Magnetic and Rheological Characterization of Fe3O4 Ferrofluid: Particle Size Effects

Magnetite particles of different diameters were synthesized by chemical co-precipitation technique and the same are dispersed in dodecane to prepare a magnetic fluid. The results of X-ray diffraction, magnetization measurements, ac susceptibility and viscosity measurements are analyzed and discussed in the text.     

新型螯合磁性纳米Fe3O4的制备及其性能研究

采用共沉淀法制备了磁性四氧化三铁(Fe3O4)纳米粒子,并通过硅烷偶联剂对其表面进行改性,进一步在其表面偶联修饰氨基硫脲,制备了螯合磁性纳米Fe3O4粒子。利用广角X射线衍射仪(WAXD)、红外光谱仪(FTIR)、分光光度计等对磁性纳米粒子的结构和性能进行了表征。结果表明,纳米Fe3O4为反尖晶石结构,通过偶联修饰可以实现氨基硫脲在纳米粒子表面的化学改性。螯合磁性纳米粒子具有良好的分散性和磁响应性,且对多种金属离子(Pb2+、Hg2+、Zn2+、Cd2+)具有良好的螯合效果。     

Fe3O4@Au纳米材料的制备和光谱性质

采用共沉淀法制备了Fe3O4纳米颗粒,并以其为晶种利用晶种生长法制备了Fe3O4@Au磁性复合纳米粒子。吸收光谱显示Au壳层成功包覆在了Fe3O4纳米核的表面。以结晶紫为探针分子的表面增强拉曼散射（SERS）光谱展示了Fe3O4@Au良好的SERS活性。     

Analysis of Particle Size Distribution by Particle Tracking

Particle tracking is performed using a combination of dark field or fluorescence video microscopy with automatic image analysis. The optical detection together with the image analysis software allows for the time resolved localization of individual particles with diameters between 100 and 1000 nm. Observation of their Brownian motion over a set of time intervals leads to the determination of their mean square displacements under the given room temperature and viscosity. Hereby, the radii of a set of particles visible within a given optical frame are derived simultaneously. Rapid data analysis leads to reliable particle size histograms. The applicability of this method is demonstrated on polystyrene latices and PMMA nanospheres with radii between 51 nm and 202 nm.     

Determination of Particle Size Distribution and Electrokinetic Properties with the AcoustoSizer in Comparison with Other Methods

The characterization of suspensions in process concentration is an important task for the optimization of handling and product properties. Only very few instruments are available. The AcoustoSizer (ACS) (Colloidal Dynamics PTY Ltd.) uses the so-called electrokinetic sonic amplitude (ESA) for particle size and zeta potential determination. In this work, the results obtained at moderate concentrations were compared with results of other instruments mostly working with dilute suspensions. For the electrokinetic investigations three methods (beside the ACS) were used: electroacoustics (ESA8000, Matec Applied Sciences), microelectrophoresis (Zetamaster, Malvern Instruments) and streaming current measurements (Particle Charge Detector PCD 03-pH, Miitek). For particle size determination different measuring techniques were applied: laser diffraction spectroscopy (Mastersizer S, Malvern Instruments), dynamic light scattering (Ultra Fine Particle Analyser, Leeds and Northrup), sedimentation analysis (Sedigraph 5000 D, Micromeritics) and scanning electron microscopy. Mainly three powders were used in the investigations: Monospher M1200 silica (Merck), Selectipur titania (Merck) and Aluminiumoxid C alumina (Degussa). The agreement between the different methods for both particle size and zeta potential measurements was excellent. Especially for the electrokinetic investigations, careful sample preparation is needed. The procedure must not change the equilibria determining the physical and chemical state of the suspension.     

Distribution and valence of the cations in the spinel system Fe3O4-Fe2VO4

The Mössbauer spectra of the solid solution Fe[Fe_xV_2–x]O₄ within 1.0×2.0 consist of two sets of sextets corresponding to A- and B-sites. From the superimposed sextets of the B-site pattern result typical values of isomer shift and internal magnetic field strength due to different environments of the B-site iron. It is shown that V ions both enhance the conduction electron density at the neighbouring Fe ions and diminish the strength of the magnetic interactions.     

In-Process Particle Size Distribution Measurements and Control

In-process measurement of particle size and concentration distributions provides continuous analysis and quality control of a product stream. Elimination of sample handling and operator manipulation is now possible for most pneumatic flows using optical methods which are properly interfaced with the process stream. The EPCS (Ensemble Particle Concentration & Size) described in the following has been used to obtain detailed size distribution measurements in powder production facilities at two second intervals, and has been successfully used for automatic feedback control.     

光子相关光谱的自寻优累积反演算法实现

提出自寻优方案改进,用于光子相关光谱技术测量纳米颗粒粒径及分布的累积反演算法.阐述光子相关光谱技术测量纳米颗粒的基本原理.详细分析光子相关光谱技术中传统累积反演算法的原理,分析传统方法中造成反演结果不稳定的主要原因.提出以标准差为判定依据的自寻优累积反演算法,改善累积反演算法的测量精度和稳定性.实验结果证明方法可行可靠.     

Comparative Test of Methods to Determine Particle Size and Particle Size Distribution in the Submicron Range

Among the most important characteristic properties of disperse systems such as latices, pigments, ceramic materials or drug formulations are the particle size and the particle size distribution. To measure these quantities, several methods and measuring instruments based on different physical principles are available. These include turbidimetry, dynamic and static light scattering, electron microscopy with image analysis, ultra- and disc centrifugation, light diffraction and the electrical sensing zone method. All these measuring techniques are doubtless necessary because of the large product variety and the broad particle size range. However, some problems arise if different techniques are used and the results are compared uncritically without considering to the application range and the resolution of the methods. An extensive comparative test was therefore carried out using seven latices in the submicron range with defined monomodal, bimodal and hexamodal particle size distributions. The most important methods of determining average particle size values and particle size distributions were tested and compared. Of the methods to determine only average particle sizes, turbidimetry is the most efficient, followed by dynamic light scattering with cumulants evaluation. Static light scattering only yields accurate results for small particles with narrow particle size distributions. Of the methods to determine particle size distributions, ultracentrifugation and, somewhat less, disc centrifugation and electron microscopy with image analysis are the most efficient. Dynamic light scattering only yields reliable results in the case of small particles with narrow distribution curves. Light diffraction and the electrical sensing zone method are less suitable for the submicron range.     

Shape-induced anisotropy in epitaxial Fe3O4 nanopillars

Fe₃O₄ nanopillars with remarkably high uniformity and crystallinity are grown on (100)-oriented magnesium aluminate substrates by pulsed laser deposition with a simple anodic-aluminum-oxide template method. Compared with Fe₃O₄ full film, the nanopillars exhibit higher in-plane magnetic saturation field and lower out-of-plane saturation field. The angular-dependent ferromagnetic resonance, investigated by electron spin resonance spectroscopy, confirms the shape-induced anisotropy change in Fe₃O₄ nanopillars. High Gilbert damping parameter of 0.23 is obtained by measuring the resonance field at different microwave frequencies.     

Angular Distribution of Hyperfine Magnetic Field in Fe3O4 and Fe66Ni34 from Mössbauer Polarimetry

Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (K–Rb)₂SnCl₆ and K₂(Sn–Re)Cl₆ and the nonisomorphic system K₂SnCl₆:Al³⁺ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.     

Charge and orbital order in Fe3O4

Charge and orbital ordering in the low-temperature monoclinic structure of magnetite (Fe3O4) is investigated using the local spin density approximation with Coulomb interaction correction method. While the difference between t(2g) minority occupancies of Fe(2+)(B) and Fe(3+)(B) cations is large and gives direct evidence for charge ordering, the screening is so effective that the total 3d charge disproportion is rather small. The charge order has a pronounced [001] modulation, which is incompatible with the Anderson criterion. The orbital order agrees with the Kugel-Khomskii theory.     

Preparation of Fe3O4/polystyrene composite particles from monolayer oleic acid modified Fe3O4 nanoparticles via miniemulsion polymerization

Fe₃O₄/polystyrene composite particles were prepared from oleic acid (OA) modified Fe₃O₄ nanoparticles via miniemulsion polymerization. It was concluded that the surface properties of OA modified magnetite nanoparticles have a great effect on preparation of the composite particles. When Fe₃O₄ nanoparticles coated by multilayer of OA was employed, there were large amounts of free polystyrene particles in the product. Fe₃O₄/polystyrene composite particles with defined structure and different magnetite content can be readily prepared from monolayer OA modified Fe₃O₄ nanoparticles. It was concluded that surface of the monolayer OA modified Fe₃O₄ nanoparticles is more hydrophobic than that of the multilayer coated ones, thus improving the dispersibility of the Fe₃O₄ nanoparticles in styrene monomer and allowing preparation of the Fe₃O₄/polystyrene composite particles with defined structure and controllable magnetite content.     

Deposition of ZnO Nanocrystals on Fe3O4 Nanocubes and Their Special Luminescent and Magnetic Properties

With increasing miniaturization, it is extremely important to maintain the magnetization stability at small scale. Herein, more efforts and interests focus on the interface of magnetic core and semiconductor shell to obtain desired magnetic and/or luminescent properties. Here, Fe₃O₄ nanocubes are synthesized via a thermal decomposition followed by coating ZnO nanocrystals. To create a large interface, large Fe₃O₄ nanocubes with 78 ± 3 nm average side‐length are synthesized through adjusting the ratio of iron precursor to stabilizer. The average diameter of the particular ZnO nanostructures coated on the nanocubic Fe₃O₄ is around 10 ± 2 nm. In addition to the photoluminescent properties of the ZnO‐coated nanostructures, core‐shell Fe₃O₄@ZnO nanostructures demonstrate enhanced UV absorption at 360 nm, which has a 20 nm blueshift compared to bulk ZnO. The superparamagnetic properties of Fe₃O₄@ZnO core–shell hybrid nanocrystals at room temperature are dominated by the ferromagnetic properties when the temperature is lower than the Blocking temperature, 235.7 K. The observed exchange bias and temperature‐dependent magnetization can result from the interfacial interphase between ZnO and Fe₃O₄. The anisotropy contributed by the interfacial interphase allows the nanostructures to maintain stable magnetization in miniaturized devices.     

Spin and orbital magnetic moments of Fe3O4

We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.     

Particle Size Distribution and Aspect Ratio of Organic Pigments

Particle size and aspect ratio are amongst the most important parameters which determine the application properties of pigments, fillers and powders for ceramics. A statistical characterization of the samples is therefore needed. In this paper we discuss the measurement of bivariate size distributions of organic pigments and describe a correction procedure for particles with interchanged crystallographic axes. During the crystallization of a pigment, the larger aspect ratios usually result from faster growth rates.     

不同粒径街道灰尘中Zn的分布特征

在宿州市城区采集23个街尘样品,利用X射线荧光光谱法(XRF)测定了4个粒径区间(250-500、150-250、75-150μm和＜75μm)街尘中的Zn含量,并利用单因子指数法评价了宿州市街尘Zn污染状况.结果发现:宿州市街尘Zn含量在各粒径区间存在明显差异,其中以＜75μm和75-150μm粒径段的含量最高,说明...