Magnetic characterization of Co1-xNixFe2O4 (0 <= x <= 1) nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of Ni-doped cobalt ferrite [Co1-xNixFe2O4(0 <= x <= 1)] synthesized by coprecipitation route have been studied as a function of doping concentration (x) and particle size. The size of the particles as determined by X-ray diffractometer (XRD) and transmission electron microscope (TEM) analyses was found in the range 12-48 nm. The coercivity (H-C) and saturation magnetization (M-S) showed a decreasing behavior with increasing Ni concentration. M-S of all the samples annealed at 600 degrees C lies in the range 65.8-13.7 emu/gm. Field-cooled (FC) studies of the samples showed horizontal shift (exchange bias) and vertical shift in the magnetization loop. Strong decrease in exchange bias (H-b) and vertical shift (delta M) was found for low Ni concentrations while negligible decrease was found at higher concentrations. The presence of exchange bias in the low Ni-concentration region has been explained with reference to the interface spins interaction between a surface region (with structural and spin disorder) and a ferrimagnetic core region. M(T) graphs of the samples showed a decreasing trend of blocking temperature (T-b) with increasing Ni concentration. The decrease of T-b with increasing Ni concentration has been attributed to the lower anisotropy energy of Ni+2 ions as compared to Co+2 that increases the probability of the jump across the anisotropy barrier which in turn decreases the blocking temperature of the system.

Preparation of Microporous Membranes by Swift Heavy Ion Irradiation and Impedance Characterization

Polypropylene (PP) microporous membranes were successfully prepared by swift heavy ion irradiation and track-etching. Polypropylene foils were irradiated with Au-197 ions of kinetic energy 11.4 MeV.u(-1) (total energy of 2245.8 MeV) and fluence 1x10(8) ions.cm(-2) at normal incidence. The damaged regions produced by the gold ions along the trajectories were etched in H2SO4 and K2Cr2O7 solutions leading to the formation of cylindrical pores in the membranes. The pore diameters of the PP microporous membranes increased from 380 to 1610 nm as the etching time increased from 5 to 30 min. The surface and cross-section morphologies of the porous membranes were characterized by scanning electron microscopy (SEM). The micropores in the membranes were found to be cylindrical in shape, homogeneous in distribution, and equal in size. Some mathematical relations of the porosity of the PP microporous membranes were established by analytic derivation. The microporous membranes were used in lithium-ion batteries to measure their properties as separators. The electrical conductivity of the porous membrane immersed in liquid electrolyte was found to be comparable to that of commercial separators by electrochemical impedance spectroscopy (EIS). The results showed that the porosity and electrical conductivity were dependent on the ion fluence and etching time. By adjusting these two factors, microporous membranes with good porosity and electrical conductivity were made that met the requirements for commercial use.

Synthesis and characterization of carbon black supported Pt-Ru alloy as a model catalyst for fuel cells

A set of bimetallic Pt-Ru catalysts prepared by co-impregnation of carbon black with ruthenium(III) chloride hydrate and hydrogen hexachloroplatinate(IV) hydrate were investigated by temperature-programmed reduction (TPR), chemisorption of hydrogen, transmission electron microscopy (TEM), microcalorimetry of adsorbed CO and a structure-sensitive reaction (n-hexane conversion). The results showed that the volumetric capacities for CO and H-2 adsorption is influenced in the bimetallic Pt-Ru catalysts by the formation of a Pt-Ru alloy. The n-hexane reaction revealed that the reaction mechanism for the pure Pt catalyst mainly occurs via cyclic isomerization and aromatization due to the presence of bigger Pt surface ensembles, whereas the Pt-Ru catalysts exhibited predominantly bond-shift isomerization by the diluting effect of Ru metal addition. The differential heats of CO chemisorption on Pt-Ru catalysts fell between the two monometallic Pt and Ru catalysts extremes. (C) 2004 Elsevier B.V. All rights reserved.

High-throughput characterization of heterogeneous catalysts by temperature-programmed analysis method

A multistream reactor for high-throughput examining the surface acidity by NH3-TPD method by application of multistream mass spectrometer screening (MSMSS) technique has been developed. This method allows for examining the surface acidity of 10 catalyst samples in about 6 h, which is an improvement over the traditional process. The demonstration of the feasibility of high-throughput TPD can be significant in convincing the hardened traditionalists in the heterogeneous catalysis community that, combinatorial methods indeed should have an important place in scientific catalyst research and development. The developed method could also be used for almost all the temperature-programmed analysis theoretically with careful designed multistream reactors. (C) 2003 Elsevier B.V. All rights reserved.

Preparation and characterization of monolithic columns for capillary electrochromatography with weak electroosmotic flow

Monolithic columns of capillary electrochromatography (CEC) with weak electroosmotic flow (EOF) have been prepared by in situ polymerization of butyl methacrylate and ethylene dimethacrylate, without any charged groups in the reaction mixture. The reproducibility of such columns has been proved good no matter whether they are prepared in the same batch or in different batches. In the case of BMA-EDMA monoliths, besides the traditional ternary mixture - 1-propanol, 1,4-butanediol, and water, binary porogenic solvents with only alcohols have also been adopted. Compared with ternary porogenic solvents, the design with binary ones allows for fine control of the pore diameter and the formation of the specific surface of the monolithic polymers. The composition of porogenic reagents has also been shown to have an effect on EOF in the column systems. In addition, the Joule heat effect in such columns has been studied by varying the inner diameter of columns. Through the separation of acidic compounds, monolithic columns with low EOF have shown potential in the analysis of charged samples.

Preparation and characterization of multiwalled carbon nanotube-supported platinum for cathode catalysts of direct methanol fuel cells

Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2-5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.

Boundary Characterization Experiment Series Overview

Ocean acoustic propagation and reverberation in continental shelf regions is often controlled by the seabed and sea surface boundaries. A series of three multi-national and multi-disciplinary experiments was conducted between 2000-2002 to identify and measure key ocean boundary characteristics. The frequency range of interest was nominally 500-5000 Hz with the main focus on the seabed, which is generally considered as the boundary of greatest importance and least understood. Two of the experiments were conducted in the Mediterranean in the Strait of Sicily and one experiment in the North Atlantic with sites on the outer New Jersey Shelf (STRATAFORM area) and on the Scotian Shelf. Measurements included seabed reflection, seabed, surface, and biologic scattering, propagation, reverberation, and ambient noise along with supporting oceanographic, geologic, and geophysical data. This paper is primarily intended to provide an overview of the experiments and the strategies that linked the various measurements together, with detailed experiment results contained in various papers in this volume and other sources

Solvothermal synthesis and characterization of Ln (Eu3+, Tb3+) doped hydroxyapatite

Luminescent Ln (Eu3+, Tb3+) doped hydroxyapatite (Eu:HAp, Tb:HAp) phosphors were successfully fabricated via the cetyltrimethylammonium bromide (CTAB)/n-octane/n-butanol/water microemulsion-mediated solvothermal process. The structure, morphology, and optical properties were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectra as well as the kinetic decays, respectively.

Fabrication and characterization of CdTe nanoparticles attached to poly(4-vinylpyridine) nanofibers

The major objective of this work was to characterize the status of CdTe nanoparticles attached to the surface of poly(4-vinylpyridine) (P4VP) nanofibers. Scanning electron microscopy and transmission electron microscopy images indicated that the attachment of CdTe nanoparticles enlarged the diameter of P4VP nanofibers. Moreover, the results of the energy-dispersive X-ray spectrum and the electron diffraction pattern revealed that the deposition on the surface of P4VP nanofibers was CdTe in a cubic lattice

Nanoparticle-amplified Surface Plasmon Resonance Study of Protein Conformational Change at Interface

This paper reports the study of protein conformational change by Au nanoparticles (AUNPs)-amplified surface plasmon resonance (SPR) spectroscopy. Taking cytochrome c (Cyt c) as an example, this paper gives a detailed description of the construction of metal-protein-metal sandwich nanostructure consisting of an Au film underlayer, a cytochrome c intermediate layer and an AuNPs upper layer. The incorporation of AuNPs into SPR biosensing results in increased SPR sensitivity to protein conformational change as demonstrated by acid denaturation of Cyt c. It suggests the conformational change of surface-confined Cyt c leads to the distance and electromagnetic coupling variations of Au film-AuNPs.

Ultrathin platinum-group metal coated hierarchical flowerlike gold microstructure: Electrochemical design and characterization

The deliberate tailoring of hierarchical flowerlike gold microstructure (HFGMs) at the ultrathin level is an ongoing challenge and could introduce opportunities for new fabrication and application in many fields. In this paper. a templateless, surfactantless, electrochemical strategy for fabrication of ultrathin platinum-group metal coated HFGMs is proposed. HFGMs were prepared by simple electrodeposition on an indium tin oxide (ITO) substrate.

Highly Uniform and Monodisperse Ba2CIF3 Microrods: Solvothermal Synthesis and Characterization

One-dimensional hexagonal Ba2CIF3 microrods with highly uniform morphology and size have been successfully synthesized via a facile solvothermal method at a low temperature (160 degrees C). X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the samples. The synthesis process, based on a phase-transfer and separation mechanism, allows the control of properties such as particle size and shape in low dispersity by bonding the surfactant oleic acid to the crystal surface.

Synthesis, characterization and mechanism of cetyltrimethylammonium bromide bilayer-encapsulated gold nanosheets and nanocrystals

Single-crystal Au nanosheets and fcc gold nanocrystals of uniform size were synthesized by a novel and simple route. The results of field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated the formation of the single-crystal structure of gold nanosheets and fcc nanocrystals. Energy-dispersive analysis of X-ray (EDAX) showed absorbance of cetyltrimethylammonium bromide (CTAB) molecules onto the surface of gold nanostructures.