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.     

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.     

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.     

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.     

Optical conductivity of a superconductor withdx2?y2 symmetry

Using a simplified Eliashberg formulation in which we keep only that part of the susceptibility which is separable and of symmetry in the pairing channel and keep the isotropic part in the renormalization channel, we have calculated the ac conductivity in the superconducting state. At zero temperature, in the clean limit, we find a finite amount of absorption at any frequency, however small, although it is substantially reduced over its normal-state value. Besides this boson-assisted absorption, when impurities are added a new channel is opened up in which momentum is given up to the impurity system and absorption proceeds directly through the creation of a hole-particle pair. Born and unitary impurity scattering are considered.This research was supported in part by the Canadian Institute for Advanced Research (CIASR), by the Ontario Centre for Materials Research (OCMR), and by the Natural Sciences and Engineering Research Council o f Canada (NSERC).     

Heterogeneous equilibria in aqueous solutions of uranophosphates MII(PUO6)2·nH2O (MII = Mg2+, Ca2+, Sr2+, Ba2+)

The stability of uranophosphates M^II(PUO₆)₂·nH₂O (M^II = Mg, Ca, Sr, Ba) in aqueous solutions at pH from 0 to 14 was studied. These compounds preserve their composition and structure in the interval of pH 1–11 and congruently pass into the solution within the limits of their solubility. In strongly acidic media (pH < 1), alkaline-earth metal uranophosphates transform into uranophosphoric acid HPUO₆·4H₂O. In alkaline solutions at pH > 11, the uranophosphates MII(PUO₆)₂·nH₂O irreversibly transform into diuranates. Using the methods of equilibrium thermodynamics, the solubility products and Gibbs functions of formation of alkalineearth metal uranophosphates were calculated, the solubility curves were calculated and experimentally confirmed, and the speciation diagrams of U(VI) and P(V) in solutions and in equilibrium solid phases were constructed.     

Redox equilibrium U(IV) + 2Fe(CN) 63? ? U(VI) + 2Fe(CN) 64? in solutions of unsaturated heteropoly anions: Potentials of redox couples, stability of U(IV) complexes, reaction mechanism

The kinetics and equilibria of the reactions UO₂²⁺ + 2L + 2Fe(CN)₆⁴⁻ ⇄ UL₀ + 2Fe(CN)₆³⁻ in 0.1–1.0 M HCl solutions (ionic strength 1.0), where L is heteropoly anion of the composition P₂W₁₇O₆₁¹⁰⁻ or SiW₁₁O₃₉⁸⁻, were studied speelrophotometrically. Measurement of the redox potential of the ferri/rerrocyanide couple in acid solutions allowed estimation of the stability constants of the complxes U^IV(P₂W₁₇O₆₁)₂¹⁶⁻ and U^IV(SiW₁₁O₃₉)₂¹²⁻, equal in 1 M H⁺ solutions to 10^18.6 and 10^21.O, respectively. Accumulation of U^IVL₂ formed by reduction of UO₂²⁺ follows a first-order rate law, i.e., it involves the formation of UO₂⁺ which slowly reacts with L. The arising complex rapidly reacts with UO₂⁺. The loss of UL₂ occurs via formation of the complex of nonoxygenated U(V) with the heleropoly anion. Original Russian Text ? V.P. Shihv, A.B. Yusov. M.N. Sokolova, A.M. Fedoseev, 2008, published in Radiokhimiya, 2008, Vol. 50, No. 3, pp. 209–214.     

胶原纤维固化单宁对U6+的吸附特性研究

采用胶原纤维固化单宁(CFIT)作为吸附材料,系统研究了该吸附剂在模拟放射性废水中对U6+的吸附特性,离子溶液的pH值、吸附剂量、温度、时间和初始浓度等因素对U6+去除率的影响都进行了初步探讨,对吸附过程中的反应动力学、热力学参数以及等温吸附规律进行了分析。胶原纤维固化单宁对U6+有良好的吸附效果,当pH值在5.5左右,吸附时间为4h时,铀的去除率可达96.58%。通过吸附热的计算得出胶原纤维固化单宁在高温下的吸附可自发进行(ΔH=19.2942kJ/mol)。等温吸附研究表明,静态吸附动力学可以用准二级速度方程来描述,胶原纤维固化单宁对U6+的吸附行为符合Langmuir等温吸附方程,说明胶原纤维固化单宁对U6+的吸附是以单分子层吸附(化学吸附)为主,通过拟合得出最大吸附量为352.1127mg/g。     

The synthesis of the first stage graphite salt C8+AsF6− and its relationship to the first stage graphite/AsF5 intercalate

Oxidation of graphite with excess O₂⁺AsF₆^?, in suspension in SO₂C1F, produces the blue first-stage graphite salt of composition C₈AsF₆, which X-ray single crystal photographs show is hexagonal with a = 4.92(2), c = 8.10(2), $\text{V}\text{= 170}\text{A}\text{?}{}^3$. The blue first-stage material of approximate composition C₁₀AsF₅ obtained from graphite and AsF₅ has a related pseudo cell. Arsenic X-ray absorption-edge spectra show that C₈AsF₆ contains AsF₆^? alone, and that the graphite/AsF₅ intercalte contains AsF₆^? and AsF₃ in accord with the AsF₅ reduction:

$\text{3 AsF}{}_5\text{+ 2 e}{}^{\mathrm{?}}\text{→ 2 AsF}{}_6{}^{\mathrm{?}}\text{+ AsF}{}_3$

Treatment of the graphite/AsF₅ compound with F₂ gas results in conversion of all of the intercalated arsenic to AsF₆^?.     

Crystal structure of a double Np(V) and Co(NH3)63+ maleate, Co(NH3)6[NpO2(HL)2(H2O)3](HL)2?H2O [L = OOC(HC)2COO]

Crystal structure of a double Np(V) and Co(NH₃) ₆ ³⁺ maleate Co(NH₃)₆[NpO₂(HL)₂(H₂O)₃](HL)₂H₂O [L = OOC(HC)₂COO] was studied. The crystal structure consists of complex anions [NpO₂(HL)₂(H₂O)₃]^–, HL^– anions, [Co(NH₃)₆]³⁺ cations, and water molecules of crystallization. Hydrogen bonds in which proton donors are water molecules and hexaamminecobalt cations link structural fragments to form a 3D network. The coordination polyhedra of the Np(V) atoms are pentagonal bipyramids whose equatorial planes are formed by oxygen atoms of two HL^– anions and three water molecules. Four crystallographically independent maleate anions were identified in the structure. Two of these anions enter into the Np(V) surrounding, and their coordination capacity is 1.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 521–523.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

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.     

CaF2:Yb3+/Er3+/X(X= Li+, Na+, K+)近红外二区发光性能研究

利用热分解法制备了CaF₂:Yb³⁺/Er³⁺纳米颗粒,通过改变Yb³⁺和Er³⁺的掺杂浓度对其近红外二区(NIR-II)发光性能进行调节,研究结果表明,当Yb³⁺掺杂浓度为20%,Er³⁺掺杂浓度为2%时,在980 nm光源激发下,NIR-II发光性能最强,且纳米颗粒分散性良好,尺寸均匀。然后,进一步研究了不同的碱金属离子(Li⁺、Na⁺、K⁺)共掺杂对其NIR-II发光性能的影响,研究结果表明,Li⁺掺杂因不利于纳米颗粒成核导致NIR-II发光性能降低,Na⁺和K⁺掺杂均有利于NIR-II发光性能提升。相比而言,K⁺离子半径更大,更有利于破坏晶体场的局部对称性,因此,在K⁺共掺杂的情况下NIR-II发光性能最强。     

Ln(Ln=Gd3+,Cu+,Sm3+,Dy3+)助激活的Ca8Mg（SiO4）4Cl2∶Eu2+荧光粉的光谱特性和Eu2+的格位计算

采用高温固相法合成了掺杂Ln(Ln=Gd3+,Cu+,Sm3+,Dy3+)作助激活离子的氯硅酸镁钙荧光粉。通过X射线衍射(XRD)对Ca8Mg(SiO4)4Cl2∶Eu2+,Ln进行了表征,结果表明Ln的共掺杂并没有影响基质晶体的面心立方结构。所合成的荧光粉发射峰值位于507nm的绿光区,激发光谱在330~430nm之间均有较强吸收,与紫光InGaN芯片(395nm)相匹配。掺杂Ln作助激活剂增强了荧光粉的发光强度。借助Uitert经验公式计算出Eu2+在Ca8Mg(SiO4)4Cl2基质中占据八配位Ca(Ⅱ)格位。     

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.     

Er3+/Yb3+掺杂NaGd(WO4)2粉体的制备与发光性能

采用水热法成功制备了Er~(3+)/Yb~(3+)双掺杂的NaGd(WO_4)_2纳米粉体,研究了不同络合剂、水热温度对样品形貌和结构的影响。测量了不同Er~(3+)掺杂浓度样品的可见上转换和近红外发射光谱。结果表明:在980nm LD激发下,可观测到样品强烈的绿色上转换发光,对应Er~(3+)的~2H_(11/2)→~4I_(15/2)(530nm)和~4S_(3/2)→~4I_(15/2)(552nm)跃迁,以及较弱的红色上转换和近红外发光,分别对应Er~(3+)的~4F_(9/2)→4I15/2(656nm)和~4I_(13/2)→~4I_(15/2)(1 532nm)跃迁。且随着Er~(3+)掺杂浓度的增加,样品的上转换红绿光和1.54μm附近的近红外光均呈现出先增大后减小的趋势。样品的激发和发射光谱显示,在378nm处的激发峰最强,对应Er~(3+)的~4I_(15/2)→~4 G_(11/2)能级跃迁,最强发射峰位于552nm。根据泵浦功率与发光强度的关系可以得出,红光和绿光的发射主要为双光子吸收过程,但红光还包含了一定的单光子吸收成分。     

Zn2+含量对Ca0.925-xZnxMoO4:Eu0.0753+红色荧光粉发光性能的影响

采用溶胶-凝胶法制备了Ca0.925-xZnxMoO4∶Eu30+.075红色荧光粉,并对粉体的物相结构、发光性能、粒径方面进行研究。实验得出,适量的Zn2+取代Ca2+没有改变Ca0.925MoO4∶Eu30+.075的晶体结构,而且明显提高了Ca0.925-MoO4∶Eu30+.075的发光强度。同时,掺杂Zn2+可以使红色荧光粉Ca0.925-xZnxMoO4∶Eu30+.075的电荷吸收带发生红移,Zn2+的最佳掺杂量为7%(原子分数)。对Ca0.925MoO4∶Eu30+.075和Ca0.855Zn0.07MoO4∶Eu30+.075进行对比研究,得出Ca0.855Zn0.07MoO4∶Eu30+.075的粒径稍大,但是其发光性能优于Ca0.925MoO4∶Eu30+.075。     

Reducing ultra-low thermal expansion of β-Zr2O(PO4)2 by substitutions?

The ultra-low thermal expansion of β-Zr₂O(PO₄)₂ could still be reduced by chemical modifications, according to previous works on uranium and thorium IV homologues that evidenced a contracting effect of big cations. However, the present study shows that the only isovalent cations likely to substitute for Zr^IV or P^V are either harmful, or unstable, chemically or thermally. Furthermore, aliovalent modifications seem to be forbidden by the crystal structure of the material, leaving probably very few perspectives of improvement. Vanadium however improves significantly the crystallinity of the material and lowers the α-β transition temperature.     

NH4+扩层MoS2的制备及其储锌性能研究

二硫化钼(Mo S₂)作为水系锌离子电池的正极材料,受到锌离子(Zn²⁺)与主体框架之间的强静电相互作用表现出缓慢的反应动力学。并且Mo S₂的层间距较窄难以嵌入大尺寸水合Zn²⁺,导致Mo S₂电极呈现出较低的放电比容量。本研究通过一种简单的氨水辅助水热法制备了NH₄⁺扩层的二硫化钼(Mo S₂-N)电极,氨水分解产生的氨气在促进硫代乙酰胺水解和提供还原性S^2–的同时,还会产生大量NH₄⁺作为插层离子,将Mo S₂的层间距由0.62 nm扩展至0.92 nm,进而大大降低了Zn²⁺嵌入能垒(改性电极的电荷转移电阻R_ct低至35?)。当电流密度为0.1 A·g^–1时,Mo S₂-N电极的初始放电比容量相比未扩层的Mo S₂     

分子动力学模拟不同入射角度的SiF3+对SiC表面的作用

采用分子动力学模拟方法研究了300K入射能量150eV时,以不同角度(5°、30°、60°和75°)入射的SiF3+与SiC表面的相互作用过程。模拟中使用了用于Si-F-C体系的Tersoff-Brenner势能函数。模拟结果显示,入射SiF3+与SiC表面相互作用后会分解,分解率随着入射角度的增加而减小。分解产物除少量散射外,大部分会沉积在SiC表面,Si和F在SiC表面的平均饱和沉积量随入射角度的增加而减少。随着SiF3+不断轰击SiC表面,SiC表面会形成Si-F-C反应层,且反应层厚度随着入射角度的增加而减少。同时发现SiC中的Si原子较C原子更容易被刻蚀,与实验结果一致。当刻蚀达到稳定,入射角度为5°、30°、60°和75°时,C的刻蚀率分别约为0.026、0.038、0.018、0.005,Si的刻蚀率分别约为0.043、0.051、0.043和0.023。各入射角度下,产物分子种类主要为F、SiF和SiF2。F和SiF产物量随入射角度增加而增加,而SiF2产量随入射角度增加而减少。在入射角度等于5°和30°时,SixFyCz是主要的含C产物;而在入射角度等于60°和75°时,CF是主要的含C产物。在入射角度等于5°和30°时,SiF2是主要的含Si产物;在入射角度等于60°和75°时,SiF是主要的含Si产物。刻蚀主要通过化学增强的物理溅射进行。