Influence of conditions on the potential of the couple of nonoxygenated U5+/U4+ ions bound in complexes with the P2W17O 6110? and SiW11O 398? anions

The formal potential of the couple of nonoxygenated U⁵⁺/U⁴⁺ ions bound in complexes with unsaturated heteropoly anions (HPAs) P₂W₁₇O₆₁¹⁰⁻ (I) and SiW_{11 O39}⁸⁻ (II) in 0–1 M NaNO₃ and 1 M (NaCl + HCl) in the range of pH 0.7–4.7 was measured. In 1 M NaNO₃ solutions at pH 4.7–3.0 for I and 4.3–3.9 for II, the formal potentials are constant: 0.820 and 0.730 V, respectively. They preserve approximately the same value with a decrease in pH to 0.7 in 1 M (NaCl + HCl). The potential noticeably decreases with a decrease in the NaNO₃ or NaCl concentration from 1 M to 0 (pH 4.1–4.7): to 0.09 and 0.05–0.06 V for I and II, respectively. Approximate constancy of the potential of the U⁵⁺/U⁴⁺ couple with a decrease in pH to 1 and lower distinguishes this couple from the M⁴⁺/M³⁺ couples (M = Ce, Am, Bk) whose potential appreciably grows with increasing acidity. This is due to the fact that the U⁵⁺ and M⁴⁺ ions in acid solutions remain in the form of complexes with the ratio M: HPA = 1: 2, whereas the M³⁺ ions pass into the form of 1: 1 complexes. Thus, variation of the formal potentials of all the M ^{n + 1}/M ⁿ⁺ couples in the presence of H⁺ and Na⁺ ions is associated with variation of the stability constants of the complexes M(HPA)₂, which, in turn, is caused by interaction of single-charged ions with HPA. However, the H⁺ and Na⁺ ions interact with HPA by different mechanisms and therefore affect the potential of the U⁵⁺/U⁴⁺ couple differently. Original Russian Text ? V.P. Shilov, A.B. Yusov, A.M. Fedoseev, Ph. Moisy, 2008, published in Radiokhimiya, 2008, Vol. 50, No. 5, pp. 393–396.     

State of difficultly soluble uranosilicates MIHSiUO6 ? nH2O (M + = Li+, Na+, K+, Rb+, Cs+, NH4+) in saturated aqueous solutions

The solubility of uranosilicates M^IHSiUO₆ nH₂O (M^I = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH ₄ ⁺ ) in aqueous solutions at 25°C was studied experimentally. The equilibrium constants of reactions that occur at dissolution of uranosilicates in acidic and neutral solutions were calculated. The composition of the equilibrium solutions was studied. The standard Gibbs energies of formation of the compounds were calculated from the solubility data. The behavior of the uranosilicates under various conditions was predicted on the basis of the previously suggested quantitative physicochemical model of the state of the heterogeneous system crystalline uranosilicate-aqueous solution.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 418–422.Original Russian Text Copyright © 2004 by Chernorukov, Nipruk, Knyazev, Pegeeva.     

Molten salt synthesis of Cr3C2-coated flake graphite and its effect on the physical properties of low-carbon MgO–C refractories

To improve the performance of low-carbon MgO–C refractories, the Cr₃C₂-coated flake graphite was synthesized by molten salt method, then the Cr₃C₂-coated flake graphite was added to low-carbon MgO–C refractories. In this work, the effects of reaction temperature, Cr/C mole ratio, and holding time on the synthesis of Cr₃C₂-coated flake graphite were studied. Furthermore, the effect of Cr₃C₂-coated flake graphite on the physical properties of low-carbon MgO–C refractories was evaluated. The results indicated that when the reaction temperature was 950 °C, Cr/C molar ratio was 1/2 and holding time was 3 h, the synthesized Cr₃C₂-coated flake graphite had fewer surface micropores and the crystallinity of Cr₃C₂ grains was high. In addition, the Cr₃C₂-coated flake graphite exhibited excellent oxidation resistance. MgO–C refractories containing 2 wt% Cr₃C₂-coated flake graphite exhibited more excellent physical properties. The results of nano CT detection system showed that the addition of Cr₃C₂-coated flake graphite promoted the densification of MgO–C refractories.     

Low-temperature synthesis of δ-MnO2 with large surface area and its capacitance

δ-MnO₂ was synthesized by a facile low-temperature hydrothermal method with a mixed system of KMnO₄ and CO(NH₂)₂ at 90 °C for 24 h. The obtained product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N₂ adsorption-desorption. Results showed that the as-synthesized product had a layered structure and a high specific surface area of 230 m² g^− 1. Electrochemical characterization indicated that the prepared material exhibited an ideal capacitive behavior with the initial capacitance value of 265 F g^− 1 in 1 mol L^− 1 Na₂SO₄ aqueous solution at a scan rate of 5 mV s^− 1 and excellent cycling behavior.     

Combustion synthesis of Eu2?+? and Dy3?+? activated Sr3(VO4)2 phosphor for LEDs

Combustion synthesis and photoluminescence (PL) characterization of Sr₃(VO₄)₂:Eu,Dy phosphors are presented in this paper. PL emission of Sr₃(VO₄)₂:Eu phosphor shows green broad emission band centring at 511 nm and a red sharp band at 614 nm by excitation wavelength of 342 nm. The PL emission spectrum of Sr₃(VO₄)₂:Dy phosphor exhibits an intense blue emission peak at 479 nm, yellow broad band centring at 573 nm and red band at 644 nm by the excitation wavelength of 426 nm in near visible blue region. The excitation wavelength of Eu (342 nm) and Dy (426 nm) activated Sr₃(VO₄)₂ phosphor are well matched with the excitation of near UV excited solid state lighting and blue chip excitation of light emitting diodes, respectively. The effect of Eu^2 +and Eu^3 +ions concentration on the emission intensity of Sr₃(VO₄)₂ was also investigated. The Sr₃(VO₄)₂:Eu is a potential green and red emitting phosphor as well as Sr₃(VO₄)₂:Dy is blue and yellow emitting phosphor for solid state lighting i.e. white LEDs. The XRD and SEM characteristics of Sr₃(VO₄)₂ materials was also reported in this paper.     

Magnetic susceptibility and effective magnetic moment of the Nd3+ and Co3+ ions in NdCo1 ? x Ga x O3

The magnetic susceptibility of NdCo_{1 − x} Ga _x O₃ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.8, 0.9, 1) has been measured at temperatures from 80 to 950 K. The effective magnetic moments (μ_eff) due to the magnetic moments of the Co³⁺ and Nd³⁺ ions have been determined in the temperature ranges of Curie-Weiss behavior, 130–370 and 600–940 K, and have then been used, together with the effective magnetic moment of Nd³⁺ (3.62μ_B or 4.20μ_B), to evaluate the effective magnetic moment of Co³⁺ in NdCo_{1 − x} Ga _x O₃. For the solid solutions with < 2.83μ_B, we have determined the fractions of intermediate-and low-spin Co³⁺ ions. In the range 2.83μ_B < < 4.90μ_B, we have determined the fraction of high-spin Co³⁺ ions. The results indicate that, in the temperature range 130–370 K, the Co³⁺ ions in NdCo_{1 − x} Ga _x O₃ with x = 0, 0.5, 0.8, and 0.9 are in the intermediate-and high-spin states, and the fraction of high-spin Co³⁺ ions gradually increases from 10% at x = 0 to 67% at x = 0.9. In the solid solutions with x = 0.1, 0.2, 0.3, and 0.7, more than half of the Co³⁺ ions are in the low-spin state, and the rest are in the intermediate-spin state. In the temperature range 600–940 K, the Nd³⁺ ions are in the ground and excited states, with theoretically predicted of of 3.62μ_B and 5.52μ_B, respectively. Because of the significant uncertainty in in this temperature range, has been determined less accurately compared to the range 130–370 K. Original Russian Text ? N.N. Lubinskii, L.A. Bashkirov, A.I. Galyas, S.V. Shevchenko, G.S. Petrov, I.M. Sirota, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 9, pp. 1137–1143.     

The Pseudogap and the Superconducting Order Parameter in Inhomogeneous Bi2Sr2CaCu2O8+δ

Recent experiments on Bi₂Sr₂CaCu₂O₈₊ (Bi2212) have provided compelling evidence that the samples are inhomogeneous on a nanoscale, with spatially separated superconducting gap (SG) and nonsuperconducting, pseudogap (PG) regions that arise from hole–hole and particle–hole pairings, respectively. We compare and contrast the nonphase sensitive experiments that cannot distinguish these orderings from the phase-sensitive experiments that can. Although the wave vector dependence of the pseudogap is highly anisotropic, we conclude that in Bi2212, the c-axis quasiparticle tunneling is incoherent and that the c-axis supercurrent arises solely from a rather isotropic s-wave superconducting order parameter (OP) for T < T_c.     

The upconversion luminescence properties of the Yb3+–Ho3+ system in nanocrystalline Y2O2S

Near-spherical Y₂O₂S:Yb³⁺,Ho³⁺ nanocrystals (NCs) with an average particle size of 40 nm were synthesized by the coprecipitation method followed by a solid–gas sulfuration technique. The effects of the Ho³⁺ ion doping concentration on the upconversion luminescence (UCL) property of the NCs was studied through the UCL spectra. Results show that the UCL intensity of Y₂O₂S:Yb³⁺,Ho³⁺ NCs markedly changes with Ho³⁺ ion concentration, and that the Ho³⁺ ion concentration quench is observed at 0.25 mol%. This value is only half as much as that in micron Y₂O₂S prepared by a solid state reaction, which can be attributed to the distinct diffusion mechanism of activator ions in the coprecipitation process. In addition, strong red emissions can be observed in Y₂O₂S:Yb³⁺,Ho³⁺ NCs throughout all Ho³⁺ doping concentrations used. However, the Ho³⁺ in micron Y₂O₂S usually exhibits weak red UCL. Infrared spectra confirm that this result is related to the large vibrational quanta produced by OH⁻ and CO₃ ²⁻ groups adsorbed onto the surface of NCs. These large vibrational quanta can remarkably increase the probability of ⁵S₂–⁵F₅ and ⁵I₆–⁵I₇ multiphonon relaxation, leading to the enhancement of red emissions arising from ⁵F₅ → ⁵I₈ transitions. The UCL mechanism of the Yb³⁺–Ho³⁺ system in nano- and microsized Y₂O₂S is also discussed.     

Evidence for High T C Superconducting Transitions in Isolated Al 45? and Al 47? Nanoclusters

Heat capacities measured for Al₄₅⁻ and Al₄₇⁻ nanoclusters have reproducible jumps at ∼200 K. These jumps are consistent with theoretical predictions that some clusters with highly degenerate electronic states near the Fermi level will undergo a transition into a high T _C superconducting state. An analysis based on a theoretical treatment of pairing in Al₄₅⁻ and Al₄₇⁻ agrees well with the experimental data in both the value of the critical temperature and in the size and width of the jumps in the heat capacity.     

Bi3+/Eu3+共掺Y2MgTiO6荧光粉的发光性能研究

采用高温固相法合成了Bi³⁺和Eu³⁺共掺的Y₂MgTiO₆荧光粉,X射线衍射谱(XRD)分析表明,所有样品的晶体结构均为单斜晶系P2₁/n, Bi³⁺和Eu³⁺掺入Y₂MgTiO₆中并替代Y³⁺的位置。通过光致发光光谱、X射线激发荧光谱(XEL)系统研究了Bi³⁺和Eu³⁺掺杂浓度与发光强度之间的关系。荧光分析表明,Y₂MgTiO₆∶Bi³⁺,Eu³⁺荧光粉可被271nm左右的近紫外光激发,在620nm处表现出较强的红光发射带,这一发光属于Eu³⁺的⁵D₀→⁷F₂特征跃迁;当Eu³⁺掺杂量为20%(摩尔分数)...     

Systematics of the thermopower below Tc in Tl2Ba2CaCu2O8+δ

A systematic study of the mixed-state thermopower in Tl₂Ba₂CaCu₂O₈₊ indicates a that there are two contributions to the total signal. The largest contribution is accurately proportional to the resistivity, as previously reported. We have also identified a new, additional contribution to the thermopower. The source of the excess thermopower is not presently determined, and may be related to vortex fluctuations or d-wave superconductivity.This work is supported in part by USAFOSR F49620-93-1-0310, NSF Grant No. DMR 91-22043, ARPA Grant MDA 972-90-J-1001, the Texas Center for Superconductivity at the University of Houston, and the T.L.L. Temple Foundation.     

白光LED用Sr3-x-yMySiO5:Eux2+系列发光材料性能的研究

采用高温固相法合成白光LED用Sr3-x-yMySiO5:Eu2x+(M=mg2+、Ca2+、Ba2+、Zn2+等)发光材料,优化荧光粉的合成条件,测定样品的光谱数据,寻找Eu2+和Mg2+、Ca2+、Ba2+、Zn2+等的最佳掺杂量,使其在460nm蓝光激发下得到最优的光谱性能。     

Microwave-assisted synthesis and humidity sensing of nanostructured α-Fe2O3

Nanocrystalline α-Fe₂O₃ has been prepared on a large-scale by a facile microwave-assisted hydrothermal route from a solution of Fe(NO₃)₃·9H₂O and pentaerythritol. A systematic study of the morphology, crystallinity and oxidation state of Fe using different characterization techniques, such as transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy was performed. It reveals that nanostructured α-Fe₂O₃ comprises bundles of nanorods with a rhombohedral crystalline structure. The individual nanorod has 8-10 nm diameter and ∼50 nm length. The as-prepared nanostructured α-Fe₂O₃ (sensor) gives selective response towards humidity. The sensor shows high sensitivity, fast linear response to change in the humidity with almost 100% reproducibility. The sensor works at room temperature and rejuvenates without heat treatment. The as-prepared nanostructured α-Fe₂O₃ appears to be a promising humidity sensing material with the potential for commercialization.     

Effect of SiO 32? /OH? on plasma electrolytic oxidation of Ti-5Mo-4V-3Al

Plasma electrolyte oxidation (PEO) was utilized to produce thick films on titanium and Ti-5Mo-4V-3Al alloys by immersing them in various solutions of Na₂SiO₃ and KOH with different concentrations to investigate the effect of SiO₃²⁻/OH⁻ relations on the morphology and formed phases by utilizing SEM and XRD. Corrosion resistance is evaluated by open circuit potential (OCP) variation of samples in NaCl 3.5% and potentiodynamic polarization. The results show that the unstable film is formed by using more aggressive PEO electrolyte. By increasing this ratio, pore size varied from fine to coarse and the rate of corrosion decreased and OCP became more positive. The best protective film was formed in SiO₃²⁻/OH⁻ ratio of 1.     

Enhancement of the Current Density J C for Bi2Sr2CaCu2O8 by?Means of Carbon and NbSe2 Nanotubes

Three polycrystalline Bi₂Sr₂CaCu₂O₈, Bi₂Sr₂CaCu₂O₈ with carbon nanotubes, Bi₂Sr₂CaCu₂O₈ with NbSe₂ nanotubes were synthesized by solid state reaction method and studied by scanning electron microscopy, X-ray diffraction, magnetization measurements, and high resolution transmission electron microscopy. The critical temperature T _C for the three compounds was about 85 K. There is an enhancement in the critical current density, J _C for samples with carbon and NbSe₂ nanotubes as compared with pure Bi₂Sr₂CaCu₂O₈. The enhancement provides evidence that wetting exists for the two doped samples investigated.      

Facile synthesis and characterization of ZnFe2O4/α-Fe2O3 composite hollow nanospheres

ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres were successfully fabricated via a facile one-pot solvothermal method, utilizing polyethylene glycol as soft template. X-ray diffraction and scanning electron microscopy analysis revealed that the prepared nanospheres with cubic spinel and rhombohedra composite structure had a uniform diameter of about 370 nm, and the hollow structure could be further confirmed by transmission electron microscopy. Energy dispersive X-ray, X-ray photoelectron spectroscopy and Fourier transform infrared techniques were also applied to characterize the elemental composition and chemical bonds in the hollow nanospheres. The ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres show attractive light absorption property for potential applications in electronics, optics, and catalysis.     

Hydrothermal synthesis and catalytic properties of α- and β-MnO2 nanorods

One-dimensional α-MnO₂ and β-MnO₂ single-crystalline nanostructures were prepared by hydrothermal process. The products were characterized in detail by multiform techniques: X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Experimental results indicate that the temperature plays important roles in determining produce α-MnO₂ and β-MnO₂ nanorods. In addition, the as-prepared α-MnO₂ and β-MnO₂ nanorods showed excellent catalytic performance in the Fenton-like reaction.     

Redox equilibrium U(VI) + 2Ce(III) ? U(IV) + 2Ce(IV) in the presence of unsaturated heteropoly anions P2W17O 6110? and SiW11O 398?

The equilibrium of the reaction U(VI) + 2Ce(III) ⇄ U(IV) + 2Ce(IV) in the presence of unsalurated heleropoly compounds K₁₀P₂W₁₇O₆₁ and K₈SiW₁₁O₃₉ in 0.01–1.0 M HClO₄ solutions (ionic strength 1) was studied. The potential of the Ce(IV)/Ce(III) couple in K₈SiW₁₁O₃₉ solutions was measured, from which the overall stability constants β₂^IV of the complexes U^IV(SiW₁₁O₃₉)₂¹²⁻, equal to 10^23.8 and 10^19.8 in 0.1 M HClO₄ + 0.9 M NaClO₄ and in 1.0 M HClO₄, respectively, were calculated. Under the same conditions, for the complex U^IV(P₂W₁₇O₆₁)₂¹⁶⁻ β₂^IV = 10^23.2 and 10^18.5 (the latter value was obtained by extrapolation or data for 0.1 M HClO₄ + 0.9 M NaClO₄ solution). Original Russian Text ? V.P. Shilov. A.B. Yusov, M.N. Sokohva. A.M. Fedoseev, 2008, published in Radiokhimiya, 2008, Vol. 50. No. 3, pp. 203–208.     

Solution combustion synthesis of γ(L)-Bi2MoO6 and photocatalytic activity under solar radiation

The facile method of solution combustion was used to synthesize γ(L)-Bi₂MoO₆. The material was crystallized in a purely crystalline orthorhombic phase with sizes varying from 300 to 500 nm. Because the band gap was 2.51 eV, the degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (<1 m²/g) of the synthesized material, γ(L)-Bi₂MoO₆ showed high photocatalytic activity under solar radiation due to its electronic and morphological properties.