Redox reaction Yb(III) + <Emphasis Type="Italic">e</Emphasis> = Yb(II) in a molten eutectic mixture NaCl-2CsCl

Potentiometric method was used to measure the redox potentials of Yb³⁺/Yb²⁺ in a eutectic melt of sodium and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–973 K. The basic thermodynamic characteristics of the redox reaction YbCl₂(s.) + 1/2Cl₂(g.) ai YbCl₃(s.) were calculated from the conditional standard potentials E*(Yb³⁺/Yb²⁺).     

The electrochemical properties of LiCl-KCl melt held in contact with samarium

The dependence of the reaction capacity (R) of a LiCl (60 mol %)-KCl melt held in contact with samarium at 873 and 973 K on the concentration of the corroding metal in the melt was obtained. The R value was used to estimate the content of Sm²⁺ ions in the lowest oxidation state, their fraction, and the conventional equilibrium constant of the 2Sm³⁺ + Sm ↔ 3Sm²⁺ reaction. The results were used to determine the particular mechanism of currentless transfer of samarium in the chloride melt onto a substrate of a more electropositive metal (in particular, onto nickel).     

Sol-Gel Processing of Sm2+-Doped Glass and Its Spectral Hole Burning at Room Temperature

The sol-gel process was applied to the preparation of Sm²⁺ ion-doped silicate glasses, which show persistent spectral hole burning at room temperature. The gels synthesized by the hydrolysis of metal alkoxides and SmCl₃·6H₂O were heated in air at 500°C, were then reacted with H₂ gas to form the Sm²⁺ ion. The Al₂O₃−SiO₂2 glasses are appropriate to reduce the Sm³⁺ ion with H₂ gas and show intense photoluminescence of Sm²⁺ ion. Persistent spectra hole burning was observed in the excitation spectrum for the⁷F₀→⁵D₀ transition of the Sm²⁺ ion by the irradiation of DCM dye laser. The hole width and depth were ∼16 cm⁻¹ and ∼10% of the total intensity, respectively, at 20°C.     

Enthalpic analysis of the CaTiSiO5 system

The relative enthalpy of titanite and enthalpy of CaTiSiO₅ melt have been measured using drop calorimetry between 823 K and 1843 K. Enthalpies of solution of titanite and CaTiSiO₅ glass have been measured by the use of hydrofluoric acid solution calorimetry at 298 K. Enthalpy of vitrification at 298 K, δ_vitr H(298 K) = (80.7 ± 3.4) kJ mol⁻¹, and enthalpy of fusion at the temperature of fusion 1656 K, δ_fus H(1656 K) = (139 ± 3) kJ mol⁻¹, of titanite have been determined from experimental data. The obtained enthalpy of fusion is considerably higher than up to the present published values of this quantity.     

Thermodynamics of mixed-ligand complexation of cerium group lanthanide ethylenediaminetetraacetates

The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, and Δ _r S) for mixed-ligand complexation of LnEdta⁻ (Ln³⁺ = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺) with iminodiacetate and nitrilotriacetate ions in aqueous solution at 298.15 K and ionic strength I = 0.5 (KNO₃) were determined by calorimetry and pH-metry. The variation of the thermodynamic parameters of the reactions over the lanthanide series was discussed.     

Effect of crystallographic structure on electrical and mechanical characteristics of Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped CeO<Subscript>2</Subscript> films

Electrical conductivity, dielectric permittivity and mechanical hardness of the polycrystalline CeO₂ + xSm₂O₃ (x = 0, 10.9–15.9 mol %) films prepared by Electron Beam Physical Vapour Deposition (EB-PVD) and Ionic Beam Assisted Deposition, (IBAD), techniques were investigated in dependence on their structure and microstructure influenced by the deposition conditions, namely composition, deposition temperature and Ar⁺ ion bombardment. The electrical conductivity of doped ceria prepared without Ar⁺ ion bombardment and investigated by the impedance spectroscopy, IS, was found to be predominantly ionic one under the oxidizing atmosphere/low-temperature conditions and the higher amounts of Sm₂O₃ (>10 mol %) used. The bulk conductivity as a part of total measured conductivity was a subject of interest because the grain boundary conductivity was found to be ∼3 orders of magnitude lower than the corresponding bulk conductivity. Ar⁺ ion bombardment acted as a reducer (Ce⁴⁺ → Ce³⁺) resulting in the development of electronic conductivity. Dielectric permittivity determined from the bulk parallel capacitance measured at room temperature and the frequency of 1 MHz, similarly as the mechanical hardness measured by indentation (classical Vickers and Depth Sensing Indentation-DSI) techniques were also found to be dependent on the deposition conditions. The approximative value of hardness for the investigated films deposited on the substrate was estimated using a simple phenomenological model described by the power function HV = HV ₀ + aP ^b and compared with the so-called apparent hardness (substrate + investigated film) determined by the classical Vickers formula. Results obtained are analyzed and discussed.     

CaWO_4∶xEu~(3+),ySm~(3+),zLi~+红色荧光粉的制备及光学性能

采用微波固相法制备了CaWO_4∶xEu~(3+),ySm~(3+),zLi~+红色荧光粉。测量样品的XRD图、激发谱、发射谱及发光衰减曲线,研究并分析了Eu~(3+)、Sm~(3+)、Li~+的掺杂浓度,对样品微结构、光致发光特性、能量传递及能级寿命的影响。结果表明,Eu~(3+)、Sm~(3+)、Li~+掺杂并未引起合成粉体改变晶相,仍为CaWO_4单一四方晶系结构。Eu~(3+)、Sm~(3+)共掺样品中,Sm~(3+)掺杂为3%时,Sm~(3+)对Eu~(3+)的能量传递最有效。Li~+掺杂起到了助熔剂和敏化剂的作用,使样品发光更强。在394 nm激发下,与CaWO_4∶3%Eu~(3+)样品比较,3%Eu~(3+)、3%Sm~(3+)共掺CaWO_4及3%Eu~(3+)、3%Sm~(3+)、1%Li~+共掺CaWO_4样品的发光分别增强2倍及2.4倍。同一激发波长下,单掺Eu~(3+)样品寿命最短,Sm~(3+)、Eu~(3+)共掺样品随Sm~(3+)浓度增加,寿命先减小后增加,且掺杂了Li~+的样品比不掺Li~+的样品~5D_0能级寿命有所增加。     

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Thermodynamic data for lanthanoid(III) sequestration by phytate at different temperatures

Abstract  

The results of an investigation on the interactions between phytate ion (myo-inositol hexaphosphate, Phy) and some lanthanoid cations (La³⁺, Nd³⁺, Sm³⁺, Dy³⁺, and Yb³⁺) are reported. The stability constants of various LnH _j Phy species (Ln = generic lanthanoid) were determined by potentiometry (ISE-H⁺ glass electrode) in NaCl_aq at I = 0.15 mol dm⁻³ and t = 25 °C, and the corresponding formation enthalpies by calorimetric titration. The thermodynamic data obtained were used to provide a speciation scheme for the lanthanoid(III)–phytate systems at different temperatures. The sequestering ability of this ligand toward Ln³⁺ was also evaluated by calculation of pL₅₀ values (the total concentration of ligand necessary to bind 50% of a cation present in trace amounts) under different conditions, and equations were formulated to model their dependence on temperature and pH.     

Structural and electric properties of the Ce0.8(Sm1 ? xCax)0.2O2 ? δ system (x = 0.0–1.0)

CeO₂-based solid solutions with a fluorite structure are promising materials as electrolytes of medium-temperature electrochemical devices. This work presents the results of systematic studies of structural and electric properties and oxygen nonstoichiometry of the Ce_0.8(Sm_{1 − x} Ca _x )_0.2O_{2 − δ} system in a wide range of concentrations of 0 < x < 1 performed in order to establish the causes affecting the system conductivity and its behavior in a reducing medium. It is found that a single-phase solid solution of the fluorite type is formed in the whole concentration range. Parameters of its lattice cells decrease linearly at an increase in the concentration of Ca²⁺. Conductivity in air grows when calcium is added due to a decrease in the grain boundary resistance. The maximum conductivity in air was obtained for the composition of Ce_0.8(Sm_0.8Ca_0.2)_0.2O_{2 − δ} and is 13.71 × 10⁻³ S/cm at 873 K. Studies of the dependence of conductivity of the partial pressure of oxygen showed that electron conductivity is observed at a higher oxygen partial pressure at an increase in the temperature and calcium concentration. The critical partial pressure of oxygen ( p_O2 ^* )\left( {p_{O_2 }^* } \right) for the compositions of Ce_0.8(Sm_{1 − x} Ca _x )_0.2O_{2 − δ} with x = 0; 0.2, and 0.5 is 1.83 × 10⁻¹⁶, 1.73 × 10⁻¹³, and 3.63 × 10⁻¹³ atm at 1173 K, respectively, and 2.76 × 10⁻²¹, 5.05 × 10⁻¹⁸, and 1.31 × 10⁻¹⁸ atm at 1023 K.     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

Electrochemical study of the reduction of Tm(III) ions in a molten NaCl-2CsCl eutectic

Electrochemical behavior of TmCl₃ solutions in a NaCl-2CsCl eutectic melt at temperatures of 823–973 K on an inert Mo electrode was studied by cyclic and square-wave voltammetry and the method of electromotive forces. The mechanism of the cathodic process was determined, kinetic parameters of the Tm(III) + e ⇆ Tm(II) reaction were found, and the temperature dependence of the diffusion coefficients of Tm(III) ions was calculated. The conditional standard redox potential for the Tm(III)/Tm(II) pair was measured in the temperature range under study. The basic thermodynamic characteristics of the Tm(III) + e ⇆ Tm(II) redox reaction in a molten NaCl-2CsCl eutectic mixture were determined.     

Enthalpy of formation of talc Mg<Subscript>3</Subscript>[Si<Subscript>4</Subscript>O<Subscript>10</Subscript>](OH)<Subscript>2</Subscript> according to dissolution calorimetry

A thermochemical study of natural talc was performed by high-temperature melt dissolution calorimetry on a Tian-Calvet calorimeter. Based on the total values of the increment in enthalpy upon heating the sample from room temperature to 973 K, and of the dissolution enthalpy at 973 K measured in this work for talc and gibbsite (along with those determined for tremolite, brucite, and their corresponding oxides), the enthalpy of formation was calculated for talc composed of elements, Mg₃[Si₄O₁₀](OH)₂, at 298.15 K: Δ_f H _el^o(298.15 K) = −5900.6 ± 4.7 kJ/mol.     

Thermochemical properties of the Fe-analogue of cryolite, Na3FeF6

Relative enthalpies for low-and high-temperature modifications of Na₃FeF₆ and for the Na₃FeF₆ melt have been measured by drop calorimetry in the temperature range 723–1318 K. Enthalpy of modification transition at 920 K, δ_trans H(Na₃FeF₆, 920 K) = (19 ± 3) kJ mol⁻¹ and enthalpy of fusion at the temperature of fusion 1255 K, δ_fusH(Na₃FeF₆, 1255 K) = (89 ± 3) kJ mol⁻¹ have been determined from the experimental data. Following heat capacities were obtained for the crystalline phases and for the melt, respectively: C _p(Na₃FeF₆, cr, α) = (294 ± 14) J (mol K)⁻¹, for 723 = T/K ≤ 920, C _p(Na₃FeF₆, cr, β) = (300 ± 11) J (mol K)⁻¹ for 920 ≤ T/K = 1233 and C _p(Na₃FeF₆, melt) = (275 ± 22) J (mol K)⁻¹ for 1258 ≤ T/K ≤ 1318. The obtained enthalpies indicate that melting of Na3FeF6 proceeds through a continuous series of temperature dependent equilibrium states, likely associated with the production of a solid solution.      

Uptake of some lanthanides on γ-zirconium phosphate-phosphite and its 1,10-phenanthroline and 2,2-bipyridyl intercalated products

γ-Zirconium phosphate-phosphite, γ-Zr·PO₄·H₂PO₃·2H₂O, (γ-ZrPP), was prepared and characterized. Direct treatment of γ-zirconium phosphate-phosphite with an ethanol solution of 0.1M 1,10-phenanthrolin and 2,2'-bipyridyl gave the well defined composites, γ-Zr·PO₄·H₂PO₃(phen)_0.15·H₂O and γ-Zr·PO₄·H₂PO₃(bipy)_0.18·0.6H₂O respectively.K _d values of a mixture of lanthanide ions: La³⁺, Sm³⁺, Eu³⁺ and Yb³⁺ for the intercalated products and for γ-ZrPP in HNO₃ solution at room temperature and at pH 2 and 4 were determined by a radiotracer technique.¹⁴⁰La,^152mEu,¹⁵³Sm and¹⁷⁵Yb radioisotopes were used for the equilibration experiment using 500 μl (4.0·10⁻⁵ mmole) each of the solutions of the tracers as a mixture in 7.5 M HNO₃ solution at the desired pH with 0.1 g of γ-ZrPP and of the intercalated products. The selectivity order was found to be dependent on the nature of the ligand and on the pH. The 2,2'-bipyridyl product posseses, at pH 2 in general, a highK _d value, specially for Sm³⁺ (9815.9) compared to that of the 1,10-phenanthrolin product (3375.5) and to γ-ZrPP (419.8). This could be attributed to partial deintercalation of the 2,2'-bipyridyl at pH 2 and increasing of ionogenic groups.     

Electrochemical and thermodynamic properties of thulium trichloride in a molten NaCl-KCl-CsCl eutectic

Potentiometric method was used to measure the redox potentials of Tm³⁺/Tm²⁺ in a eutectic melt of sodium, potassium, and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–973 K. The main thermodynamic characteristics of the redox reaction TmCl_2(solution) + 1/2Cl_2(g) ⇆ TmCl_3(solution) were calculate from the conditional standard potentials $ E_{{{Tm^{3 + } } \mathord{\left/ {\vphantom {{Tm^{3 + } } {Tm^{2 + } }}} \right. \kern-\nulldelimiterspace} {Tm^{2 + } }}}^* $ E_{{{Tm^{3 + } } \mathord{\left/ {\vphantom {{Tm^{3 + } } {Tm^{2 + } }}} \right. \kern-\nulldelimiterspace} {Tm^{2 + } }}}^* .     

Synthesis and structures of nine-coordinate K[SmIII (Edta)(H2O)3] · 2H2O and Ten-Coordinate K2[SmIII(Pdta)(H2O)2]2 · 4.5H2O complexes

The title complexes, K[Sm^III(Edta)(H₂O)₃] · 2H₂O(I)(H₄Edta = ethylenediamine-N,N,N′,N′-tetraacetic acid) and K₂[Sm^III(Pdta)(H₂O)₂]₂ · 4.5H₂O (II) (H₄Pdta = propylenediamine-N,N,N′,N′-tetraacetic acid), were prepared and their compositions and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques, respectively. Complex I has a mononuclear structure, and the Sm³⁺ ion is nine-coordinated by an Edta ligand and three water molecules, yielding a pseudo-monocapped square antiprismatic conformation, and the complex crystallizes in the orthorhombic crystal system with space group Fdd2. The crystal data are as follows: a = 19.84(5), b = 35.58(9), c = 12.15(3) ?, V = 8580(38) ?³, Z = 16, ρ _c = 1.925 g/cm³, μ = 3.010 mm⁻¹, F(000) = 4976, R = 0.0252, and wR = 0.0560 for 3510 observed reflections with I ≥ 2σ(I). Complex II has a binuclear structure and the Sm³⁺ ion is ten-coordinated by a Pdta ligand, two oxygen atoms from a carboxylic group of adjacent Pdta ligand and two water molecules, yielding a distorted bicapped square antiprismatic prism. The complex crystallizes in the triclinic crystal system with space group P $ \bar 1 $ \bar 1 . The crystal data are as follows: a = 8.9523(15), b = 10.7106(15), c = 11.6900(19) ?, α = 80.613(5)°, β = 80.397(5)°, γ = 76.530(4)°, V = 1065.7(3) ?³, Z = 1, ρc = 1.970 g/cm³, μ = 2.532 mm⁻¹, F(000) = 1620, R = 0.0332 and wR = 0.0924 for 5390 observed reflections with I ≥ 2σ(I).     

Cloning,Expression, and Characterization of a Wide-pH-Range Stable Phosphite Dehydrogenase from <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. K in <Emphasis Type="Italic">Escherichia coli</Emphasis>

A phosphite dehydrogenase gene (ptdhK) consisting of 1,011-bp nucleotides which encoding a peptide of 336 amino acid residues was cloned from Pseudomonas sp. K. gene ptdhK was expressed in Escherichia coli BL21 (DE3) and the corresponding recombinant enzyme was purified by metal affinity chromatography. The recombinant protein is a homodimer with a monomeric molecular mass of 37.2 kDa. The specific activity of PTDH-K was 3.49 U mg⁻¹ at 25 °C. The recombinant PTDH-K exhibited maximum activity at pH 3.0 and at 40 °C and displayed high stability within a wide range of pHs (5.0 to 10.5). PTDH-K had a high affinity to its natural substrates, with K _m values for sodium phosphite and NAD of 0.475 ± 0.073 and 0.022 ± 0.007 mM, respectively. The activity of PTDH-K was enhanced by Na⁺, NH₄⁺, Mg²⁺, Fe²⁺, Fe³⁺, Co²⁺, and EDTA, and PTDH-K exhibited different tolerance to various organic solvents.     

Electroreduction of cerium(III) ions on a silver electrode in a chloride melt at 823 K

The electroreduction of cerium ions in a KCl-NaCl-CsCl eutectic melt at 823 K was studied. The electroisolation of metallic cerium from halide complexes was conducted at potentials higher than the potentials of the decomposition of alkali halide melts and shown to be the primary electrochemical process. The mechanism of the electrode process was determined.     

Tysonite-type solid solutions in the BiF<Subscript>3</Subscript>-BiOF-BaF<Subscript>2</Subscript> system: Polymorphism and anionic conductivity

Tysonite solid solutions Bi_1−x Ba _x O _y F_3−x−2y in the BiF₃-BiOF-BaF₂ system were obtained by solid-phase synthesis in sealed copper tubes in an argon atmosphere at 873 K with subsequent quenching. The solid solutions were studied by X-ray diffraction, electron diffraction, and impedance spectroscopy. On the basis of X-ray powder diffraction data, the homogeneity ranges of the tysonite solid solutions were determined and the scheme of their location in the BiF₃-BiOF-BaF₂ system at 873 K was suggested. Aliovalent substitutions in both the cation and anion sublattices Ba²⁺ → Bi³⁺ and O²⁻ → F⁻ made it possible to vary the concentration of anion vacancies. It was found that, at a high concentration of anion defects at 873 K, the hexagonal tysonite modification with space group P6₃/mmc is stable. With a decrease in the defect concentration, the trigonal tysonite modification with space group $ P\bar 3c1 $ P\bar 3c1 becomes stable. An ordered monoclinic tysonite-type modification BiO _y F_{3 − 2y} (0.13 < y < 0.23) was revealed. For the homogeneity ranges of all tysonite phases, dependences of the unit cell parameters and conductivity on the composition along the sections with a constant barium or oxygen content were reported. The most probable location of oxygen anions and anion vacancies in the tysonite structure is discussed.