Influence of Cd and Cr substitutions on the magnetization and permeability of magnesium ferrites

Magnetization and permeability of polycrystalline ferrites with general formula Cd_xMg_1−xFe_2−yCr_yO₄ (x=0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0, 0.05 and 0.10) were studied. Study of saturation magnetization reveals that the Neel's two-sublattice model exists upto x=0.4, for y=0, 0.05 and 0.1 and a three-sublattice model (YK-model) is predominant for x>0.4 and y=0, 0.05 and 0.10. The saturation magnetization and magnetic moment were found to decrease with the increase in Cr³⁺ contents, which is attributed to the dilution of B–B site interaction. Variation of initial permeability with temperature revealed the long-range ferromagnetic ordering in the compounds with x=0.4. The sample with x?0.4 and y=0, 0.05 and 0.10 showed peaking behavior near Curie temperature, which is attributed to the decrease of anisotropy constant K₁ to zero. Low-frequency dispersion of initial permeability suggests domain wall displacement. Addition of Cd²⁺ resulted in a sharp decrease in Curie temperature. With the addition of Cr³⁺, initial permeability was found to decrease.     

一次消解测定蔬菜中多种重金属的简捷方法

针对一般实验室检测人员少,检测任务重的问题,研究了蔬菜通过一次湿化消解后,消解液可以测定多种重金属元素的方法,大大提高了效率,减轻了工作量.     

Synthesis and electrochemistry of Group 6 tetracarbonyl (N,N′-bis(ferrocenylmethylene)ethylenediamine)metal(0) complexes

Thermal substitution reaction of Cr(CO)₄(η^2:2-1,5-cyclooctadiene), Mo(CO)₄(η^2:2-norbornadiene), and W(CO)₅(η²-bis(trimethylsilyl)ethyne) with N,N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO)₄(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO)₅(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO)₄(bfeda). The electrochemical behavior of the M(CO)₄(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH₂Cl₂ solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO)₄(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO)₄(bfeda) and W(CO)₄(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom.     

Thermoluminescence of Chromium Doped Cd2Nb2O7 Crystals

The exposure of the Cd₂Nb₂O₇:Cr crystal to monochromatic light with wavelength shorter than 600 nm at 12 K decreases the Cr^3? photoluminescence emission and allows us to observe thermoluminescence within 60–200 K during subsequent heating of the crystal at a rate of 0.077 K/s. The glow curve of thermoluminescence revealed a rather complex structure with two pronounced intensive glow peaks at 91 and 180 K and four rather weak peaks at 99, 117, 132, and 155K. An analysis of the glow peaks by “an initial rise” gave evidence of many various charge carrier traps with activation energies from 150 to 470 meV. Since a comparison of the thermoluminescence and photoluminescence emission spectra showed that these spectra are identical, it was concluded that the thermoluminescence glow peaks are associated with thermal release of charge carriers from shallow traps followed by Cr^4?→Cr^3?(²E) and/or Cr^2?→Cr^3?(²E) charge capture and ²E→⁴A₂ radiative decay of Cr^3?(²E) ions.     

Cathodoluminescence from deformed doped MgO crystals

The cathodoluminescence (CL) from indented Fe doped MgO single crystals has been studied with the scanning electron microscope and the results have been compared with the CL from undoped crystals. As in the undoped crystals, the iron doped crystals show in the deformed regions an enhanced luminescence emission but it has been found that iron acts as a quencher of luminescence. The results indicate that in the blue emission of the deformed crystals there is not a noticeable contribution of iron. From the evolution of CL with the irradiation time in the electron microscope it is concluded that the total Fe content influences the CL emission more than the Fe³⁺ content.     

Corrosion inhibition of ammonium molybdate for AA6061 alloy in NaCl solution and its synergistic effect with calcium gluconate

The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10^?4 mol.l^?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

吸光度比值-导数光谱法同时测定铜(Ⅱ)和铬(Ⅲ)的研究

提出了运用吸光度比值-导数光谱法同时测定Cr(Ⅲ)与Cu(Ⅱ)含量的新方法。在pH 5.7的HAc-NaAc的缓冲溶液中,Cr3+,Cu2+与铬天青S(CAS)和溴化十六烷基三甲胺(CTMAB)可分别形成蓝色三元络合物。其摩尔吸光系数分别为2.52×105 L·mol-1·cm-1和1.01×105 L·mol-1·cm-1。Cu2+和Cr3+的浓度分别在0.08～1.2 μg·mL-1和0.05～0.52 μg·mL-1范围内符合比尔定律,其检测限分别为0.014和0.013 μg·mL-1。此方法应用于环境水中Cr(Ⅲ),Cu(Ⅱ)的同时测定,取得了满意的结果。     

Photoemission study of the modification of the electronic structure of transition-metal overlayers on TiO2 surfaces II. Cr on TiO2(0 0 1)

The electronic states of the Cr overlayers on TiO₂(0 0 1) surfaces have been investigated using angle-resolved and resonant photoemission spectroscopy with synchrotron radiation. At lower coverages, Cr deposition on TiO₂(0 0 1) creates two well separated in-gap emissions due to the formation of surface Ti³⁺ (3d¹) ions and Cr³⁺ (3d³) ions. At higher coverages, the in-gap emission is developed into the 2-peak-structure emission of Cr 3d character. The corresponding state is considered to be of metallic nature from the viewpoint of the high ability of oxygen adsorption, but has no Fermi edge, indicating a possibility of forming small Cr clusters on TiO₂(0 0 1) at this stage.     

NaLa(MoO4)2∶Eu3+的水热调控合成与发光特性研究

采用水热法合成了不同粒径的NaLa(MoO₄)₂∶Eu³⁺微晶.通过调节乙二醇浓度和反应时间,研究了NaLa(MoO₄)₂∶Eu³⁺微晶的形貌演变过程,在水热条件下180 ℃反应16 h获得了均一梭子形NaLa(MoO₄)₂∶Eu³⁺微晶,其晶粒长度约为2.0 μm.荧光光谱分析表明,Eu³⁺取代了NaLa(MoO₄)₂中La³⁺的格位, Eu³⁺在613 nm处红光发射(⁵D₀–⁷F₂跃迁)的浓度猝灭机理是电偶极-电四极相互作用,并发生了Eu³⁺( ⁵D₁ ) + Eu³⁺(⁷F₀ )→ Eu³⁺( ⁵D₀ ) + Eu³⁺(⁷F₃) 交叉弛豫,由此导致浓度猝灭. 关键词： 钼酸盐 水热法 稀土离子 发光