National Institute Of Materials Physics - Romania

We have studied the one-step procedure for simultaneous synthesis and sintering of SiC-doped MgB2 by the spark plasma sintering technique. Two types of composition, one in which Mg is strongly deficient, with the atomic ratio , and one in which Mg content is slightly higher than the stoichiometric value, specifically , were investigated. The amount of SiC was 12 wt.% and 9 wt.%, respectively. For comparison we also studied the way the deficit of Mg can be compensated in a second process of sintering. The sample with Mg deficit shows that SiC is left almost unreacted but the results are spectacular: the highest critical temperature, 36.5 K, the highest upper critical field and the highest self-field critical current density 6.7x10(5) A/cm(2) at 10 K. In the sample with overstoichiometric Mg, SiC is decomposed, carbon diffuses within MgB2 but the critical temperature is only of 35.8 K and the zero-field critical current density is one order of magnitude lower. The compensation of the deficit of Mg in the two-step procedure is not efficient. The critical temperature is even lower, 35.8 K, the upper critical field is also lower despite SiC decomposition and C diffusion within MgB2 and the critical current density is slightly above 10(5) A/cm(2). However, at low temperatures and fields of order 7 T the sample with overstoichiometric Mg and the sample prepared by the two-step procedure have higher critical current density.

The influence of different ions NO3 (-) and SO4 (2-) on the carbon steel corrosion in ammonium chloride was investigated using mass loss measurements and potentiodynamic polarization. Corrosion products were analyzed using X-ray photoelectron spectroscopy (XPS) and simultaneous thermal and differential scanning calorimetry (TG/DSC). XPS analysis shows that the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) and FeO(OH) containing inclusions of these anions, species such as Fe3+O(OH,Cl-); Fe3+O(OH,SO4 (2-)); and Fe3+O(OH,NO3 (-)). TG/DSC confirms the decomposition of the rusty products formed by chemical corrosion, compounds like Fe3+ oxyhydroxides, with beta-FeOOH as the major phase, crystal structure of which may contain Cl-, NO3 (-), and SO4 (2-)-e.g., akaganeite [Fe3+O(OH,A)].

The Griess assay has been used to determine the possible changes in the measured NO2- concentrations induced by TiO2 nanoparticles in three types of nitrite-containing samples: aqueous NaNO2 solutions with known concentrations, and two types of cell culture media-Roswell Park Memorial Institute medium (RPMI-1640) and Dulbecco's Modified Eagle Medium (DMEM-F12) used either as delivered or enriched in NO2- by NaNO2 addition. We have used three types of titania with average particle sizes between 10 and 30 nm: Degussa P25 and two other samples (undoped and Fe3+-doped anatase TiO2) synthesised by a hydrothermal route in our laboratory. The structural, morphological, optical and physicochemical characteristics of the used materials have been studied by X-ray diffraction, transmission electron microscopy (EDX), Mossbauer spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV-Vis reflectance spectroscopy, dynamic light scattering and diffuse reflectance infrared Fourier transform spectroscopy. The opacity and sedimentation behaviour of the studied TiO2 suspensions have been investigated by photometric attenuance measurements at 540 nm. To account for the photocatalytic properties of titania in a biologically relevant context, multiple Griess tests have been performed under controlled exposure to laboratory natural daylight illumination. The results show significant variations of light attenuance (associated with NO2- concentrations in the Griess test) depending on the opacity, sedimentation behaviour, NO2- adsorption and photocatalytic properties of the tested TiO2 nanomaterials. These findings identify material characteristics recommended to be considered when analysing the results of Griess tests performed in biological studies involving TiO2 nanoparticles.

Trace amounts of substitutional Mn2+ ions and shallow donors magnetic centers were identified by electron paramagnetic resonance (EPR) in crystalline Zn(OH)(2) prepared by precipitation of a Zn-nitrate solution with NaOH. Strong changes in the Mn2+ ions spectrum, as well as a sharp increase in the concentration of the shallow donor centers were observed by EPR in the 110-140 degrees C temperature range, during pulse annealing experiments in air up to 240 degrees C. They reflect the decomposition of the crystalline Zn(OH)(2) host lattice into nanocrystalline ZnO, confirmed by X-ray diffraction and thermal analysis measurements. Accurate spin Hamiltonian parameters of the observed paramagnetic centers were determined by lineshape simulation and fitting of the EPR spectra, to be used as reference data in further studies of nanocrystalline systems involving Zn(OH)(2). (C) 2012 Elsevier B.V. All rights reserved.

Due to the growing importance of low concentrated pollution of surface, ground and drinking, the photocatalytic decomposition of ibuprofen down to low ppm concentrations over titania catalyst has been investigated in detail. The catalyst was characterized by XRD, TEM, diffuse reflection UV-Vis and nitrogen adsorption measurement. The photocatalytic abatement of ibuprofen was monitored by UV-Vis spectrometry, chromatographic by GC/MS, and HPLC coupled electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Catalytic performance has been studied by varying the catalyst and substrate concentration as well as decreasing the catalyst-to-substrate mass ratio over a wide range. The photocatalytic treatment with titania catalyst leads to rapid mineralization of ibuprofen. Formation of intermediate reaction products has been investigated. It is proposed that intermediates in part form oligomeric species, which are responsible for catalyst poisoning. Additional, the influence of the pH value, oxygen supply and catalyst re-use have been checked. (C) 2012 Elsevier B.V. All rights reserved.

We report on the synthesis of novel ovine and bovine derived hydroxyapatite thin films on titanium substrates by pulsed laser deposition for a new generation of implants. The calcination treatment applied to produce the hydroxyapatite powders from ovine/bovine bones was intended to induce crystallization and to prohibit the transmission of diseases. The deposited films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. Pull-off adherence and profilometry measurements were also carried out. X-ray diffraction ascertained the polycrystalline hydroxyapatite nature of the powders and films. Fourier transform infrared spectroscopy evidenced the vibrational bands characteristic to a hydroxyapatite material slightly carbonated. The micrographs of the films showed a uniform distribution of spheroidal particulates with a mean diameter of similar to 2 mu m. Pull-off measurements demonstrated excellent bonding strength values between the hydroxyapatite films and the titanium substrates. Because of their physical-chemical properties and low cost fabrication from renewable resources, we think that these new coating materials could be considered as a prospective competitor to synthetic hydroxyapatite used for implantology applications. (C) 2012 Elsevier B.V. All rights reserved.

We have investigated the impact of the self-consistent coaction of carrier-phonon and Coulomb interactions on the scattering efficiency in a quantum-dot system within a quantum kinetic theory. While there is a substantial effect on the scattering between discrete quantum-dot states due to the interplay of both interactions, the capture of carriers from a wetting layer is only slightly enhanced by the coaction. For the carrier capture due to the electron-phonon interaction, results of the quantum kinetic treatment are compared to those of a perturbative approach. DOI: 10.1103/PhysRevB.87.035301

ZnO uniform films were deposited on polymer sphere arrays by an electroless technique. The low-dimensional ZnO particles were grown from an aqueous solution of zinc nitrate and dimethylamineborane. The X-ray diffraction studies demonstrate that the ZnO crystallites have a hexagonal wurtzite structure. The scanning electron microscopy images prove that ZnO hexagonal prisms are synthesized with a fairly uniform diameter of around 200 nm. From the contact angle measurements it was found that the electroless deposition on polymer sphere arrays of semiconductor hexagonal prisms leads to an improvement of ZnO hydrophobic properties.

Dense superconducting composites with magnetic nanoparticles were prepared by spark plasma sintering. In addition to structure and magnetic properties, we focused on the pinning properties as described by the field and temperature dependence of the scaled pinning force analyzed. We found that the pinning force does not obey any scaling law and attributed this effect to the anisotropy of the MgB2 and the almost random distribution of the orientation of the superconducting grains within the polycrystalline sample.

A combined chemical-electrochemical method was used for covalent functionalization of single-walled carbon nanotube (SWNT) with polydiphenylamine (PDPA) doped with heteropolyanions of H3PMo12O40 center dot xH(2)O. The functionalization process induces in Raman spectra of SWNTs the following changes: (i) an increase in relative intensity of the D band, accompanied a gradual up-shift of the G band in the case of the semiconducting tubes and a decrease in the relative intensity of band peaked at 1540 cm(-1) is remarked in the case of the metallic tubes; (ii) in the anti-Stokes Raman spectrum an increase in the relative intensity of Raman line of metallic tubes peaked at -1560 cm(-1) is remarked when the cycles number increases. The additional down-shift of the FTIR bands belonging to H3PMo12O40 heteropolyanions (at 881, 943 and 1055 cm(-1)) and PDPA (at 688, 736 and 1016 cm(-1)) originates in hindrance steric effects induced the covalent functionalization of SWNTs with polymer molecules. Using Raman scattering and FTIR spectroscopy we demonstrate that chemical polymerization of diphenylamine in the presence of H3PMo12O40 center dot xH(2)O and SWNTs results in a composite of the type blend based on PDPA in un-doped state and SWNTs doped with H3PMo12O40 heteropolyanions. (C) 2012 Elsevier Inc. All rights reserved.