Magnetic properties of acicular Fe1-xREx (RE = Nd, Sm, Eu, Tb; x=0, 0.05, 0.10) metallic nanoparticles

Acicular monodispersed Fe1-xREx (RE= Nd, Sm,Eu,Tb;x=0, 0.05, 0.10) metallic nanoparticles (60 +/- 5 nm in length and axial ratio similar to6) obtained by reduction of alumina-coated goethite nanoparticles-containing rare earth (RE) under hydrogen flow are reported. Alumina and maghemite thin layers on particle surface were used to protect the goethite particles against sintering and oxidation, respectively. Al and RE additions were obtained by successive heterocoagulation reactions. Aluminum sulfate (10 at.% based on Fe) was dissolved in water and the pH adjusted to 12.5 with NaOH solution. Goethite particles were suspended in this solution and CO2 gas was blown into the slurry to neutralize it to a pH 8.5 or less. Particles were purified and dehydrated to effect transformation to alumina-coated hematite nanoparticles, which were re-suspended in aqueous solution in which RE sulfate (0-0.15 at.% based on Fe) has been dissolved, and the pH increased by ammonia aqueous solution addition. Resulted alumina-coated RE-doped hematite nanoparticles were reduced to metal at 450 degreesC/12 h under hydrogen flow and passivated with nitrogen-containing ethanol vapor at room temperature. Acicular monodispersed metallic nanoparticle systems were obtained and the presence of Al and RE were confirmed by induced-coupled plasma spectrometry analysis. X-ray diffraction, Mossbauer spectroscopy, and magnetization data are in agreement with the nanosized alpha-Fe core in a bcc structure, having a spinel structure, gammaFe(2)O(3), with thickness similar to1.5 run on particle surface. Main magnetic parameters showed saturation magnetization decreases and significant increasing in the coercive field with the RE composition increases. Magnetic properties of these particles, similar to40% smaller than those commercially available, suggest a decrease in the bit-size for high-density magnetic or magneto-optics recording media application. (C) 2004 Published by Elsevier B.V.

beta-ZnMoO4 microcrystals synthesized by the surfactant-assisted hydrothermal method: Growth process and photoluminescence properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of reaction time on the particle size of ZnO and ZnO : Ce obtained by a sol-gel method

In this work particles of ZnO of size range 33-56 Angstrom were prepared by a sol-gel method. The effect of reaction time on the particle size of ZnO or ZnO:Ce was investigated by transmission electron microscopy measurements, UV-vis absorption and luminescence spectroscopy. A linear increase of the mean particle size is observed as a function of reaction time. The cerium-doped particles are bigger than the pure ZnO ones obtained at the same reaction time. A shift to lower energy at the maximum of the bands is observed in all absorption, emission and excitation spectra as a function of particle growth. From the absorption spectra the optical energy gap values (Eg) for these particles were determined. In the quantum size regime, Eg was found to decrease with particle growth.

The influence of hydrogen plasma pre-treatment on the structure of BDND electrode surface applied for phenol detection

The surface properties of boron-doped nanocrystalline diamond films treated with H(2) plasma was investigated in regard to their electrochemical response for phenol oxidation. The surface of these films is relatively flat formed by crystallites with sizes of about 40 nm. X-ray photoelectron spectroscopy analyses showed that electrode surface has a high amount of C-H bonds. This behavior is in agreement with Mott-Schottky plot measurements concerning the flat band potential that presented a value as expected for hydrogenated diamond surface. This electrode presented the phenol detection limit of 0.08 mg L(-1) for low phenol concentrations from 40 to 250 mu mol L(-1).

Application of Polysaccharide Hydrogels in Adsorption and Controlled-Extended Release of Fertilizers Processes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photothermal Study of Two Different Nanofluids Containing SiO2 and TiO2 Semiconductor Nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Stable colloidal suspensions of nanostructured zirconium oxide synthesized by hydrothermal process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Superparamagnetic Ni:SiO2-C nanocomposites films synthesized by a polymeric precursor method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Shear strength evaluation of composite-composite resin associations

Objective: The aim of this study was to investigate the shear strength between distinct associations of different commercial composite resins and their fracture modes.Methods: Nine composite-composite associations (n = 90) were prepared for shear strength evaluation and separated into the following groups: Z/Z (Filtek Z250 UD + Filtek Z250 A2); Z/ D (Filtek Z250 UD + Durafill VS A2); Z/S (Filtek Z250 UD + Filtek Supreme YT); C/C (Charisma OA2 + Charisma A2); C/D (Charisma OA2 + Durafill VS A2); C/S (Charisma OA2 + Filtek Supreme YT); H/H (Herculite XRV B2D + Herculite XRV B2E); H/D (Herculite XRV B2D + Durafill VS A2); H/S (Herculite XRV B2D + Filtek Supreme YT). Shear tests were carried out using universal mechanical test equipment with a load of 200 kgf and speed of 0.5 mm/min. Ultimate shear strength data (MPa) from all tested groups were submitted to analysis of variance (one-way ANOVA) and the Tukey test. The fractured surfaces of the test samples were visually evaluated by binocular stereomicroscope at 20 times magnification. Fractures were classified as either adhesive or cohesive or mixed.Results: The highest ultimate shear strength observed for composite-composite associations was found for the groups: Z/Z, C/S, H/H, H/S, Z/S and C/C. Those associations containing the Durafill resin were weaker than the others.Conclusion: Microparticle RBC associations presented lower shear strength than hybrid and/or nanoparticle RBC associations, once the only significant difference was found when the Durafill resin was involved. (c) 2008 Elsevier Ltd. All rights reserved.

Electro-precipitation of Fe(3)O(4) nanoparticles in ethanol

The preparation of superparamagnetic magnetite (Fe(3)O(4)) nanoparticles by electro-precipitation in ethanol is proposed. Particle average size can be set from 4.4 to 9 nm with a standard deviation around 20%. Combination of wide-angle X-ray scattering (WAXS), Electron energy loss spectroscopy (EELS) and Mossbauer spectroscopy characterizations clearly identifies the particles as magnetite single-crystals (Fe(3)O(4)). (C) 2008 Elsevier B.V. All rights reserved.

Preparation and Characterization of Novel Micro- and Nanocomposite Hydrogels Containing Cellulosic Fibrils

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Synthesis and electrochemical behavior of single-crystal magnetite nanoparticles

Water-dispersed magnetite nanoparticle synthesis from iron(II) chloride in dimethyl sulfoxide (DMSO)-water solution at different DMSO-water ratios in alkaline medium was reported. TEM and XRD results suggest a single-crystal formation with mean particle size in the range 4-27 nm. Magnetic nanoparticles are formed by the oxidative hydrolysis reaction from green rust species that leads to FeOOH formation, followed by autocatalysis of the adsorbed available Fe(II) on the FeOOH surfaces. The available hydroxyl groups seem to be dependent on the DMSO-water ratio due to strong molecular interactions presented by the solvent mixture. Goethite phase on the magnetite surface was observed by XRD data only for sample synthesized in the absence of DMSO. In addition, cyclic voltammetry with carbon paste electroactive electrode (CV-CPEE) results reveal two reduction peaks near 0 and +400 mV associated with the presence of iron(III) in different chemical environments related to the surface composition of magnetite nanoparticles. The peak near +400 mV is related to a passivate thin layer surface such as goethite on the magnetite nanoparticle, assigned to the intensive hydrolysis reaction due to strong interactions between DMSO-water molecules in the initial solvent mixture that result in a hydroxyl group excess in the medium. Pure magnetite phase was only observed in the samples prepared at 30% (30W) and 80% (80W) water in DMSO in agreement with the structured molecular solvent cluster formation. The goethite phase present on the, magnetite nanoparticle surface like a thin passivate layer only was detectable using CV-CPEE, which is a very efficient, cheap, and powerful tool for surface characterization, and it is able to determine the passivate oxyhydroxide or oxide thin layer presence on the nanoparticle surface.

Utilização de polímero hidroabsorvente no meloeiro (Cucumis melon L.) sob diferentes lâminas de irrigação

This work was carried out to evaluate the use of a hydrogel polymer in melon crop under different irrigation depths, with the objective of improve water retention, and efficiency of water and nutrient utilization by plants. One trial consisted of two treatments with four replications: a treatment with irrigation depth corresponding to 75% of gross depth and 27g of the soil conditioner per plant; the control with irrigation depth equal to the gross depth and without conditioner. The following characteristics were evaluated: root length, yield and quality of melon fruits. Root growth was bigger in the plants where soil conditioner was used. Use of soil conditioner provided an increase on melon yield and number of fruits per linear meter. Mean fruit weight and total soluble solids were not influenced by soil conditioner application and irrigation depth reduction.

Synthesis and characterization of ruthenium complexes immobilized on poly(4-vinylpyridine)

The [Ru(NH3)5(H2O)]2+ and trans-[Ru(NH3)4SO2(H2O)]2+ complexes ions were immobilized on poly(4-vinylpyridine) (4-PVP) through reactions in aqueous solutions. The stability of the imobilized complexes was checked in aqueous solution in the pH 2.0-8.0 range. The number of pyridinic nitrogens in the polymer 4-PVP is 2.80±0.05 mmol/g according to nitrogen elemental analysis. Potentiometric titration experiments showed that the accessible nitrogen, in aqueous medium, was 0.94±0.02 mmol/g with a p Ka value of 7.4±0.2. In addition, ruthenium and sulfate analysis has demonstrated that about 15% of the accessible nitrogen sites are able to coordinate to the metal centers. The characterization of the immobilized complexes was made through diffuse electronic and infrared spectroscopies and differential pulse and cyclic voltammetries. © 1993 Plenum Publishing Corporation.

Spectroscopic characterization of SnO2 gels - Code: CP11

Excitation and dynamic emission spectra of Eu3+ ions were simultaneously used with FTIR and Raman spectroscopy to study the structural evolution during SnO2 sol → gel → xerogel conversion. Results make evident an increase of the surroundings symmetry for the Eu3+ ions dissolved in SnO2 matrix and a decrease of the amount of hydroxo groups (Sn-OH) during drying. These phenomena were associated to the pursuit of the condensation reaction after gelation. © 1994 Kluwer Academic Publishers.