns of glass-ceramic samples indicated that bredigite and akermanite crystallized in the glass matrix after heat treating at 900 oC.The fluorescence spectra showed that glass-ceramics emitted much stronger irradiation than glasses with the same dopant content.The SEM images illustrated uniform and homogeneous distribution of applied oxides in glass and glass-ceramic compositions.     

A molten salt process for producing neodymium and neodymium-iron alloys

The production of low-cost neodymium metal in a stirred tank reactor by the reduction of Nd₂O₃ with sodium in the presence of CaCl₂−KCl−NaCl melts by the overall reaction Nd₂O₃+3CaCl₂+6Na→2Nd+3CaO+6NaCl at ∼750 °C is described. The metal produced is recovered from the salt medium by dissolving it in a Nd−Zn or Nd−Fe alloy pool. In the case of Nd−Zn alloy pools, product yields (percentages of theoretical neodymium produced) in excess of 94 pct are obtained when using salt ratios,i.e., the amounts of salt per gram of neodymium produced, ≥3.5 and excess reductant ≥10 pct. The alloy produced is of high quality, and following vacuum distillation of the zinc, can be used in producing General Motors’ MAGNEQUENCH alloy for permanent magnets. In the case of Nd−Fe pools, the yield is also ∼95 pct with a salt ratio as low as 3.5. The yield is found to depend on the salt composition and salt ratio, and to decrease at salt ratios below 3.25. Stirrer position has little effect on yield, while increasing the temperature and placing fins in the reactor increase the yield. The Nd−Fe alloy produced is of as good quality as that produced using Ca reductant and is suitable for direct use in preparing the MAGNEQUENCH alloy.     

Solubilities and raman spectra of NdOCl in some chloride melts of interest for the electrowinning of magnesium from its oxide

Some fundamental data related to the solvent proposed for a new technical electrolytic process for magnesium production based on MgO as the raw material are presented. Liquidus data are obtained for MgCl₂-rich melts in the MgCl₂-NdOCl system. The solubility of MgO and NdOCl in pure liquid NdCl₃, MgO in NdCl₃-MgCl₂ and in MgCl₂-NdCl₃-NaCl liquid mixtures, and NdOCl in CaCl₂ and Cs₂MgCl₄ have also been studied. The solubility of MgO decreases when MgCl₂ is added to the pure NdCl₃ and further by additions of NaCl as expected. A so far unidentified compound having the composition Mg _x Nd _y OCl_2x-3y-2 where x and y are larger than 1 seems to be formed in very small amounts in these melts. This compound seems to precipitate at temperatures higher than 910 °C in the NdCl₃-MgO quasi-binary system containing about 8 mol pct MgO and seems to remain suspended in the melt in small quantities. The first liquid-solid phase transition observed, however, was the NdCl₃ (1)=NdCl₃ (s) transition <758 °C. X-ray diffraction (XRD) data of filtered samples of this solid show new X-ray lines not detected in MgCl₂, NdCl₃, NaCl, MgO, and NdOCl. The published phase diagram of the quasi binary system MgCl₂-NdOCl is, according to the present work, not correct because the solubility of MgO seems to be much less than previously reported. Raman spectroscopic data of NdCl₃-MgCl₂-NdOCl melts show the known features of the NdCl₃-MgCl₂ and NdCl₃-NdOCl melts. Raman bands due to dissolved species of the unidentified compound were not detected. In view of the obvious small concentration of this species in the liquid phase, this was reasonable. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

Preparation of Nd_2O_3 nanorods in SDBS micelle system

Well-crystallized Nd2O3 nanorods were prepared in the aqueous solution containing neodymium nitrate, sodium hydroxide（dissolved in ethanol） and sodium dodecyl benzene sulfonate（SDBS）. One dimensional nanorods of neodymium hydroxide were synthesized first, which was then placed at different temperatures（600 and 800 ℃） in a calcar for 10 h to form Nd2O3 nanorods. The morphology and crystal structure of the products were investigated by X-ray diffraction, transmission electron microscopy, field emission transmission electron microscopy, Fourier transform infrared spectroscopy and fluorescence spectrometry. By using SDBS micelles as a template, this method manufactured uniform morphology of hexagonal one-dimensional neodymium oxide nanorods with a diameter ranging from 20 to 70 nm. The length of the nanorods increased with prolonged reaction time.     

Synthesis and Spectral Properties of Nd^3＋： Gd3Ga5O12 Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.     

Phase Equilibria in the Nd ― Re ― B System

XRD has been applied to component interaction in the Nd ― Re ― B system. Isothermal sections have been constructed for the phase diagram at 600°C (a region >33 at.% boron) and 800°C (>33 at.% boron). It is confirmed that it contains the previously known borides Nd₂Re₃B₆ (Pr₂Re₃B₆ structure type) and Nd₈Re_{13 − x} B₁₂ (Pr₈Re_{13 − x} B₁₂ structure type). Two new ternary compounds are reported: ∼NdRe₄B₄ considered to have a tetragonal incommensurate structure and ∼Nd₅Re₂B₆, whose structure is unknown.

     

Synthesis,characterization and thermolysis of lanthanide metal nitrate complexes with 1, 10-phenanthroline,Part-95

The nitrate complexes of cerium, praseodymium and neodymium with 1,10-phenanthroline(phen) of general formula [Ln(phen)2(NO3)2(H2O)2]·NO3(where, Ln=Ce, Pr and Nd) were prepared and characterized by X-ray crystallography. Thermolysis of these complexes was investigated by simultaneous thermogravimetry(TG) and differential thermal analysis(DTA). Isothermal TG was taken to evaluate the kinetic parameters using model fitting as well as model free isoconversional methods. The thermolytic pathways were also suggested, which involves decomposition followed by ignition. All the three complexes had coordination number ten and showed multistep decompositions. In order to evaluate the response of rapid heating, ignition delay(Di) measurements were undertaken. The activation energies for ignition were found to decrease in the order: NdPrCe.     

On some rare-earth germanides

Conclusions We have studied the conditions for obtaining the germanide phases Me₅Ge₃, MeGe, and MeGe₂ for lanthanum, cerium, praseodymium, and neodymium by arc melting in argon.The optimal ratios of the initial components have been established. To obtain digermanides of lanthanum, cerium, and praseodymium we must have a 1% excess of germanium in the initial mixture; to obtain neodymium germanides the initial mixture must have a deficit of 1–3% of Nd₅Ge₃ and NdGe₂ and 1–5% for NdGe.The pyconometric densities and microhardnesses of the germanides have been measured.Translated from Poroshkovaya Metallurgiya, No. 11 (59), pp. 92–96, November, 1967.     

Thermal conductivity of NdCl<Subscript>3</Subscript>-<Emphasis Type="Italic">M</Emphasis>Cl (<Emphasis Type="Italic">M</Emphasis> = Na,K, Cs) melts

The thermal conductivities of individual NdCl₃, the K₃NdCl₆ chemical compound, an equimolar 0.5NdCl₃-0.5NaCl mixture, and eutectic 0.5NdCl₃-0.5KCl and 0.45NdCl₃-0.55CsCl mixtures are measured. For all melts, the concentration and temperature dependences of the thermal conductivity are found.     

Preparation of Nd(III) carbonate by precipitation stripping of Nd(III)-loaded VA10

The preparation of fine particles of Nd(III) carbonate from kerosene solution, from which Nd(III) was extracted with versatic acid 10 (VA10) by a precipitation stripping technique using an aqueous NH₃-(NH₄)₂CO₃ solution as stripping medium, was studied. In preliminary experiments, we were unable to recover simple Nd(III) carbonate from Nd(III)-loaded VA10 by CO₂ gas bubbling, when water, (NH₄)₂CO₃, NH₄HCO₃, NaHCO₃, or NA₂CO₃ solution saturated with CO₂ was used as the stripping solution. To obtain simple Nd(III) carbonate, it is necessary to use more than the stoichiometric amount of NH₃ compared to VA10 and about 10 times as much (NH₄)₂CO₃ as Nd(III). The solution mixture of NH₃-(NH₄)₂)CO₃ acts as a pH buffer, an adductor for VA10, and a CO ₃ ²⁻ ion source. Although it was concluded that the precipitates are Nd₂(CO₃)₃·xH₂O (x⊧4), their X-ray pattern does not coincide with that quoted by JCPDS. By heating these precipitates, cubic Nd₂O₃ was obtained at 823 K, while, at 973 K, hexagonal Nd₂O₃ was formed. Since the stripping solution consisting of NH₃-(NH₄)₂CO₃ was highly alkaline, VA10 was also stripped in the aqueous phase. To use a closed-circuit system for the precipitation stripping of Nd(III) carbonate from Nd(III)-loaded VA10, it is important to regenerate VA10 in the organic phase. For this purpose, evaporation of NH₃ by air bubbling was studied. By bubbling air into a stripping solution warmed at 333 K, almost all the VA10 can be transferred to the organic phase.     

Extraction mechanism and separation behaviors of low-concentration Nd3+ and Al3+ in P507–H2SO4 system

In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore, the extraction mechanism and separation behaviors of Nd³⁺ and Al³⁺ in the Nd₂(SO₄)₃–Al₂(SO₄)₃ mixed solution using P507 were studied in this work. The extraction of Nd³⁺ and Al³⁺ follows the cation exchange mechanism. With the increase of the equilibrium pH, β_Nd/Al in the extraction of the Nd₂(SO₄)₃–Al₂(SO₄)₃ mixed solution using P507 is always higher than that in the extraction of single Nd₂(SO₄)₃ and Al₂(SO₄)₃ solutions. It can be attributed to the fact that the extraction of Nd³⁺ using P507 is much faster than that of Al³⁺, and Al³⁺ is more prone to be hydrolyzed at lower pH. β_Nd/Al in the extraction of the Nd₂(SO₄)₃–Al₂(SO₄)₃ mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5–1.9. The extraction of Nd³⁺ using P507 is much faster than that of Al³⁺, but the stability of Al³⁺-loaded organic phase is better than that of Nd³⁺-loaded organic phase, thus Nd³⁺ in the Nd³⁺-loaded organic phase is gradually replaced by Al³⁺ in the aqueous phase with the increase of mixing time.     

Unique structural and magnetic traits of Nd3+-substituted Co–Zn nanoferrites

Because of the technological potential of magnetic spinel nanoferrites, we prepared neodymium ion (Nd³⁺)-substituted cobalt-zinc ferrites (CZFs) with the form Co_0.5Zn_0.5Nd_xFe_2–xO₄ (0.0 ≤ x ≤ 0.05) via a hydrothermal method. The as-prepared samples were thoroughly characterized using various analytical techniques. XRD, FTIR and FESEM analyses confirm the formation of a cubic spinel phase of the CZFNPs (CZF nanoparticles). A decrease in the lattice parameter due to the substitution of Fe³⁺ by Nd³⁺ in the lattice structures is manifested in the XRD refinement data. The magnetic properties of the proposed CZFNPs were evaluated in terms of the saturation magnetization, remanence, coercivity, squareness ratio and magnetic moment. These CZFNPs exhibit superparamagnetic behaviors at room temperature. Moreover, the Nd³⁺ inclusion does not significantly affect the measured magnetizations and coercivities of the CZFNPs. Samples containing 0.01 and 0.03 Nd³⁺ exhibit lower saturation magnetizations than that of the pristine product. The squareness ratios much less than 0.53 are ascribed to surface spin disordering. The unique magnetic traits of the synthesized CZFNPs are primarily attributed to the substitution of Fe³⁺ ions, with smaller ionic radii, by Nd³⁺ ions, with larger ionic radii. The proposed CZFNPs may be useful for diverse magneto-optic applications.     

Optical properties and Judd–Ofelt analysis of Nd2O3 nanocrystals embedded in polymethyl methacrylate

PMMA matrices were doped with nano-crystalline neodymium oxides synthesized by thermal decomposition process. X-ray diffraction and high-resolution transmission electron microscopy measurements were carried out to investigate the structure, phase, and the morphology of the Nd_2O_3 nanocrystals and those embedded in the PMMA matrix. The average grain sizes were estimated 35 ± 6 nm and 46 ± 4 nm for non-annealed and annealed Nd_2O_3 particles, respectively. The grain size distributions(GSD) were calculated from the diffraction peaks of the annealed and non-annealed Nd_2O_3 powders and doped PMMA samples. The mass density, refractive index. UV-Visible absorption spectra were measured and the data were analyzed using the Judd-Ofelt approach to determine the oscillator strengths, the spontaneous emission probabilities and the branching ratios as a function of the nano-crystalline Nd_2O_3 content in the range of 0.1 wt.%-20 wt.% of MMA. Luminescence spectra upon 808 nm diode laser excitation were carried out in the wavelength range of 850-1550 nm at room temperature. The photoluminescence study has shown that the reasonably sharp emission peaks were observed upon heat treatment at 800 ℃ for 24 h for all concentrations of Nd_2O_3 nanopowders in PMMA. The infrared laser transition of Nd~(3+) ions at about 1.06 μm due to the ~4F_(3/2)→~4I_(11/2) transition was analyzed and discussed in Nd_2O_3 system for their possible applications in the photonic technology.