First Principles Study of Uranium Solubility in Gd2Zr2O7 Pyrochlore

Ab initio calculation is performed to investigate the uranium solubility in different sites of Gd₂Zr₂O₇ pyrochlore. The Gd₂Zr₂O₇ maintains its pyrochlore structure at low uranium dopant levels, and the lattice constants of Gd₂(Zr_{2-y}U_y)O₇ and (Gd_{2-y}Uy)Zr₂O₇ are gen-erally expressed as being linearly related to the uranium content y. Uranium is found to be a preferable substitute for the B-site gadolinium atoms in cation-disordered Gd₂Zr₂O₇ (where gadolinium and zirconium atoms are swapped) over the A-site gadolinium atoms in orderedGd₂Zr₂O₇ due to the lower total energy of (Gd_{2-y}Zr_y)(Zr_{2-y}U_y)O₇.     

Magnetic properties of complex oxides Gd2SrM2O7 (M = Fe, Al)

Magnetic susceptibility of complex perovskite-like oxides Gd₂SrFe₂O₇ and Gd₂SrAl₂O₇ was studied. A sharp decrease in the magnetic characteristics of gadolinium ferrite as compared to gadolinium aluminate points to the presence of strong antiferromagnetic interactions between the iron ions.     

Characterization and luminescence properties of Gd2O3 phosphor

Gd₂O₃ phosphor was synthesized by combustion synthesis using gadolinium nitrate hexahydrate as precursor and urea as fuel. Structural and surface morphology were studied by X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Chemical composition analysis of the phosphor was performed by Fourier-transform infrared spectroscopy, and tts optical properties were characterized by use of photoluminescence (PL) and thermoluminescence (TL) techniques. In PL spectra, feeble emission at 490 nm (blue) and intense emission at approximately 545 nm (green) are observed after excitation at 300 nm. TL measurement was performed on the Gd₂O₃ phosphor by irradiating it with γ-rays (1 kGy). A well resolved glow peak at 226.4 °C was observed. Kinetic data were estimated from the TL glow curve by use of Chen’s peak-shape method; the results are discussed in detail. The average particle size of the Gd₂O₃ phosphor was 41 nm; a monoclinic phase was formed at a firing temperature of 500 °C. This was in agreement with SEM and TEM results.     

Étude par spectrométrie infra-rouge des complexes des terres rares avec l'oxyde de tri-n-butylphosphine á l'état solide

Tri-n-butylphosphine oxide (TBPO) reacts with rare earth nitrates to form complexes of general formula Me(NO₃)₃·3 TBPO. These complexes were studied by infrared spectrometry. The coordination of the nitrates is not the same along the lanthanide series. They are bidentate for the light rare earths and monodentate for the heavy earths. The P=O frequency does not vary monotonously when Z increases; there is a break for gadolinium. This is explained by an influence of backbonding, the decrease of the ionic radius and the coordination number.     

Microstructural Characteristics and Magnetic Properties of Gadolinium-Substituted Cobalt Ferrite Nanocrystals Synthesized by Hydrothermal Processing

Gadolinium substituted cobalt ferrite nanocrystals with composition of CoFe_2?xGd_xO₄ (x = 0–0.04 in a step of 0.01) were prepared by a hydrothermal process and without subsequent annealing. X-ray diffraction, field-emission scanning electron microscopy, and vibrating sample magnetometer were used to investigate the effect of Gd³⁺ cation substitution on structural Characteristics and magnetic properties of cobalt ferrite nanocrystals. The X-ray diffraction analysis demonstrated that single phase spinel ferrites were obtained. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, more important, different shapes. The results of magnetic hysteresis at a room temperature showed that with an increase in gadolinium content, the coercive field decreased from 1250 Oe for x = 0 to 450 Oe for x = 0.03. In addition, it was observed that with substitutions of gadolinium cations, the values of saturation magnetization decreased.     

Study of the gadolinium sorption on the C100 ion-exchange resin for the development of the antineutrino detector targets

Adsorption of the gadolinium from H₂O and HCl solutions on the ion-exchange resin C100 is investigated. The experiments were carried out by varying the acidity of the liquid phase, the amount of sorbent, and the temperature. The maximal sorption of the ions Gd³⁺ is observed from the solution 0–0.2 M HCl under optimal conditions, the sorption reaches more than 99.5%. Sorption of Gd³⁺ on C100 from H₂O solution occurs most intensively during the first 3 min then for 30 min the system smoothly comes to equilibrium. The maximal sorption capacity of the resin C100 amounted to 1.2 ± 0.1 mmol g^?1. The thermodynamic parameters of sorption: ΔG = ? 24.20 kJ mol^?1, ΔS = ? 90.27 J mol^?1 K^?1, ?H = ? 50.93 kJ mol^?1 were evaluated. It is shown that the sorption of gadolinium on the ion-exchange resin C100 is described by models of kinetically pseudo-first and pseudo-second order. It is established that the Gd³⁺ sorption on the C100 resin is reversible second order chemical reaction.     

多壁碳纳米管对稀土元素的吸附性能

研究了改性多壁碳纳米管(MWCNTs)对稀土元素的吸附。 采用硝酸、次氯酸钠、过氧化氢、高锰酸钾4种方法对MWCNTs进行改性,考察了改性MWCNTs对稀土元素的吸附能力。 采用紫外-可见分光光度法测定稀土元素的浓度,比较了未处理和不同方法处理的MWCNTs对稀土元素的吸附能力。实验结果表明,NaClO改性的MWCNTs对稀土元素的吸附能力最强。以稀土元素钐(Sm)、钆(Gd)、镱(Yb)为代表,研究了NaClO改性MWCNTs对稀土元素的吸附性能。 考察了溶液pH值、离子强度、吸附剂用量、温度等因素对吸附性能的影响。当溶液pH值在2~7范围内,NaClO改性的MWCNTs对Sm、Gd、Yb的吸附随pH值增大而增强。 当离子强度和MWCNTs的用量增大时,对稀土元素的吸附能力降低。3种元素在NaClO改性的MWCNTs上的吸附均为放热过程,其反应焓变ΔH分别为：-6.44、-5.63和8.31 kJ/mol。吸附等温线符合Langmuir和Freundlich等温吸附方程。     

Magnetostructural correlation for the Gd complexes with bridging oxygen

The dependence between the energy of magnetic exchange interaction J _Gd-Gd′ and the distance between gadolinium atoms in the binuclear structure D _Gd...Gd′ was constructed on the basis of our and literature experimental data for 34 gadolinium complexes with the [Gd₂O₂] core. The character of the established dependence is similar to the Bethe-Slater curve. The obtained correlation indicates the possibility to predict the character of interaction in the Gd complexes built of binuclear fragments with the [Gd₂O₂] core depending on the single parameter, namely, distance D _Gd...Gd′. The validity of this correlation was tested using as examples four binuclear gadolinium complexes obtained by the authors.     

Phase stability study of the pseudobinary system Gd2O2CO3–Nd2O2CO3 (420 °C ≤ T ≤ 850 °C, P = 1 atm. CO2)

Hexagonal as well as tetragonal rare earth oxycarbonates can act as hosts for optically active ions; hence, the knowledge of the structural modifications occurring when foreign hosts are inserted into the parent compound is of fundamental importance for the design of new phosphors. In this article, a phase stability study of the pseudobinary system Gd₂O₂CO₃–Nd₂O₂CO₃ at P = 1 atm. CO₂ between 420 and 850 °C is presented, to study the amplitude of the existence fields of the different structures typical of rare earth oxycarbonates. The samples were prepared by thermal decomposition of the corresponding oxalates in CO₂ atmosphere. According to composition and temperature, all the three structural forms reported for oxycarbonates (hexagonal, tetragonal, and monoclinic) have been observed. Above a certain temperature, that depends on composition and increases with Nd amount, all the samples decompose into the corresponding Gd–Nd-mixed oxides and crystallize into one of the three possible structural forms typical of rare earth sesquioxides. Structural refinements performed on the hexagonal oxycarbonates demonstrate that the insertion of Nd³⁺ in Gd₂O₂CO₃ results in a linear increase of the lattice parameters (Vegard’s law) and in a reorganization of the distances between and in the CO ₃ ^2? groups and the (Nd/Gd₂O₂)²⁺ layers.     

A new material in the nuclear technology: gadolinium zirconate pyrochlore prepared by reactive sintering

The ability of gadolinium zirconate pyrochlore for actinides incorporation in its lattice makes this material a possible matrix for the immobilization of nuclear wastes. The aim of the presented work was to develop a novel method of gadolinium zirconate synthesis by using a reactive sintering procedure under high pressure based on commercial ZrO₂ and Gd₂O₃ nanopowders. Samples were analyzed using X-ray diffraction and SEM to check their phase composition and microstructure. The obtained sintered pellets demonstrated peaks characteristic for pyrochlore structure for a wide range of preparation temperatures and high density (99.5 % of the theoretical value). It was found that the resulting materials exhibited a homogeneous microstructure and the average grain size dependent on sintering temperature.     

Re-investigations of thermal decomposition of gadolinium sulfate octahydrate

The crystals of Gd₂(SO₄)₃·8H₂O were obtained by slow crystallization from a saturated solution previously received by dissolving Gd₂O₃ in an aqueous solution of sulfuric acid. The thermal behavior of this salt was studied using simultaneous DTA–TG technique under a nitrogen and air, in the temperature range of 298–1773 K. It was found that the dehydration of gadolinium sulfate octahydrate as well as thermal decomposition of anhydrous Gd₂(SO₄)₃ undergo in two steps. The existence of two polymorphic modification of anhydrous gadolinium sulfate has been confirmed. The new XRD data for high-temperature polymorph of Gd₂(SO₄)₃ were given. All intermediate products of dehydration and thermal decomposition were characterized by EPR method.     

Preliminary investigation for the development of surrogate debris from nuclear detonations in marine-urban environments

The effect of ambient gas on measurements with microwave-assisted laser-induced plasma in microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS) was studied with relevance for the analysis of nuclear fuel. A pelletized gadolinium oxide (Gd₂O₃) sample, which was used as a simulated nuclear fuel, was irradiated by a pulsed Nd:YAG laser (532 nm, 5 mJ) coupled with microwaves (2.45 GHz, 400 W) under various gases of air, Ar, and He. Microwaves can be effectively used to enhance laser-induced plasma emissions. The emission spectrums of Gd obtained by MA-LIBS in Ar and He gases are much better than those of the air case. Namely, the spectral lines can be clearly identified and are far from molecular bands. Furthermore, the emission intensity is highest with low background emissions. Linear calibration curves of Ca in the concentration range between 0 and 500 mg/kg as an impurity in Gd₂O₃ have been successfully obtained in all gases. The detection limits of Ca impurity in air, Ar and He gases were 2, 0.8 and 0.6 mg/kg, respectively, which are much lower than the required limits of Ca impurity in nuclear fuels.     

The Effect of Chromium Oxide on the Conductivity of Ce<Subscript>0.9</Subscript>Gd<Subscript>0.1</Subscript>O<Subscript>2</Subscript>, a Solid-Oxide Fuel Cell Electrolyte

To study the effect of chromium oxide on the electric properties of Ce_0.9Gd_0.1O₂, a solid-oxide fuel cell electrolyte, two approaches were used: (a) the studying of electrochemical properties of the Ce_0.9Gd_0.1O₂- electrolyte after the spontaneous adsorption of chromium-containing molecules from a gas phase and (b) the analyzing of transport properties of the Ce_0.9Gd_0.1O₂-based chromium-containing compositions obtained by the mixing of solid-oxide electrolyte with chromium(III) oxide. It was found that the chromium reduction at the electrolyte surface dominates when chromium is adsorbed from gas phase. Both approaches allow concluding that the chromium presence in Ce_0.9Gd_0.1O₂ deteriorates the electrolyte transport properties at temperatures above 735°С. This is caused by the chromium incorporation into the electrolyte’s fluorite structure, as well as surface microheterogeneity induced by the chromium presence at the Ce_0.9Gd_0.1O₂ surface and the cerium and gadolinium cation redistribution between the grains’ bulk and surface. At intermediate temperatures (below 735°С) the electric conductivity of the Ce_0.9Gd_0.1O₂-based chromium-containing composition exceeds that of the initial solid-oxide electrolyte, which can be due to changes in transport properties of the chromium-containing phases formed at the Ce_0.9Gd_0.1O₂ surface and grain boundaries.     

Extraction equilibria of rare earths by a new reagent (2-ethylhexyl-3-pentadecylphenyl) phosphoric acid

A new reagent (2-ethylhexyl-3-pentadecylphenyl) phosphoric acid (EPPA = HR) was synthesized from cardanol (I, 37300-39-5) and was used to investigate the extraction behaviour of lanthanum(III), europium(III) and lutetium(III) from hydrochloric acid solutions. The species extracted were found to be Ln(HR(2))(3) (where Ln = La(III) or Eu(III) or Lu(III)). The extraction behaviour of the above lanthanides has also been compared with yttrium and other rare earths. It was observed that the extraction increases with increase in atomic number of rare earths. In addition, the extraction efficiency of EPPA has also been compared with well known acidic organophosphorus extractants like di-2-ethylhexyl phosphoric acid (DEHPA), 2-ethylhexyl-mono-2-ethylhexyl phosphoric acid (EHEHPA).     

Electrode Processes in a Eutectic KCl–KF Melt Containing Gadolinium Oxide

The electroreduction of gadolinium from a eutectic KCl–KF melt containing 0.210–1.233 wt % Gd₂O₃ on molybdenum and glassy carbon electrodes is studied at 1008 K. The solubility of gadolinium oxide is determined. It is shown that the reduction of a gadolinium oxyfluoride complex proceeds reversibly, with a subsequent reversible chemical reaction. The gadolinium reduction on an iron electrode in a eutectic KCl–KF melt purified of unwanted oxide ion impurities yields an iron-gadolinium alloy.     

Systematic Study of the Interaction Between VIV Centres and LnIII Ions in Well Defined {V 2 IV LnIII}{AsIIIW9O33}2 Sandwich-Type Clusters: Part 2

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK₆Gd_0.33 [((VO)₂Gd(H₂O)₄K₂(H₂O)₂(Na)(H₂O)₂)(α-B-AsW₉O₃₃)₂]·24H₂O (1) was prepared from acidified aqueous solutions of Na₂WO₄·2H₂O, As₂O₃ and VOSO₄·5H₂O to which Gd³⁺ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P2₁/m) shows that the anion consists of two [α-B-As^IIIW₉O₃₃]^9? trilacunary Keggin-type units linked by two VO²⁺, one Gd³⁺ as well as weakly by two K⁺ and one Na⁺ ions, resulting in a sandwich-type structure with idealized C _2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J _VV = ?2.55 cm^?1 (anti-ferromagnetic) between the vanadium ions and J _GdV = 0.6 cm^?1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na⁺ sites in the counter-cation–water system by Gd³⁺ ions (0.33 Gd³⁺ ions in total).     

The local structure of gadolinium vanadate–tellurate glasses and glass ceramics: Te2V2O9 crystalline phase

Glasses in the system xGd₂O₃ · (100 − x)[0.7TeO₂ · 0.3V₂O₅] with 0 ≤ x ≤20 mol% have been prepared from melt quenching method. Influence of gadolinium ions on structural behavior in vanadate–tellurate glasses has been investigated using FTIR spectroscopy, X-ray diffraction (XRD), and magnetic susceptibility measurements. The structural changes have been analyzed with increasing rare earth concentration. The structural changes, as recognized by analyzing band shapes of XRD and FTIR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as 20 mol%. The structure of the heat-treated glasses was found to consist mainly of the Te₂V₂O₉ crystalline phase. These vitreous systems were investigated by magnetic susceptibility measurements. From the paramagnetic susceptibility χ was calculated at different temperature and from the 1/χ(T) graph, the Curie temperature of the glass has been evaluated. Magnetic susceptibility data show the presence of small antiferromagnetic interactions between the Gd⁺³ ions.     

Computerized modeling of intermediate compounds formed during thermal decomposition of gadolinium nitrate hydrate

It was shown that after partial dehydration occurs a simultaneous condensation of four mol of initial monomer Gd(NO₃)₃ · 6H₂O into a tetramer Gd₄O₄(NO₃)₄. The heterocycle containing 4 gadolinium atoms gradually loses N₂O₅ and, through the formation of unstable oxynitrates, is transformed into Gd₂O₃. The interatomic distances and angles were calculated using the molecular mechanics method. The comparison of the potential energies of consecutive oxyphosphates permitted an evaluation of their stability. The models of intermediate oxynitrates represent a reasonably good approximation to the real structures and a proper interpretation of experimental data.     

Features of the sol-gel process of formation of nanostructured gadolinium oxide

The process of dehydration of Gd(OH)₃·nH₂O obtained by the sol-gel method from a solution of Gd(NO₃)₃, to Gd₂O₃ in the temperature range of 50–700°C was explored. The hydrogel and Gd₂O₃ structurization is shown to depend on the additives (AF-12 and 2-propanol). The final average particle size of Gd₂O₃ after annealing at 700°C is 20±2 nm, depending on the conditions of the synthesis. The resulting oxide particles are larger than the particles of yttrium oxide Y₂O₃ (17±2) obtained under the same conditions of the process due to the higher basicity of gadolinium and its higher coordination number with respect to the OH groups. This promotes the formation of crystalline phases of Gd(OH)₃ at lower temperature, 50–250°C, while maintaining a favorable structural short-range order in passing through an amorphous state to a crystalline Gd₂O₃.     

Counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) using tris-2-ethyl hexyl phosphate (TEHP)

Evaluation of tris-2-ethyl hexyl phosphate (TEHP) for counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) from nitric acid medium was carried out under wide experimental conditions. Batch extraction studies were carried out to investigate the effect of nitric acid concentration in feed solution, U(VI)/Th(IV) ratio and extractant concentration and the results were compared with established solvent such as tri-n-butyl phosphate (TBP) for separation of U(VI) from nitric acid medium. McCabe–Thiele diagrams for extraction as well as stripping of U(VI) were constructed under simulated conditions. Based on batch experiments, six stage counter-current extraction studies were conducted under various TEHP concentration and it was observed that 0.1 M TEHP/n-paraffin was most suitable for selective recovery of U(VI) from a mixture of U(VI)–Th(IV). An optimized condition, 0.1 M TEHP/n-paraffin, 2 M HNO₃ in feed and six number of stages was evaluated for selective extraction and stripping of U(VI) from a solution containing mixture of U(VI)–Th(IV)–Y(III) in nitric acid medium. The U(VI) in strip solution was precipitated using 30 % H₂O₂ at pH ~3. Average particle size of the final precipitate was found to be ~33 μm.