National Institute Of Materials Physics - Romania

The aim of this paper is to present a reliable procedure for the experimental determination of the specific absorption rate (SAR) in case of superparamagnetic Fe oxide nanoparticles dispersed in liquid environments. It is based on the acquisition of consecutive steps of time-temperature dependences along of both heating and cooling processes. Linear fitting of these recorded steps provides the heating and cooling speeds at different temperatures, which finally allow the determination of the heating profile in adiabatic-like conditions over a broad temperature range. The presented methodology represents on one hand, a useful alternative tool for the experimental evaluation of the heating capability of nanoparticulate systems for magnetic hyperthermia applications and on the other hand, gives support for a more accurate modeling of bio-heat transfer phenomena.

The purpose of the present study is to develop novel nanocomposites based on diglycidylether of bisphenol A (DGEBA) combined with diglycidylether-terminated polydimethylsiloxane (DG-PDMS), reinforced with 10 wt.% (mono-/octa) epoxy POSS nanocages (MEP or OEP-POSS). DG-PDMS and POSS compounds were covalently incorporated into DGEBA resin via copolymerization of epoxy groups. The effect of both DG-PDMS and POSS nanoparticles on the curing reaction, glass transition temperature (T-g), thermal stability, hardness and morphology of DGEBA/DG-PDMS +/- POSS nanocomposites were studied by DSC, FTIR, DMA, TGA, SEM/EDX, AFM and contact angle measurements. SEM/EDX and AFM results prove that OEP-POSS is well dispersed within DGEBA/DG-PDMS polymer matrix, while MEP-POSS forms large POSS aggregates. The thermo-mechanical properties of POSS based nanocomposites are also in good correlation with morphology features. MEP-POSS based nanocomposite with heterogeneous dispersion of FOSS aggregates exhibits lower T-g value and thermal stability in comparison with OEP-POSS nanocomposite which exhibits a nanoscale dispersion of the PUSS cages. The obtained T-g of OEP-POSS based nanocomposite increases with 31 degrees C in comparison with the unreinforced matrix. Moreover, this nanocomposite shows the highest storage modulus (E') and hardness. (C) 2015 Elsevier Ltd. All rights reserved.

High aspect ratio CuO nanowires are synthesized by a simple and scalable method, thermal oxidation in air. The structural, morphological, optical, and electrical properties of the semiconducting nanowires were studied. Au-Ti/CuO nanowire and Pt/CuO nanowire electrical contacts were investigated. A dominant Schottky mechanism was evidenced in the Au-Ti/CuO nanowire junction and an ohmic behavior was observed for the Pt/CuO nanowire junction. The Pt/CuO nanowire/Pt structure allows the measurements of the intrinsic transport properties of the single CuO nanowires. It was found that an activation mechanism describes the behavior at higher temperatures, while a nearest neighbor hopping transport mechanism is characteristic at low temperatures. This was also confirmed by four-probe resistivity measurements on the single CuO nanowires. By changing the metal/semiconductor interface, devices such as Schottky diodes and field effect transistors based on single CuO p-type nanowire semiconductor channel are obtained. These devices are suitable for being used in various electronic circuits where their size related properties can be exploited. (c) 2015 AIP Publishing LLC.

Rh-m-TPPTC complex was successful immobilized onto a hydrotalcite Zn-Al to convert selectively in aqueous media both the symmetric and nonsymmetric alkynes into functionalized alkenes, with boronic acids. The complex preserved its activity after the ionic exchange, leading to excellent results (similar to 87%) for the symmetric alkynes and also for the non-symmetrical alkynes (up to 99%). (C) 2014 Elsevier B.V. All rights reserved.

In this work, the architecture of ZnO particles was found to be changed from nano-whiskers to flowers via the addition of fullerenes in the reaction mixture consisting of zinc chloride, sodium hydroxide and sodium dodecyl sulfate. The change in the morphological structure of ZnO particles is accompanied by a decrease in the photoluminescence (PL) intensity and the appearance of a new Raman line at 1594 cm(-1) that indicates the formation of the compound ZnC60. The growth of the ZnO flower-like particles occurs simultaneously with an aggregation process of C-60 in highly ordered structures, as evidenced in the Raman spectrum by a line at 2934 cm I. A mechanism for the growth of the ZnO flower-like particles is proposed in this work. (C) 2015 Elsevier B.V. All rights reserved.

TiSiC-Ni coatings, with Ni as alloying element, were prepared on Si, C 45, and 316 L steel substrates by cathodic arc technique in a reactive atmosphere of CH4. The coatings, with three different Ni contents (3.2, 6.8 and 16.2 at.%), were investigated in terms of microchemical and microstructural properties, mechanical characteristics and tribological performance using energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, hardness and adhesion measurements, and ball-on disc tribological testing. The coatings were found to consist of a mixture of different phases: face-centred cubic crystalline carbide, metallic Ni, and amorphous Si and C, with relative amounts depending on Ni concentration. All of the coatings exhibited dense and featureless morphologies. Ni addition to TiSiC coatings led to residual stress reduction (from -0.50 to -0.59 GPa) and improved adhesion strength (in the range 44-46 N). The TiSiC-Ni coatings with Ni contents below 7 at.% exhibited the best tribological properties under dry conditions (friction coefficients of similar to 0.32; wear rates from 3.16 to 3.66 x 10(-6) mm(3) N-1 m(-1)).

Ferroelectric/electric properties of PbZr0.52Ti0.48O3 (PZT) thin films grown by pulsed laser deposition (PLD) on two different substrates, Si (001) and SrTiO3 (STO) (001), were comparatively analyzed. The structural characterization has revealed the epitaxial relationship between the grown layers and the two types of substrates, with larger density of structural defects for the films deposited on Si (001) with buffer STO layer. The ferroelectric/electric properties are also different, with lower remnant polarization (about half of the value obtained on STO substrate), higher dielectric constant (about two times larger), and lower leakage current (about two orders of magnitude lower) for the PZT films deposited on Si (001) compared to those deposited on (001) STO substrates. Nevertheless, the results show that the use of a STO buffer layer on Si can be a solution to obtain good quality PZT capacitor structures without using expensive single-crystal oxide substrates. In this way, applications based on PZT capacitors (e.g. non-volatile memories, pyroelectric detectors, light switches, etc.) would be more easily integrated directly on Si wafers.

Ca3-xBaxCo4O9 bulk polycrystalline thermoelectric ceramics with x = 0.00, 0.01, 0.03 and 0.05 have been prepared through a classical solid state method. Microstructural characterizations of sintered samples have shown that Ba has been incorporated into the Ca3Co4O9 and/or Ca3Co2O6 structures and that no Ba-based secondary phases have been produced. The apparent density values increase when the amount of barium is raised with respect to the undoped samples, reaching a maximum value of around 77 % of the Ca3Co4O9 theoretical density, for samples with the highest amount of barium. Electrical resistivity of doped samples decreases in the whole measured temperature range with respect to the undoped ones, while Seebeck coefficient remains practically unchanged. In conclusion, the improvement in resistivity leads to power factor values which are higher than the ones measured in undoped samples, fact which makes this bulk polycrystalline compound a promising candidate for high-temperature power generation applications in oxidative environments.

Hard carbon thin films were synthesized on Si (100) and quartz substrates by the Pulsed Laser Deposition (PLD) technique in vacuum or methane ambient to study their suitability for applications requiring high mechanical resistance. The deposited films' surface morphology was investigated by scanning electron microscopy, crystalline status by X-ray diffraction, packing and density by X-ray reflectivity, chemical bonding by Raman and X-ray photoelectron spectroscopy, adherence by pull-out measurements and mechanical properties by nanoindentation tests. Films synthesized in vacuum were a-C DLC type, while films synthesized in methane were categorized as a-C:H. The majority of PLD films consisted of two layers: one low density layer towards the surface and a higher density layer in contact with the substrate. The deposition gas pressure played a crucial role on films thickness, component layers thickness ratio, structure and mechanical properties. The films were smooth, amorphous and composed of a mixture of sp(3)-sp(2) carbon, with sp(3) content ranging between 50% and 90%. The thickness and density of the two constituent layers of a film directly determined its mechanical properties.

The recovery of the catalysts from the reaction mixture and their recycling is important goals of the current applied catalysis. The stringent ecological and economical demands for sustainability made this concern even more important for the solid catalysts used in the area of biomass catalytic transformations where the raw material usually is not soluble in most of the organic solvents. Therefore, the solid catalyst cannot be easily separated from the mixture of untransformed raw material and by-products (e. g., humines). However, these goals can be achieved by using magnetic nanoparticles (MNPs) based catalysts. This study reports on the magnetic response of two types of new magnetic nanocomposite catalytic systems, Ru@MNP and Nb@AlF3, used in the synthesis of sorbitol/glycerol and of lactic acid, respectively, by direct cellulose degradation. The results showed that the recovering possibilities of the Nb@AlF3 catalysts, with a weaker magnetic response associated to the so called diluted magnetic oxide systems, are much diminished as compared to Ru@MNP, where the magnetic response is generated using MNP supported catalysts. (C) 2015 AIP Publishing LLC.