Lu(Fe0.75Al0.25)(2) and Lu(Fe0.50Al0.50)(2) alloys have been produced by arc-melting. DC and AC magnetization, Mossbauer spectroscopy, specific heat and neutron diffraction experiments have been performed to determine their magnetic ground state. DC magnetization curves measured at low fields (H < 1 kOe) evidence two peaks, at T-SRO and T-f, and magnetic irreversibility. The peak at T-SRO vanishes and the one at T-f smears out when high fields (H > 1 kOe) are applied. The thermal variation of AC susceptibility shows that both transitions at T-SRO and T-f are frequency dependent. Neither magnetic splitting nor broadening is observed in the Mossbauer spectra of both compounds in the T-f < T < T-SRO thermal range. A magnetically split spectrum is only observed in Lu(Fe0.75Al0.25)(2) for T < T-f. The absence of long range ferromagnetic order in both alloys is confirmed by specific heat and neutron diffraction measurements. The overall interpretation points to a clustered magnetic environment due to the random positions of Fe atoms in the crystallographic cell. At T-SRO a short range ferromagnetic order takes place within the clusters, which become frustrated at T-f, when the random anisotropy of the clusters enables their freezing. (C) 2016 Elsevier B.V. All rights reserved.

Paper

We present a study on the effect of the substitution of Fe+3 by Mn+3 on the structural and magnetic properties of strontium hexaferrite, SrFe12-xMnxO19 (0 <= x <= 5), which is synthesized by assisted high-energy ball milling. A mechanism of substitution is proposed. Fe2O3, SrCO3 and Mn2O3 powders were mixed in a stoichiometric ratio, milled for 5 h and annealed at 950 degrees C for 2 h. The X-ray diffraction patterns confirm the formation of a hexaferrite structure with small amounts of Fe2O3 as a second phase for low doping levels of Mn3+ and reveal a modification of the lattice parameters as the rate of Mn3+ substitution increases. The magnetic properties demonstrate an important reduction of the magnetic saturation and a significant increase in the coercivity field with cation substitution. The M+ ossbauer results confirm that the Mn3+ ions preferentially occupy the 2a and 12k sites while avoiding the 2b site. (C) 2016 Elsevier B.V. All rights reserved.

Paper

Nominal granular iron oxide-aluminum thin films have been prepared by simultaneous deposition of iron oxide nanoparticles, grown by the gas-phase aggregation technique, and an aluminium matrix, grown by conventional magnetron sputtering. Composition, structure and magnetic behavior have been analyzed by different techniques including TEM and AFM microscopies, EDX, RBS, X-ray absorption and Mossbauer spectroscopies and SQUID magnetometry. Both, structure and magnetic behavior, are found to be highly dependent on the preparation conditions. In particular, our work shows that for low matrix/nanoparticle ratios the aluminum is able to partially displace the iron oxide and forma core-shell iron metal-iron oxide structure. For higher ratios, on the other hand, the oxygen atoms become very diluted and their role negligible. In this case a core-shell structure consisting of an iron metal core and an iron-aluminum alloy shell is formed. Magnetization measurements indicate that in the first case the core and the shell are magnetically coupled while in the second case the two phases are magnetically uncoupled, the Fe-Al alloy presenting strong coercivity. (C) 2016 Elsevier Ltd. All rights reserved.

Paper

Nickel ferrite nanoparticles (NiFe2O4) were synthesized by electrochemical method and used as catalyst for direct oxidation of glucose, NADH and methanol. Characterization of these nanoparticles was carried out by X-ray diffraction, Mossbauer spectroscopy, and colloidal properties such as hydrodynamic radius and Zeta potential. To evaluate the catalytic properties of these nanoparticles against the oxidation process, paste graphite electrodes mixing nickel ferrites and different conductive materials (graphite, carbon nanotubes) and binders agents (mineral oil, 1-octylpyridinium hexafluorophosphate (nOPPF6)) were used. The results prove good catalytic properties of these materials, with an oxidation potential around 0.75, 0.5 and 0.8 V for glucose, NADH, and methanol, respectively. (C) 2013 Elsevier B. V. All rights reserved.

Paper

Using the electrochemical route, cobalt ferrite nanoparticles (NPs) with two different sizes were synthesized and stabilized in water by coating with citric acid. The specific absorption rate (SAR) values of aqueous suspensions of magnetic nanoparticles with crystal sizes of 13 and 28 nm were investigated in the frequency range 32-101 kHz and up to 51 mT. SAR values were higher for the larger NPs and reached 133 W/g. Numerical simulations are used for a quantitative analysis of hyperthermia experiments and seem to indicate that the larger NPs are multidomain. Cytotoxicity analysis was also performed in HeLa tumor cells; a null cytotoxicity of these nanoparticles in cell tissues were obtained.

Paper

Partially oxidized iron nanoclusters have been prepared by the gas-phase aggregation technique with typical sizes of 2-3 nm. This preparation technique has been reported to obtain clusters with interesting magnetic properties such as very large exchange bias. In this paper, a sample composition study carried out by Mossbauer and X-ray absorption spectroscopies is reported. The information reached by these techniques, which is based on the iron short range order, results to be an ideal way to have a characterization of the whole sample since the obtained data are an average over a very large amount of the clusters. In addition, our results indicate the presence of ferrihydrite, which is a compound typically ignored when studying this type of systems.

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This article describes a novel synthetic route to obtain hybrid nanostructures that combine the plasmonic properties of gold nanorods with the magnetic properties of iron oxide nanoparticles in a robust silica nanostructure. The silica matrix enhances the physico-chemical stability of the nanostructure and preserves its magneto-plasmonic properties by avoiding the interface between gold and iron oxide. In addition, the magneto-plasmonic features of the nanohybrids can be tuned due to the independent synthesis of each component. The magnetic and plasmonic properties of these nanostructures can potentially enhance the photoacoustic detection of circulating tumor cells.

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The present work seeks to enlarge the FePt nanocrystal size by submitting Colloidal Nanoparticle Clusters (CNCs) coated by a FeOx shell (FePt@FeOx) to a thermal treatment. The nanostructures were prepared by thermal decomposition in organic media under limited surfactant protection. By adjusting the molar ratio of surfactants it is possible to control the degree of oxidation and aggregation of the CNCs. The FeOx coating of the FePt CNCs resulted to be crucial during the thermal treatment to achieve a controlled crystal growth and induce a structural transition to tetragonal L1(0) FePt phase producing 31 nm nanocrystals with high magnetization and coercivity. Clustering and controlled oxidation is proposed here as a new method to overcome size limitation in the synthesis of FePt nanoparticles. (C) 2016 Elsevier Ltd. All rights reserved.

Paper

Fenites of iron, cobalt, and nickel were used as a non-enzymatic sensor for detection of hydrogen peroxide. Xray diffraction (XRD) and transmission electron microscopy revealed that the nanoparticles obtained by electrochemical route and varying the parameters synthesis show similar size of around 20 nm and a relation metal/iron equal to 1/2. The effect of pH, temperature, amount of nanoparticles, and potential has been studied to obtain the best sensor properties in terms of sensitivity and linear response. The mechanism has, CO2, been attributed to the oxidation of Fezand Nit' in the octahedral position of the spinel that enhances the catalytic reduction of hydrogen peroxide. The best sensor has been obtained with magnetite (iron fenite) with a detection limit of 7.3 x 10(6) M and a sensitivity of 4.0 x 10(-4) mu A/M. The magnetite was also applied to determine hydrogen peroxide in commercial contact lens cleaner Novoxy with satisfactory results.

Paper

Nominal granular iron oxide-aluminum thin films have been prepared by simultaneous deposition of iron oxide nanoparticles, grown by the gas-phase aggregation technique, and an aluminium matrix, grown by conventional magnetron sputtering. Composition, structure and magnetic behavior have been analyzed by different techniques including TEM and AFM microscopies, EDX, RBS, X-ray absorption and Mossbauer spectroscopies and SQUID magnetometry. Both, structure and magnetic behavior, are found to be highly dependent on the preparation conditions. In particular, our work shows that for low matrix/nanoparticle ratios the aluminum is able to partially displace the iron oxide and forma core-shell iron metal-iron oxide structure. For higher ratios, on the other hand, the oxygen atoms become very diluted and their role negligible. In this case a core-shell structure consisting of an iron metal core and an iron-aluminum alloy shell is formed. Magnetization measurements indicate that in the first case the core and the shell are magnetically coupled while in the second case the two phases are magnetically uncoupled, the Fe-Al alloy presenting strong coercivity. (C) 2016 Elsevier Ltd. All rights reserved.

Paper

A combined electrochemical/chemicalmethodwas developed in order to synthesize manganese ferrite nanoparticles. The synthesis was carried out in an electrochemical cell containing iron as anode and cathode electrodes and an electrolyte solution of manganese chloride and tetrabutyl ammonium bromide. A usual XRD, STEM compositional mapping images and ICP analysis showed the formation of spinel structure and the presence of Mn, Fe and O in the nanoparticles (NPs) with a stoichiometry Mn0.5Fe2.5O4. The nanoparticle size, shape, and morphology were characterized using electron microscopy and X-Ray absorption spectroscopy, and SQUID measurements were carried out to determine the magnetic behavior. This sample was compared with a same composition manganese ferrite obtained by electrochemical synthesis. (C) 2016 Elsevier Ltd. All rights reserved.

Paper

A series of zinc ferrite nanoparticles were synthesized following a single-step electrochemical method in aqueous medium. This strategy allowed the control of both the size and chemical composition of the nanoparticles in an easy and reproducible manner by simply varying the intensity of the applied current. The obtained nanoparticles were morphologically and structurally characterized as a function of the particle size and the Zn content in the sample by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and Raman microscopy. The formation of ZnxFe(3-x)O4 (x = 0.18-0.93) ferrite nanoparticles with crystal sizes in the range of 9 to 18 nm and with a homogeneous distribution of the Zn2+ cation in the crystalline structure was observed. However, following a thermal treatment, a migration of zinc cations was detected that led to the formation of two different crystalline phases, stoichiometric zinc ferrite and hematite. Raman microscopy revealed the formation of segregated micro-domains enriched within these crystalline phases. The study of the magnetic properties of the electro-synthesized ferrite nanoparticles with a homogeneous incorporation of Zn in the structure shows that the saturation magnetization and the coercively values are highly dependent on the chemical composition and crystal size.

Paper

Magnetic, chemical and structural properties of electrosynthesized CoxNi100 - x have been studied. The electrodeposition has been conducted both in the presence and absence of a low magnetic field. The application of a perpendicular magnetic field during the synthesis modified slightly the morphology of the alloys. These changes depend more on the film composition than on the applied field, as demonstrated by AFM images. In the absence of magnetic field, the CoxNi100 - x film grows along the (200) direction. However, when the magnetic field was applied, a preferential orientation along the (111) direction was observed. No important magnetic changes are induced by the presence of the magnetic field during the growth. Based on X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) experiments, the chemical composition of the films was preserved during preparation regardless of whether or not magnetic field is applied. There has been observed an increase in deposition rate in the presence of field even at these low magnetic fields. (C) 2015 Elsevier Inc. All rights reserved.

Paper

The electrochemical mechanism of the formation of magnetite nanoparticles is studied. The proposed mechanism suggests the formation of iron hydroxide Fe(OH)(2) in the presence of oxygen which produces lepidocrocite (gamma-FeOOH) followed by its chemical dehydration. This is in contrast to other reported mechanisms that suggest the reduction of Fe(OH)(3) at the cathode. Video frames captured during the electrosynthesis of magnetite, in a typical two-electrode cell, indicate that the nanoparticles form in the region close to the anode. The pH value near the anode and cathode changes with time, indicating the formation of nanoparticles. Additional experiments in a two-compartment cell fitted with a cationic membrane, to avoid direct intermixing of Fe2+ and OH-and possible oxide or oxyhydroxide reduction at the cathode, support this mechanism. The amount of dissolved oxygen in the electrolyte was found to be a key factor to produce magnetite by promoting the transformation of Fe(OH)(2) into (gamma-FeOOH). Hydrogen bubbling during electrosynthesis does not contribute to the reduction of the oxyhydroxides, according to X-ray diffraction results. The paper presents a proposed mechanism for the formation of magnetite, based on previous and new evidence. (C) 2017 The Electrochemical Society. All rights reserved.

Paper

Nickel ferrite nanoparticles (NiFe2O4) were synthesized by electrochemical method and used as catalyst for direct oxidation of glucose, NADH and methanol. Characterization of these nanoparticles was carried out by X-ray diffraction, Mossbauer spectroscopy, and colloidal properties such as hydrodynamic radius and Zeta potential. To evaluate the catalytic properties of these nanoparticles against the oxidation process, paste graphite electrodes mixing nickel ferrites and different conductive materials (graphite, carbon nanotubes) and binders agents (mineral oil, 1-octylpyridinium hexafluorophosphate (nOPPF6)) were used. The results prove good catalytic properties of these materials, with an oxidation potential around 0.75, 0.5 and 0.8 V for glucose, NADH, and methanol, respectively. (C) 2013 Elsevier B. V. All rights reserved.

Paper

A glycomonomer was synthesized from poly(ethylene glycol) methacrylate (PEGMA). The terminal hydroxyl moieties were activated with ester groups and subsequently the glucosamine was incorporated forming urethane linkages. The obtained glycomonomer was copolymerized with methyl acrylate by free radical polymerization varying the initial feed composition to produce different amphiphilic glycopolymers. The glycopolymers were then characterized and compared with the homologous glycopolymers based on 2-{[(D-glucosamin-2-N-yl)carbonyl]oxy}ethyl methacrylate. Both series of glycopolymers were used in emulsion polymerization of methyl acrylate as stabilizers without the addition of any cosurfactant. Although high conversions were not achieved with any of the employed surfactant, the glycopolymers provide good colloidal stability, spherical, monodisperse and small latex particles in comparison with the surfactant-free emulsion polymerization. The latex particles stabilized with the glycosurfactant based on PEGMA, containing a flexible spacer between the backbone and the glucosamine, lead to smooth films whereas the short side chain surfactant from 2-hydroxyethyl methacrylate (HEMA), with higher glass transition temperature, restricts the coalescence of particles and, therefore, the film formation. Moreover, the surface bioactivity of these polymer coatings was examined by analyzing their specific interaction with the lectin, Concanavalin A, Canavalia ensiformis. The specific and successful binding to the Concanavalin A was demonstrated by fluorescence microscopy for both series being more intense with increasing amount of glycounits in the glycopolymer stabilizers. Interestingly, the incorporation of a flexible spacer in the glycopolymer structures enhances the binding activity. (C) 2013 Elsevier Inc. All rights reserved.

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Paper

In this work, an electrochemical modified microcell is proposed to obtain local mass transfer coefficients at microscopic electrode areas. Microcell modification includes the use of a small diameter plastic injector (inner radius <200 mu m) placed inside a commercial plastic micropipette tip in a typical microcell arrangement. The flexible plastic micropipette tip facilitates the seal with the working electrode surface, without using a silicon gasket. The outflow emerging from the plastic injector impinges on the electrode surface and renews the solution inside the tip, which is convenient for corrosion and mass transfer studies. Cyclic voltammetry for the ferrocyanide/ ferrycianide reversible couple under stagnant and flow conditions is reported. Polarization curves under stagnant conditions demonstrate a diffusion control response, while under flow conditions, a steady-state limiting current is observed. An empirical equation to predict mass transfer coefficients as a function of flow conditions and geometric microcell parameters is proposed. Mass transfer coefficients ranged from 4.5 x 10(-6) to 2.5 x 10(-5) m/s. A simulation of the velocity profile inside the plastic micropipette tip describes the outcoming flow inside the tip and the reverse flow.

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There has been considerable interest in the properties of nanocrystalline materials over the last decade. Such materials include metals and alloys with a crystal size within the order of 1 to 100 nm. The interest arises due to the substantial differences in electrical, optical and magnetic properties and also due to their high adsorption capability and chemical reactivity compared to their larger grained counterparts. In this paper, the corrosion of nanocrystalline metals and alloys is investigated and compared to the corrosion of microcrystalline materials having a similar composition. The focus is on the corrosion of nickel, copper, cobalt and iron alloys. Key aspects of different corrosion behaviour such grain boundaries and size are identified.

Paper

Polypyrrole (PPy) films (2 mu m) containing titanate nanotubes (TiNT) were deposited from 0.5 mol dm(-3) pyrrole (Py) and 1 g dm(-3) of TiNT in 0.1 mol dm(-3) aqueous oxalic acid on 904 L stainless steel (SS) 0.1 mm thickness at 298 K. Electron microscopy showed that the nanotubes were adsorbed on the PPy surface and uniformly dispersed in the polymer matrix. The PPy/TiNT composite contained < 10 wt.% titanates which showed an increase of 53% hardness compared with polypyrrole alone. The TINT provide nucleation centres to catalyze the polymerization of pyrrole and can adsorb up to 240 mg g(-1) of the monomer. The corrosion rates for SS. SS/PPy and SS/PPy/TiTN composites, evaluated by linear sweep voltammetry and open-circuit potential measurements in 3% w/v NaCl, were 1.61, 0.008 and 0.004 mg dm(-2) day(-1), respectively, indicating that corrosion rates of stainless steel decreased by up to three orders of magnitude in the presence of the composite films. (C) 2010 Elsevier Ltd. All rights reserved.

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This paper addresses the preparation and characterisation of anticorrosive silane- and polypyrrole-based organic coatings and combinations of the two on aluminium 2024. Layer adsorption studies of organosilanes such as propyl (C3), octyl (C8) and octadecyl (C18) trimethoxysilane and polypyrrole deposits on the aluminium electrodes reveal only limited protection. Their anticorrosive power declines when they are subject to highly corrosive environments, such as salt fog cabinets, for extended periods. The combination of both deposits yields a more protective structure that affords better protection with time. The best performance is achieved with polypyrrole deposits on silanes due to the excellent bonding between the silane adsorbed on the surface of the material and the polypyrrole film. Of the three organosilanes used, the one with the shortest chain performs best. When long-chain organosilanes are used, the polypyrrole film becomes detached due to the lesser interaction between the layers. Electrochemical impedance spectroscopy and morphological studies of the layers also show the greater adhesion and lesser deterioration of polypyrrole deposits on silane layers.

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Electrochemical synthesis of polypyrrole (PPy) on copper electrodes is researched using different techniques. The synthesised films are found to be very adherent and homogeneous. The corrosion behaviour of Cu/PPy is assessed in a 3.5% NaC1 solution using polarisation curves and open circuit potential-time. The relationship between porosity and anticorrosive properties is demonstrated. The chronopotentiometry technique is seen to be the best to produce a good coating that yields good protection against copper corrosion for long immersion times. (c) 2007 Elsevier Ltd. All rights reserved.

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Conducting polypyrrole electrodes were obtained by galvanostatic electropolymerisation on mild steel electrodes from an aqueous solution. The electrochemical response of the coated electrodes in doped and in undoped state was compared with bare mild steel electrodes. The undoped polypyrrole coated electrode offered a noticeable enhancement of protection against corrosion processes. (C) 2004 Elsevier Ltd. All rights reserved.

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Electrodeposition methods have been used to obtain polypyrrole and polyaniline polymer layers, bilayers and blends of these polymers on carbon steel by passivation of the steel surface in the electrodeposition solution (oxalic acid and monomer) between -0.5 and 0.3 V versus Ag/AgCl and subsequent electrodeposition using different techniques (potentiodynamic, galvanostatic and potentiostatic). The results obtained indicate that prepassivation gives rise to adherent polymer layers with excellent corrosion resistance. Of all the bilayers obtained, the best results are yielded with those in which polyaniline is deposited as the base for the deposition of polypyrrole.The electrodeposition of Zn microparticles on the previously deposited polymer layers promotes a great improvement in the corrosion current in highly aggressive solutions such as NaCl due to the effect of Zn as an anodic corrosion inhibitor. The drop in the corrosion rate depends on the amount of Zn deposited on the polymer layer, up to a certain point after which the protective effect ceases to be observed. (c) 2005 Elsevier B.V. All rights reserved.

Paper

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.

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