在LiCl-KCl-ZnCl_2熔盐体系中电化学共还原提取钕

针对镧系元素钕,本文通过循环伏安、开路计时电位、方波伏安等方法研究了773 K时Nd(III)在钼电极上在LiCl-KCl-ZnCl2熔盐体系中的电化学行为及Zn-Nd合金的形成过程.结果表明:在LiCl-KCl-ZnCl2熔盐中,Nd(III)在预先沉积的Zn阴极上欠电位沉积形成三种Zn-Nd金属间化合物.基于电化学行为研究,采用恒电位电解提取Nd并用方波伏安曲线测量来检测Nd(III)离子浓度的变化,然后通过电解前后Nd(III)离子浓度变化评估了Nd的电解提取效率.实验结果表明:-1.84 V恒电位电解进行50 h后,Nd(III)离子浓度接近于零,提取效率为99.67%.在973 K时通过恒电流电解提取Nd并获得了Zn-Nd合金,通过X射线衍射(XRD)和扫描电子显微镜(SEM)附带能量散射谱(EDS)对合金的相组成和微观形貌进行了分析.XRD分析表明在Zn-Nd合金中存在Nd2Zn17,LiZn和Zn相,EDS能谱分析表明Nd在合金中的原子分数高达14.99%.     

Oxygen Reduction on Amalgamated Platinum Electrodes Coated with Monolayers of Cetyl Alcohol and Stearic Acid

Oxygen reduction on an amalgamated platinum electrode with a monolayer of cetyl alcohol or stearic acid is studied. It is shown that the process proceeds inside the monolayer, most probably, at a certain distance from the metal; an electron is transferred to the reagent by the superexchange mechanism. The process characteristics depend on competition between several factors: the electron transfer distance, the potential drop between the electrode and the reagent in a given site in the monolayer, and the hydrogen ion concentration distribution across the film. The penetration of H⁺ inside the film appears to be responsive to the monolayer structure.     

Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

We present a review of the structural properties of LiFePO₄. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries.     

Electropolymerized Pyrrole‐Substituted Manganese Phthalocyanine Films for the Electroassisted Biomimetic Catalytic Reduction of Molecular Oxygen

We report for the first time on the electroassisted biomimetic activation of molecular oxygen by a newly prepared electropolymerized polypyrrole‐manganese phthalocyanine film. The prepared films and their intervention in the electroassisted catalytic reduction of molecular oxygen were analyzed by cyclic voltammetry and UV‐visible spectrophotometry on optically transparent electrodes. The obtained results demonstrate the probable existence of the key‐steps responsible for the suggested formation of the highly reactive manganese oxo intermediate.     

Preparation of Y2Ba4Cu7O15-δ Superconductor without High Oxygen Pressure

The synthesis of bulk Y₂Ba₄Cu₇O_15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y₂Ba₄Cu₇O_15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y₂Ba₄Cu₇O_15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described.     

Oxidation of mandelic acid derivatives catalysed by Bi(0)/O2 systems: mechanistic considerations

Mandelic acid and some aryl substituted derivatives were oxidised under molecular oxygen and a catalytic amount of Bi(0). The corresponding aldehydes and/or the carboxylic acids were obtained selectively depending on the nature of the substituent. Aldehydes and α-keto acids were oxidised under the same Bi(0)/O₂ system and α-keto acids were proposed as intermediates in the formation of benzoic acid derivatives.     

Syntheses and characterization of ferrocenylthiocarboxylate-containing coordination compounds for nonlinear optics

Four metal-organic coordination compounds containing ferrocenylthiocarboxylate components, [Cd₂(η²-SOCFc)₂(η¹-μ₂-SOCFc)₂(4,4′-bpy)]_n (1), [Cd(SOCFc)₂(tmp)]_n (tmp = 4,4′-trimethylene-dipyridine) (2) [Zn(SOCFc)₂(2,2′-bpy)] (3), and {[Hg(SOCFc)₂(phen)] · (0.5CH₃OH)} (4) (Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)), have been prepared in search of good nonlinear optical (NLO) materials. Investigation of the NLO properties shows that Hg-containing compound 4 exhibits very strong third-order NLO absorptive and refractive effects. The NLO absorptive coefficient α₂ value (2.11 × 10⁻¹⁰ m W⁻¹) is larger than those of all the reported ferrocenylcarboxylate-containing coordination compounds and comparable to the well-performing Hg-containing complexes. Additionally, we further analyzed their NLO behaviors through studying electrochemical properties of the four compounds.     

How Is Oxygen Incorporated into Oxides? A Comprehensive Kinetic Study of a Simple Solid‐State Reaction with SrTiO3 as a Model Material

The kinetics of stoichiometry change of an oxide--a prototype of a simple solid-state reaction and a process of substantial technological relevance--is studied and analyzed in great detail. Oxygen incorporation into strontium titanate was chosen as a model process. The complete reaction can be phenomenologically and mechanistically understood beginning with the surface reaction and ending with the transport in the perovskite. Key elements are a detailed knowledge of the defect chemistry of the perovskite as well as the application of a variety of experimental and theoretical tools, many of them evolving from this study. The importance of the reaction and transport steps for (electro)chemical applications is emphasized.     

Photochemically initiated oxidative carbon-carbon bond-cleavage reactivity in chlorodiketonate Ni(II) complexes

Three mononuclear Ni(II) complexes containing a 2-chloro-1,3-diketonate ligand and supported by the 6-Ph(2)TPA chelate, as well as analogues that lack the 2-chloro substituent on the β-diketonate ligand, have been prepared and characterized. Upon irradiation at 350 nm under aerobic conditions, complexes containing the 2-chloro-substituted ligands undergo reactions to generate products resulting from oxidative cleavage, α-cleavage, and radical-derived reactions involving the 2-chloro-1,3-diketonate ligand. Mechanistic studies suggest that the oxidative cleavage reactivity, which leads to the production of carboxylic acids, is a result of the formation of superoxide, which occurs through reaction of reduced nickel complexes with O(2). The presence of the 2-chloro substituent was found to be a prerequisite for oxidative carbon-carbon bond-cleavage reactivity, as complexes lacking this functional group did not undergo these reactions following prolonged irradiation. The approach toward investigating the oxidative reactivity of metal β-diketonate species outlined herein has yielded results of relevance to the proposed mechanistic pathways of metalloenzyme-catalyzed β-diketonate oxidative cleavage reactions.     

The detection of oxygen in magneto-optical layers with SIMS

The detection of oxygen in magneto-optical layers is of fundamental importance for the characterization of the stability of RE-TM material. The magnetic properties are directly influenced by oxide formation. Oxygen depth profiles are carried out by using the SIMS technique. A comparison with magnetic measurements showed a clear conformity. We were able to study the oxidation behaviour of various layers at room temperature and at higher values up to 250° C for several hours. It could be shown that aluminum is a successful material for the protection of RE-films against oxidation. The difficulties of translating SIMS counting rates into concentration values were overcome by using EPMA. Specially prepared reference samples were measured by this technique and could then be used as standard samples for SIMS.