Magnetic properties of ZnO-doped cobalt ferrite

The cobalt ferrites with chemical composition Co1+xZnxFe2-2xO4 (r=0.0, 0.1, 0.2, 0.4) were obtained with conventional solid reaction. The ZnO-doped samples have lower lattice constant than CoFe2O4 by adjusting Co ions to the octahedral sites. The results show that doping ZnO could extremely improve the magnetic properties. In comparison with pure CoFe2O4, the little ZnO-doped sample has higher permeability and much lower coercivity at the condition of a little decrease of magnetization saturation. Sample with x=0.1 shows evident magnetostrictive effect at the magnetic field of 30-60 mT while pure cobalt ferrite sample does not, though the saturation magnetostriction decreases. These indicate that ZnO-doping improves the magnetostrictive sensitivity of the cobalt ferrites and have potential applications in magnetoelectric devices and magnetic detector.

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Through floating catalyst chemical vapour deposition(CVD) method, well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO2/Si surface under ac electric fields at relatively low temperature(280 degrees C). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace. The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at similar to 590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products. (C) 2007 Elsevier B.V. All rights reserved.

High-frequency ferromagnetic resonance on ultrafine cobalt particles

We report on high-frequency (300-700 GHz) ferromagnetic resonance (HF-FMR) measurements on cobalt superparamagnetic particles with strong uniaxial effective anisotropy. We derive the dynamical susceptibility of the system on the basis of an independent-grain model by using a rectangular approach. Numerical simulations give typical line shapes depending on the anisotropy, the gyromagnetic ratio, and the damping constant. HF-FMR experiments have been performed on two systems of ultrafine cobalt particles of different sizes with a mean number of atoms per particles of 150 +/- 20 and 310 +/- 20. In both systems, the magnetic anisotropy is found to be enhanced compared to the bulk value, and increases as the particle size decreases, in accordance with previous determinations from magnetization measurements. Although no size effect has been observed on the gyromagnetic ratio, the transverse relaxation time is two orders of magnitude smaller than the bulk value indicating strong damping effects, possibly originating from surface spin disorders.

Magnetic properties of ZnO-doped cobalt ferrite

The cobalt ferrites with chemical composition Co1+xZnxFe2-2xO4 (r=0.0, 0.1, 0.2, 0.4) were obtained with conventional solid reaction. The ZnO-doped samples have lower lattice constant than CoFe2O4 by adjusting Co ions to the octahedral sites. The results show that doping ZnO could extremely improve the magnetic properties. In comparison with pure CoFe2O4, the little ZnO-doped sample has higher permeability and much lower coercivity at the condition of a little decrease of magnetization saturation. Sample with x=0.1 shows evident magnetostrictive effect at the magnetic field of 30-60 mT while pure cobalt ferrite sample does not, though the saturation magnetostriction decreases. These indicate that ZnO-doping improves the magnetostrictive sensitivity of the cobalt ferrites and have potential applications in magnetoelectric devices and magnetic detector.

Corrosion inhibition of carbon steel in tetra-n-butylammonium bromide aqueous solution by benzotriazole and Na3PO4

The corrosion inhibition behavior of benzotriazole, Na3PO4 and their mixture on carbon steel in 20 wt.% (0.628 mol l(-1)) tetra-n-butylammonium bromide aerated aqueous solution was investigated by weight-loss test, potentiodynamic polarization measurement, electrochemical impedance spectroscopy and scanning electron microscope/energy dispersive X-ray techniques. The inhibition action of BTA or SP or inhibitors mixture on the corrosion of carbon steel is mainly due to the inhibition of anodic process of corrosion. The results revealed that inhibitors mixtures have shown synergistic effects at lower concentration of inhibitors. At 2 g l(-1) BTA and 2 g l(-1) SP showed optimum enhanced inhibition compared with their individual effects.

MoNi/gamma-Al2O3 Catalyst: Preparation and Catalytic Activity for Acetic Acid Hydrotreating

MoNi/gamma-Al2O3 catalysts were prepared by the impregnation method. The catalyst samples were characterized by XRD and TPR. The effects of Mo promoter content and the catalyst reducing temperature Oil hydrotreatment activity of the catalyst were studied under 200 degrees C and 3 MPa hydrogen pressure using acetic acid as the model compound. The XRD results indicate that the addition of Mo promoter is beneficial to the uniformity of nickel species on the catalyst and decreases the Interaction between nickel species and the support Which results in the decrease the of NiAl2O4 spinel formation. The addition of Mo promoter also decreases the reducing temperature of the catalyst. After the catalyst of 0.06 MoNi/gamma-Al2O3 being reduced Under the atmosphere of H-2/N-2(5/95, V/V), nickel oxide was reduced to Ni-0. The reaction was promoted obviously upon the addition of the MoNi/gamma-Al2O3 catalyst reduced at 600 degrees C. The Mo-modified Ni/gamma-Al2O3 catalyst reduced at 600 degrees C displayed the highest activity during the reaction, the conversion of acetic acid reached the highest point of 33.2%. The products included ethyl acetate and water.

Partial oxidation reforming of biomass fuel gas over nickel-based monolithic catalyst with naphthalene as model compound

With naphthalene as biomass tar model compound, partial oxidation reforming (with addition of O-2) and dry reforming of biomass fuel gas were investigated over nickel-based monoliths at the same conditions. The results showed that both processes had excellent performance in upgrading biomass raw fuel gas. Above 99% of naphthalene was converted into synthesis gases (H-2+CO). About 2.8 wt% of coke deposition was detected on the catalyst surface for dry reforming process at 750 degrees C during 108 h lifetime test. However, no Coke deposition was detected for partial oxidation reforming process, which indicated that addition of O-2 can effectively prohibit the coke formation. O-2 Can also increase the CH4 conversion and H-2/CO ratio of the producer gas. The average conversion of CH4 in dry and partial oxidation reforming process was 92% and 95%, respectively. The average H-2/CO ratio increased from 0.95 to 1.1 with the addition of O-2, which was suitable to be used as synthesis gas for dimethyl ether (DME) synthesis.

Production of biodiesel from soapstock using an ion-exchange resin catalyst

The feasibility of biodiesel production from soapstock containing high water content and fatty matters by a solid acid catalyst was investigated. Soapstock was converted to high-acid acid oil (HAAO) by the hydrolysis by KOH and the acidulation by sulfuric acid. The acid value of soapstock-HAAO increased to 199.1 mg KOH/g but a large amount of potassium sulfate was produced. To resolve the formation of potassium sulfate, acid oil was extracted from soapstock and was converted to HAAO by using sodium dodecyl benzene sulfonate (SDBS). The maximum acid value of acid oil-HAAO was 194.2 mg KOH/g when the mass ratio of acid oil, sulfuric acid, and water was 10:4:10 at 2% of SDBS. In the esterification of HAAO using Amberylst-15, fatty acid methyl ester (FAME) concentration was 91.7 and 81.3% for soapstock and acid oil, respectively. After the distillation, FAME concentration became 98.1% and 96.7% for soapstock and acid oil. The distillation process decreased the total glycerin and the acid value of FAME produced a little.

Clathrate Dissociation Conditions for Methane + Tetra-n-butyl Ammonium Bromide (TBAB) + Water

Hydrate equilibrium data of the CH4 + tetra-n-butyl ammonium bromide (TBAB) + water have been measured by using the isothermal pressure search method for four components of TBAB aqueous solutions. The three-phase equilibrium lines obtained in the present study are shifted to the low-temperature or high-pressure side from that of the stoichiometric TBAB solution. Moreover, methane uptake into semi-clathrates is confirmed by a shift in the clathrate regions when methane is present. The experiments are carried out in the pressure range of (0.5 to 11) MPa and in the temperature range of (281.15 to 295.15) K.