ESR examination of thermally treated Fe (III) coprecipitated with Al(OH)3·nH2O

Journal of Materials Science Letters -     

球形尖晶石LiMn2O4的制备及性能

通过氧化还原法在室温下制备出球形MnO2前驱体,以LiOH·H2O为锂源,按照一定锂锰摩尔比混合,在750℃下焙烧8h,得到球形尖晶石LiMn2O4.采用X射线衍射和扫描电镜对MnO2和LiMn2O4进行了表征,并对LiMn2O4样品做了充放电性能及循环性能测试.结果表明:合成的样品以球形颗粒存在,粒度大小均匀,分散性和流动性好;首次充放电比容量分别为130.5和128.2 mAh·g-1,充放电效率为98.2%,50次循环后容量保持率为90%,球形LiMn2O4具有较高的比容量和优良的循环性能.     

尖晶石结构Ni掺杂ZnFe2O4纳米颗粒的性能表征

利用水热法成功合成了纯ZnFe2O4和不同含量Ni掺杂Zn1-xNixFe2O4纳米颗粒。采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、选区电子衍射(SAED)、X射线能量色散分析(XEDS)、紫外可见吸收光谱(UV-Vis)、傅里叶变换红外光谱(FT-IR)和振动样品磁强计(VSM)等测试技术研究掺杂浓度对Zn1-xNixFe2O4(x=0,0.1,0.3,0.5)样品的晶体结构、形貌、光学性能和磁学性能的影响。结果表明:所制备的Zn1-xNixFe2O4纳米颗粒结晶良好,Ni2+以替代Zn2+的形式掺杂到ZnFe2O4晶格中,生成立方尖晶石结构ZnFe2O4。随着Ni含量的增加,晶粒尺寸增大,晶格常数发生收缩。样品的形貌呈不规则的椭球形,且颗粒大小比较均匀。红外光谱的吸收峰位置并没有随Ni掺杂浓度的增加而变化。Zn1-xNixFe2O4纳米晶的光学带隙随Ni掺杂浓度增加而增大,与相应块体相比发生蓝移。在室温下,纯ZnFe2O4纳米晶呈现超顺磁性,掺杂样品具有明显的铁磁性。     

纳米微孔杂多化合物Na[Fe2(O2H3)Mo2O8](Ⅰ)和(NH4)[Fe(MoO4)2](Ⅱ)的结构特征

通过采用水热合成法得到了二种具有纳米筛孔的氧簇化合物Na[Fe2(O2H3)Mo2O8](Ⅰ)和(NH4)[Fe(Mo O4)2](Ⅱ).晶体(Ⅰ)属于单斜晶系,空间群为C2/m,晶胞参数为:a=9.5450(17),b=6.4381(9),c=0.76405(12)nm;β=116.128(4),Z=2,R1=0.0219,Rw=0.0756.晶体(Ⅱ)属于正交晶系,空间群为Pnma,晶胞参数为:a=1.4782(3),b=0.56774(11),c=0.87653(18)nm;Z=4,R1=0.0212,Rw=0.0513.     

Cellulose-precursor synthesis of nanocrystalline Co0.5Cu0.5Fe2O4 spinel ferrites

Nanocrystalline Cu_0.5Co_0.5Fe₂O₄ powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.     

Synthesis and characterization of MgAl2O4 spinel by PVA evaporation technique

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

尖晶石LiMn2O4表面包覆MgO及其性能

Mn^2 在电解液中的溶解是引起LiMn2O4正极材料性能恶化的重要原因。用沉淀法在LiMn2O4表面包覆一层Mg(OH）2,再进行热地理,制备由表面包覆MgO的LiMn2O4。用X光电子能谱、扫播电镜和X射线衍射对包覆前后的LiMn2O4的结构进行了表征。充放电测试结果表明．经表面修饰处理后LiMn2O4的循环及高温性能明显改善。研究结果表明表面修饰北理可以抑制正极材料和电解液之间的相互作用．是改善锂离子二次电池正极材料性能的有效途径。     

Effects of copper content on the structural and magnetic properties of spinel (Co,Cu)Fe2O4 ferrites

Spinel Co–Cu ferrites with the nominal composition Co_1?x Cu _x Fe₂O₄ ferrites (x = 0.0–0.4 with steps of 0.1) were prepared by a chemical coprecipitaiton and sintering process, and their structural and magnetic properties were studied by using XRD, TGA–DTA, FTIR, SEM and VSM analyses. All the specimens prepared are single phase after sintering at 900 °C for 5 h, and nearly no change of lattice parameter is found. The study of grain size shows that suitable amount of Cu substitution is favorable for the growth of grains, while too much Cu substitution inhibits the growth of grains instead. Also found is that with the increase of x, the saturation magnetization decreases continuously from 76.6 (x = 0.0) to 59.0 emu/g (x = 0.4), while the coercivity exhibits a first decreasing but then increasing tendency.     

Effective removal of Zn (II) ions from aqueous solution by the magnetic MnFe2O4 and CoFe2O4 spinel ferrite nanoparticles with focuses on synthesis,characterization, adsorption,and desorption

In this study, the MnFe₂O₄ and CoFe₂O₄ spinel ferrites nanoparticles were synthesized via a practical co-precipitation route to investigate the zinc removal from aqueous solution. The synthesized magnetic adsorbents were characterized by XRD, VSM, FE-SEM, BET, EDS, and DLS analyses. The synthesized adsorbents had a diameter range of 20–80 nm. The specific surface areas of adsorbents were found to be 84.5 and 50.4 m²/g for MnFe₂O₄ and CoFe₂O₄, and the saturation magnetization were 61.39 and 37.54 emu/g, respectively. The effects of initial pH, contact time, metal ion concentration, and temperature on Zn (II) adsorption were precisely investigated. These nanoparticles could remove Zn (II) by following the Langmuir isotherm model at optimum pH = 6, with the high adsorption capacities of 454.5 and 384.6 mg/g for MnFe₂O₄ and CoFe₂O₄, respectively. The results of kinetics studies were well fitted by pseudo-second-order, with the determination coefficients of 0.999 for both adsorbents. The thermodynamics studies showed that the zinc (II) adsorption was an exothermic and spontaneous process. Furthermore, the reusability and the desorption capability of adsorbents were also investigated.     

Magnetic SiO(2)/Fe(3)O(4) colloidal crystals

We proposed a novel technique to fabricate colloidal crystals by using monodisperse SiO(2) coated magnetic Fe(3)O(4)(SiO(2)/Fe(3)O(4)) microspheres. The magnetic SiO(2)/Fe(3)O(4) microspheres with a diameter of 700?nm were synthesized in the basic condition with ferric sulfate, ferrous sulfate, tartaric acid and tetraethyl orthosilicate (TEOS) in the reaction system. Monodisperse SiO(2)/Fe(3)O(4) superparamagnetic microspheres have been successfully used to fabricate colloidal crystals under the existing magnetic field.     

Mössbauer effect characterization and thermal transformations of Fe(III) ions co-precipitated with praseodymium trihydroxide

Mössbauer studies at+27 and–196° C on 5 wt % Fe(III) ions co-precipitated with praseodymium trihydroxide and subjected to annealing for 24h at 100, 350, 600, 725, 825 and 1100° C are reported. Variations in Mössbauer spectral parameters and the results of thermal analysis, infra-red spectroscopy, electron microscopy and X-ray diffraction (XRD) studies on the samples have been used to follow and to gain insight into the nature of thermal and microstructural processes that occur during phase transitions. In the co-precipitate, Fe ions exist as ferric oxide hydrate gel-like species. In samples annealed at 100° C Fe ions exhibit an increase in dispersion strengthening in the lattice while in samples annealed at 350° C they become somewhat labile due to disruption of lattice planes on dehydroxylation. In samples annealed at 600° C magnetically split sixline Mössbauer spectra are observed, which in agreement with XRD analysis and electron paramagnetic resonance studies indicate the precipitation of PrFeO₃ microphases in Pr₆O₁₁. Annealing to higher temperatures finally leads to a pronounced agglomeration of iron microphases and the establishment of a better crystallized host lattice.     

Cation Distribution and Magnetic Interactions in Zn-Substituted Fe(Cu)Fe2O4 Ferrites

The effect of Zn doping on magnetic properties of Fe₃O₄ and CuFe₂O₄ ferrite spinels has been studied. The general expression of saturation magnetization, the critical temperature and Curie constant (C) are obtained by the mean field theory (MFT). By considering the high-temperature series expansions (HTSE) theory and the mean field approximation for the Néel??s two-sublattice noncollinear model, we obtained the magnetic phase diagrams of Zn _x Fe_1?x Fe₂O₄, and Zn _x Cu_1?x Fe₂O₄. The Bohr magnetron is obtained for two systems. The central critical exponent ?? associated with magnetic susceptibility for two systems is obtained.