Synthesis and investigation of magnesium chromium spinel

Magnesium chromium spinel nanopowders have been synthesized through cocrystallization. The formation and structural perfection of the MgCr₂O₄ crystalline phase have been investigated in the temperature range 500–1400°C. The average size of crystals of the MgCr₂O₄ phase has been determined at different temperatures. The influence of the temperature, porosity, and reducing medium on the electrical conductivity of the MgCr₂O₄ phase has been studied.     

尖晶石型锰酸锂锂离子筛的合成研究

为了比较不同合成方法对锰酸锂(Li4Mn5O12)锂离子筛的结构、饱和交换容量和分离因子的影响,采用低温固相反应法和溶胶-凝胶法合成了锰酸锂锂离子筛,并用X射线衍射(XRD)表征了所得材料的结构.结果表明,低温固相反应法和溶胶-凝胶法制备的锰酸锂及其离子筛均为尖晶石结构.低温固相反应法合成的锂离子筛,其锂离子饱和交换容量为16.06 mg/g(2.31 mmol/g)、分离因子αLiNa为23;溶胶-凝胶法合成的锰酸锂锂离子筛,其锂离子饱和交换容量为26.39 mg/g(3.80 mmol/g),分离因子αLiNa为216,优于低温固相反应法所得锂离子筛的性能.     

The role of liquid ion exchange in the processing of complex solutions

The use of liquid ion exchange in the processing of complex solutions is described, with particular reference to the development and economics of the process for co-extraction and selective stripping of copper and nickel.     

Study of the changes in the structure and optical properties of MgxCo1-xCr2-yAlyO4 spinel caused by A/B site ion substitution

In this work, nanosubmicron blue-green pigment powder based on the composition of Mg_xCo_1-xCr_2-yAl_yO₄（0 = x ≤ 1, 0 = y ≤ 2）was prepared by a gel casting method. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Rietveld refinement with GSAS (General Structure Analysis System), and UV–Vis absorption spectroscopy were used to study the phase composition, grain size, morphology, cation distribution in the crystal structure and spectral absorption of the samples. Colour parameters were also studied by using a colour measurement spectrophotometer. The studies demonstrate that the distribution of cations in the crystal structure is disordered and that divalent and trivalent cations are mixed to occupy tetrahedral and octahedral sites. Furthermore, the substitution of ions at the A/B site leads to a change in the cation distribution ratio at the tetrahedral and octahedral sites. With increasing Mg²⁺ doping concentration, the inversion parameter of the spinel increases, while with increasing Al³⁺ doping concentration, the inversion parameter of the spinel decreases. In addition, changes in the calcining atmosphere lead to a change in the oxygen vacancy content in the structure. Under the condition of a reductive atmosphere, the oxygen vacancy content significantly increases, and the inversion parameter also increases. The colour difference for the synthesized Mg_xCo_1-xCr_2-yAl_yO₄ spinel powder is related to the proportion of chromophore ions occupying tetrahedral and octahedral sites and the number of oxygen vacancies.     

Trigonal distortion of water octahedron surrounding trivalent chromium ion

Mixed crystals of ammonium aluminium alum and thallium aluminium alum are grown with various concentrations of ammonium and thallium with chromium as dopant. The optical absorption spectra and EPR spectra are recorded and analysed. Variation of zero field splitting parameter (D) with concentration of thallium is studied in EPR spectra. The increase in the value of D with increasing concentration of thallium atoms is predicted to be due to the trigonal distortion caused by these atoms in the co-ordinating water octahedron. These results are also supported by the splitting of one of the bands in the optical absorption spectrum which is attributed to the trigonal distortion and increase in splitting with increase of thallium atom concentration.     

铬离子印迹聚合物制备及应用研究进展

离子印迹聚合物对目标金属离子具有特异性识别功能,有利于选择性吸附和分离水溶液中的铬离子。本文介绍了制备Cr(III)和Cr(VI)离子印迹聚合物的方法,并阐述了国内外铬离子印迹聚合物制备以及在对水中铬离子检测与吸附去除应用中的研究进展。对铬离子印迹技术的研究现状和存在问题进行深入分析,对其发展趋势和应用前景进行展望。     

The effect of composition and synthesis conditions on the structure of cobalt-bearing pigments of the spinel type

The results of producing cobalt-bearing spinels of a blue-sky to blue color range by self-propagating high-temperature synthesis (SHS) are described. The effect of the conditions of synthesis and the mixture composition on the structure of compounds obtained is demonstrated. The SHS method makes it possible to obtain spinels that can be used as ceramic pigments.     

离子色谱法测定镀液中的六价铬离子

建立了用单柱阴离子色谱测定镀液中六价铬离子的方法.采用HPIC-CS5阴离子交换柱,以5.0 mmol/L碳酸钠和1.0 mmol/L碳酸氢钠的混合溶液作为流动相,电导检测器在20 min内完成镀液中六价铬的测定.该法具有良好的线性(相关系数约为0.996)和重复性(相对标准偏差小于5％),回收率在93％ ～107％的...     

杂质对三价铬电沉积非晶态Fe-Cr镀层的影响

从三价铬镀液中电沉积非晶态Fe-Cr合金镀层,电沉积过程中的副产物Cr6 和Fe3 的存在影响镀层电沉积过程,通过梯形槽实验发现这些杂质离子会使镀层质量下降,漏镀的范围变大.加入一定量的抗坏血酸C6H8Ob还原剂,可有效地减少Cr6 和Fe3 的量,得到优良的镀层.     

The role of ion—ion interactions in the electrical double layer: symmetrical electrolytes containing equal size ions

A simple model for the ion distribution at the metal—electrolyte interface is presented, based on charge redistribution in response to a change in potential across the interface. In this model, it is not necessary to subdivide the interface along the lines of the traditional approach to the double layer problem. The most important feature of our appraoch is an emphasis on ion—ion repulsion within a thin region of reduced (macroscopic) permittivity parallel to the metal surface.     

Simulation of phase diagrams of oxychromites with a spinel structure

Phase diagrams of oxychromites with a spinel structure are described in the context of the Landau phenomenological theory of phase transitions. As an approximation of the thermodynamic potential of the sixth degree with respect to components of the order parameter, the implementation conditions of each type of phase diagrams are found. Equations for calculation of coordinates of tricritical and triple points are obtained. A qualitative agreement of the theoretically calculated results of the phase diagrams and experimental phase diagrams of some oxychromites with a spinel structure is observed.     

The role of Co ion substitution in SnFe2O4 spinel ferrite nanoparticles: Study of structural,vibrational, magnetic and optical properties

In order to accurately investigate the effect of cobalt substitutions in tin ferrite (SnFe₂O₄) properties, we prepared Co_xSn_1-xFe₂O₄ nanoparticles for different Co concentrations, x?=?0.0, 0.25, 0.50, 0.75, and 1.00 using a simple co-precipitation method. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and diffuse reflectance spectra (DRS) are used to study of structural, magnetic, morphology, and optical properties. The XRD and FTIR results confirmed the formation of cubic spinel structure. The lattice parameter and unit cell volume of tin ferrite nanoparticles were found to increase by entering and increasing Co⁺² content in 0.25, and then significantly decrease for higher contents. In accordance with the XRD results, a slight shift in main band υ₁ (${\mathit{Fe}}_{\mathrm{tetra}}^{+3}?O)$ to lower wavenumber and then to higher wavenumber were observed in the IR spectra of Co content x?<?0.25 and x?>?0.25, respectively. In turn to, saturation magnetization, remanent magnetization and anisotropy constant of SnFe₂O₄ nanoparticles were gradually increased for x?=?0.50 and then decreased for x?>?0.50.     

Ti33 Ru33 Co33尖晶石型钛阳极的制备

采用溶胶－凝胶法制备了Ｔｉ３３Ｒｕ３３Ｃｏ３３尖晶石型钛阳极,并对涂层运用ＤＴＡ,ＸＲＤ,ＴＥＭ,ＳＥＭ等手段进行了测试,研究结果表明：涂层为尖晶石结构,形貌呈块状;钛阳极涂层烧结温度为３２０℃,涂层晶粒小于１０ｎｍ。     

The role of mass transfer in the electrolytic reduction of hexavalent chromium at gas evolving rotating cylinder electrodes

The rate of electrolytic reduction of hexavalent chromium from acidic solution at a hydrogen-evolving rotating cylinder lead cathode was studied under conditions of different current densities, Cr⁶⁺ concentrations and rotation speeds. The rate of the reaction was found to follow a first order rate equation. The specific reaction rate constant was found to increase with increasing rotation speed until a limiting value was reached with further increase in rotation speed. Mechanistic study of the reaction has shown that at relatively low rotation speeds the reduction of Cr⁶⁺ is partially diffusion controlled, at higher speeds the reaction becomes chemically controlled. The limiting specific reaction rate constant was related to the operating current density by the equationK=0.044i ^1.385. The current efficiency of Cr⁶⁺-reduction was measured as a function of current density, initial Cr⁶⁺ concentration and rotation speed. Possible practical applications are discussed.Nomenclature A electrode area (cm²) - a, b constants in Equations 5 and 13, respectively - C bulk concentration of Cr⁶⁺ at timet(M) - C _o initial concentration of Cr⁶⁺ (M) - C _i interfacial concentration of Cr⁶⁺ (M) - d cylinder diameter (cm) - D diffusivity of Cr⁶⁺ (cm² s^–1) - e _o standard electrode potential (V) - F Faraday's constant (96 487 C) - current consumed in hydrogen discharge (A) - i current density (A cm^–2) - I cell current (A) - K _l mass transfer coefficient (cm s^–1) - K _r mass transfer coefficient due to cylinder rotation (cm s^–1) - K _o natural convection mass transfer coefficient (cm s^–1) - K _g mass transfer coefficient due to hydrogen stirring (cm s^–1) - K ₂ specific reaction rate constant (cm s^–1) - K overall rate constant (cm s^–1) - m theoretical amount of Cr⁶⁺ reduced during electrolysis (g) - P gas pressure (atm) - R gas constant (atm cm³ mol^–1 K^–1) - T temperature (K) - t time (s) - V linear speed of the rotating cylinder (cm s^–1) - hydrogen discharge rate (cm³ cm^–2 s^–1) - V _s solution volume (cm³) - z electrochemical equivalent (g C^–1) - Z number of electrons involved in the reaction - Re Reynolds number (Vd/v) - Sh Sherwood number (K _r d/D) - Sc Schmidt number (v/D) - rotation speed (r.p.m.) - kinematic viscosity (cm² s^–1)     

The role of water fluid in the formation of fine-crystalline oxide structure

This paper reports on investigations of the kinetics and mechanism of the synthesis of simple fine-crystalline oxides from solid-phase precursors in sub- and supercritical water fluid (SCWF). The rate of the processes strongly depends on the water vapor pressure. X-ray analysis, mass-spectrometry and IR-spectrometry of products obtained during synthesis in water fluid reveal the presence of an intermediate hydrated solid phase. Thus, the synthesis of quartz and corundum in SCWF runs through the stage of the formation of hydrated intermediates. The main type of defects in crystals synthesized in SCWF is oxygen vacancies produced during the dehydroxylation of an intermediate structure when forming the final product. By varying the parameters of the water fluid (P, T), it is possible to influence the local processes of crystal build-up and thus to produce crystals of various size, habitus and degree of perfection.     

花生壳改性处理含铅废水及吸附机理研究

通过对花生壳改性处理模拟含铅废水,增强对铅离子的吸附能力,结果表明,最佳改性方法是花生壳在0.015 mol/L高锰酸钾中搅拌改性4 h。改性前后花生壳的IR图谱发现吸附位点种类没有增加,但是数量明显增加;BET比表面积测试结果表明,改性后花生壳的比表面积增加了78%。在初始条件为50 m L含Pb2+100 mg/L模拟含铅废水时,最佳的吸附条件为0.2 g改性花生壳在含铅废水中吸附2 h,Pb2+除去率为99.48%,较未改性的花生壳提高了42.63%。吸附机理研究表明,采用Lagergren准二级动力学模型和Langmuir等温吸附模型可以准确描述吸附行为,拟合实验数据平衡吸附量为24.93 mg/g,与实验结果一致。