Arsenate removal by zero valent iron: Batch and column tests

This study investigates the efficiency of zero valent iron (ZVI) to remove arsenate from water. Batch experiments were carried out to study the removal kinetics of arsenate under different pH values and in the presence of low and high concentrations of various anions (chloride, carbonate, nitrate, phosphate, sulphate and borate), manganese and dissolved organic matter. Borate and organic matter, particularly at higher concentrations, inhibited the removal of arsenic. Column tests were carried out to investigate the removal of arsenate from tap water under dynamic conditions. The concentrations of arsenic and iron as well as the pH and Eh were measured in treated water. Efficient removal of arsenate was observed resulting at concentrations below the limit of 10 μg/L in treated waters.     

Preparation and characterization of zero valent iron powders via transfer type reductor using iron oxide from the acid regeneration process

In this study, zero valent iron (ZVI) powders were generated by reducing iron oxide powders obtained from a pickling line in a transfer type reductor. The physical and chemical characteristic of the produced ZVI powders were analyzed by using instruments. Reaction activities of ZVI powders for decomposition of a methylene blue were evaluated. The mean size of ZVI powders increased and the specific surface area decreased with increasing reduction temperature due to sintering. The methylene blue decomposition rate increased with dose of ZVI powders. The ZVI powders generated by reducing iron oxide showed higher decomposition efficiencies than the commercial ZVI powders at all pH values tested in this study. Both non-commercial ZVIs showed a higher decomposition rate at a lower pH.     

Effect of an electric field on the oxidation of aluminium at room temperature

Effect of an applied electric field on the oxidation rate of vacuum deposited aluminium thin films were studied at room temperature in the laboratory atmosphere. Above the critical field, a negative potential applied to the film enhanced the rate of oxidation, while a positive field retarded the rate. This suggests an oxidation mechanism involving cationic diffusion. The observed change in the rate of oxidation for an applied field agrees with the Mott-Cabrera theory.     

Change in reaction pathway of nickel(II) complex induced by magnetic fields

Three identical hydrothermal self-assembly reactions in a mixture of nickel nitrate hexahydrate, nicotinic acid, sodium azide were carried out with the applied magnetic fields of 0, 0.15, 0.3 T, respectively. It was found that [Ni_1.5(N₃)(nic)₂(Hnic)]_n can be obtained at 160 °C for 48 h without an applied magnetic field, while the final product totally changed into [Ni₂(nic)₄(H₂O)] as a 0.3 T weak magnetic field was employed in the reaction. Both of the two products show three-dimensional frameworks, however, they display two different coordination geometries with different ligands. We consider the mechanism base on changes of magnetic susceptibilities and structures of [Ni₂(nic)₄(H₂O)], and propose a view that the magnetic field can reduce the activation energy of reaction pathways according to transition state theory. The possible reason of the decrease of activation energy is that a magnetic field can mediate coupling among the Ni²⁺ ions during the formation of [Ni₂(nic)₄(H₂O)], which is indicated by the slight changes of microstructure of crystal, such as bond angle and length.     

The influence of the magnetic field on the performance of an active magnetic regenerator (AMR)

The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20-40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5-20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30-50% but the maximum temperature span by only 20-30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry.     

磁场诱导自蔓延高温合成钡铁氧体

本文采用外加磁场诱导自蔓延高温合成钡铁氧体,试验用的电磁场强度最高可达1.3T,对无磁场和不同磁场强度下合成的铁氧体的形貌、相组成和磁性能分别进行了表征.研究结果表明:外加磁场对燃烧温度有影响,燃烧温度影响产物转换,燃烧温度较低时,产物为BaFe2O4与BaFe12O19相共存;本试验条件下,磁场强度为0.86T时,合成为M型的钡铁氧体(BaFe12O19),产物结晶完整,有六角片状的钡铁氧体,且性能达到了最佳,矫顽力达到1083(4π)-1·kA·m-1,比剩余磁化强度为16.16 A·m2/kg,比不加磁场条件下分别提高50%和提高32%,说明适当的磁场强度诱导自蔓延高温合成可以改善BaFe12O19的磁性能.     

In-situ scanning electron microscopy and electron backscatter diffraction investigation on the oxidation of pure iron

Abstract

α-iron samples, with a 4 to 6 nm oxide layer on top of the surface due to preparation, were oxidised in situ within a scanning electron microscopy equipped with electron back-scatter diffraction. At 773 and 973 K, two different growth mechanisms during the initial stage of iron oxide formation could be observed, layer-by-layer growth at 773K and island growth at 973 K. The growth mechanism at 973K is correlated to the formation of a thin layer of Fe_1–XO (wüstite) prior to Fe₃O₄ (magnetite) crystallisation whereas at 773K only magnetite was found as newly grown oxide. Magnetite showed a strong epitaxial relationship to α-iron with its {111} plane growing preferentially on the {110} plane of iron.     

Effect of magnetic field on natural convection in a vertical cylindrical annulus

Natural convection of a low Prandtl number electrically conducting fluid (Pr = 0.054) under the influence of either axial or radial magnetic field in a vertical cylindrical annulus has been numerically studied. The inner and outer cylinders are maintained at uniform temperatures and the horizontal top and bottom walls are thermally insulated. A finite difference scheme consisting of alternating direction implicit (ADI) method and successive line over relaxation (SLOR) method is used to solve the vorticity stream function formulation of the problem. Detailed numerical results of heat transfer rate, temperature and velocity fields have been presented for 1  λ  10, 0.5  A  2, 10³  Ra  10⁶ and 0  Ha_r, Ha_x  10². The computational results reveal that in shallow cavities the flow and heat transfer are suppressed more effectively by an axial magnetic field, whereas in tall cavities a radial magnetic field is more effective. It is also found that the flow oscillations can be suppressed effectively by imposing an external magnetic field. The average Nusselt number increases with radii ratio but decreases with the Hartmann number. Further, the present numerical results are shown to be in good agreement with the available benchmark solutions under the limiting conditions.     

Studies of the magnetic field intensity on the synthesis of chitosan-coated magnetite nanocomposites by co-precipitation method

Chitosan-coated magnetite nanocomposites (Fe₃O₄/CS) were prepared under different external magnetic field by co-precipitation method. The effects of the magnetic field intensity on phase composition, morphology and magnetic properties of the Fe₃O₄/CS nanocomposites were investigated by X-ray diffractometer (XRD), Fourier transform infrared analysis (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that the intensity of the magnetic field in the co-precipitation reaction process did not result in the phase composition change of the magnetic chitosan but improved the crystallinity of magnetite. The morphology of Fe₃O₄/CS nanocomposites was greatly changed by the magnetic field. It was varied from random spherical particles to chain-like cluster structure and rod-like cluster structure with the magnetic field intensity increased in the synthetic process. The VSM results indicated that all the products had excellent superparamagnetic properties regardless of the presence or the absence of the magnetic field, and the saturation magnetization values of the Fe₃O₄/CS nanocomposites were significantly improved by the magnetic field.     

Anodic oxidation of wastewater containing the Reactive Orange 16 Dye using heavily boron-doped diamond electrodes

Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 × 10²¹ atoms cm⁻³, respectively. The boron levels were evaluated from Mott-Schottky plots also corroborated by Raman's spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (1 1 1) and (1 0 0). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.     

Effect of magnetic field on the heat and mass transfer in a vertical annulus

This paper reports the effect of axial or radial magnetic field on the double-diffusive natural convection in a vertical cylindrical annular cavity. The boundary conditions at the side walls are imposed in such a way that the thermal and solutal buoyancy effects are either cooperating or opposing, resulting in a cooperating gradients or opposing gradients flow configuration. The top and bottom walls are insulated and impermeable. The governing equations of this fluid system are solved by the Alternating Direction Implicit and the Successive Line Over Relaxation methods. Total heat and mass transfer rates across the cavity are calculated by evaluating the average Nusselt and Sherwood numbers. The main objective of the present numerical study is to understand the effect of magnetic field on the double-diffusive convection in the annular cavity. From the numerical results, it is found that the magnetic field suppresses the double-diffusive convection only for small buoyancy ratios. But, for larger buoyancy ratio, the magnetic field is effective in suppressing the thermal convective flow. Further, the magnetic field is effective when it is applied perpendicular to the main flow.     

Unique properties of polyaniline in the presence of applied magnetic field and ferric chloride

Fe-contained polyaniline (abbreviated as PANI–Fe) was prepared by chemical oxidation of aniline with ammonium peroxydisulfate oxidant in 0.5 mol dm⁻³ HCl and an adequate content of FeCl₃·6H₂O solution in the presence of an applied magnetic field at room temperature. The X-ray photoelectron spectroscopy (XPS) and UV–vis and FTIR spectra suggest that there is an interaction between FeCl₃ and PANI chains, but PANI–Fe backbone is essentially identical with that of parent polyaniline. The electron paramagnetic resonance (EPR) spectrum shows that there were unpaired electrons in PANI–Fe synthesized in the presence of an applied magnetic field, the spin density and the conductivity of which are 7.308 × 10²⁰ spins g⁻¹ and 0.891 S cm⁻¹, respectively. The plot of magnetization (M) vs. the applied magnetic field (H) displays that the PANI–Fe possesses soft ferromagnetic behavior at room temperature. The results of cyclic voltammogram show that the PANI–Fe film is of excellent electrochemical activity.     

铁粉纯度和粒径对磷化铁粉软磁复合材料磁性能的影响

研究了铁粉纯度和粒径对磷化铁粉软磁复合材料磁性能的影响。结果表明,铁粉经磷化后,表面成功包覆了完整均匀的磷酸盐绝缘层。铁粉纯度提高,软磁复合材料磁芯的密度和磁导率增大,同时磁滞损耗降低。铁粉粒度增大,磁芯密度和磁导率增加,中高频率下磁损耗明显增加,且频率越高越明显。     

Effect of external magnetic fields on shaped-charge operation

This paper deals with electromagnetic actions that allow one to control the shaped-charge effect at different stages of shaped-charge operation. A decrease in penetration of the shaped-charge jet is attained by production of an axial magnetic field in the shaped-charge liner immediately before shot, and production of a magnetic field in the conducting target material that is transverse to the direction of jet propagation. The considerable decrease in the penetration capability of the charge observed in the experiments is attributed to a sharp amplification of the magnetic field in the jet formation region upon liner collapse. The effects accompanying the “field pumping” prevent the normal formation of a shaped-charge jet. A model of magnetic field generation in a conducting medium subjected to high-velocity deformation with particle elongation along the magnetic flux lines is considered. X-ray photographs of shaped-charge jets formed from a “magnetized liner” are given. Theoretical calculations have shown that deformation conditions that can provide for intense magnetic field generation also arise during high-velocity jet penetration into a conducting target across the flux lines of the initial magnetic field previously produced in the target.     

Effect of pressure on plasma sheath in a magnetic field

The effects of collisions on plasma sheath in an external magnetic field have been investigated by considering the collisions between ions and neutral gas atoms. The ion fluid equations containing an external magnetic field and the collisions are solved numerically to study the ion dynamics under various pressures.     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

Influence of an external magnetic field on the formation of self-assembled monolayers of dodecanethiol on polycrystalline gold electrode

This paper reports the preparation of dodecanethiol self-assembled monolayers (C₁₂SH-SAMs) on polycrystalline gold electrodes in a magnetic field. The qualities of C₁₂SH-SAMs were characterized by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that highly dense and well-ordered SAMs could form in a relatively short time (3 h), indicating that the rate of SAMs formation increased under an external magnetic field compared with the natural self-assembly process. Moreover, the results of CV and EIS measurements also suggested that the presence of a magnetic field had influenced the qualities of the SAMs; the stronger magnetic intensity can help to obtain much denser and well-ordered SAMs.     

The effect of magnetic field on the shape of etch pits of paracetamol crystals

In the present study we investigate the effect of magnetic field on the shape of etch pits of the crystals of p-hydroxyacetanilide (paracetamol), which is widely used in pharmacy as antipyretic, antiphlogistic medicine. It was discovered that the magnetic field (H=0.5 T, τ=15 min) changes the morphology of etch pits and shifts dislocations in paracetamol crystal. Activation energy of the changes induced by the action of the magnetic field was determined to be 63 kJ/mol, which is comparable with the energy of hydrogen bonds in crystal lattice. Received: 29 October 2001 / Reviewed/Accepted: 3 November 2001 /     

Simulation to improve the magnetic field in the straight section of the rectangular planar DC magnetron

For the rectangular planar DC magnetron, Gaussian type erosion profile may occur in the straight section of target and lead to lower target utilization. Considering the influence of magnetic field on the trajectories of energetic electrons, the target erosion profile and deepest eroded position are analyzed, and then the approaches of magnetic field improvement are proposed. Based on this, two magnet structures with AlNiCo and SmCo are discussed, which could be improved by fitting a shunt bar. According to 2D non-self-consistent particle simulation and Yamamura/Tawara formula, the target erosion profile could be predicted. Via the simulation, the approaches of magnetic field improvement are verified. In the same order of magnetic field intensity, the horizontal component of the magnetic field with wider distribution and larger concavity is proved to make the target utilization much increased.     

A significant promotion of the iron tetra(p-methoxylphenyl) porphyrin catalysis for the aerobic oxidation of cyclohexane using boehmite

An important issue for the application of metalloporphyrins in the chemical industry is the preparation of a reusable and active supported catalyst. In this work, a new nanocatalyst material consisting of boehmite and a second-generation iron tetraphenylporphyrin with electron-donating groups (methoxyl) has been prepared and characterised using UV-Vis and FT-IR spectroscopy, X-ray powder diffraction, scanning electron microscopy and thermal analysis. The reusability of the boehmite-supported iron tetra (p-methoxylphenyl) porphyrin catalyst for the aerobic oxidation of cyclohexane was investigated. The supported catalyst material containing only 1?mg of iron tetra (p-methoxylphenyl) porphyrin per 1?g of boehmite could be recovered easily and reused effectively for at least 10 times for the oxidation of cyclohexane. The oxidative results gave, on average, 5.1% cyclohexane conversion, 91.2% selectivity (ketone?+?alcohol) and a catalyst turnover number of 7.91?×?10⁴ over several cycles using moderate reaction conditions. The special character of the catalyst material is related to the structure of the combined boehmite and iron porphyrin.