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.

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.

Both Spark Plasma Sintering (SPS) and conventional sintering were applied to obtain bulks of ledeburitic highly alloyed steels for tools fabrication. Powder mixtures of the component elements, of com-pounds or of powders obtained through ball milling of the chips resulting from the processing of parts from steels of interest were used. When compared with traditional technologies (casting and plastic deformation), SPS and the use of milled chips resulted in the formation of microstructures with a high degree of distribution homogeneity and dimensional uniformity of the carbides. As is well known, the improvement of these param-eters leads to the maximization of the functional properties of tools.

A series of niobium-modified aluminum hydroxide fluorides (denoted Nb@AIF(3)), prepared via a fluorolytic sol gel synthesis was investigated for the catalytic one-pot conversion of cellulose to lactic acid. The structure of the new acid catalysts is the result of the dispersion of niobium fluoride in an aluminum hydroxide fluoride matrix. The calcination of the catalysts at a relatively low temperature (350 degrees C) stabilized this structure. Catalytic performances in terms of lactic acid yields are directly correlated with the niobium content.

A rapid high sensitive method for determining the Faraday rotation of optical glasses is proposed. Starting from an experimental setup based on a Faraday rod coupled to a lock-in amplifier in the detection chain, two methodologies were developed for providing reliable results on samples presenting low and large Faraday rotations. The proposed methodologies were critically discussed and compared, via results obtained in transmission geometry, on a new series of aluminophosphate glasses with or without rare-earth doping ions. An example on how the method can be used for a rapid examination of the optical homogeneity of the sample with respect to magneto-optical effects is also provided. (C) 2015 AIP Publishing LLC.

A new methodology for the accurate determination of the specific absorption rate of ferrofluids with magnetite nanoparticles of average size of about 10 nm subjected to alternative current magnetic fields is proposed. A simple numerical compensation of the heating rates by the cooling rates obtained at similar temperatures is employed. Comparisons of the as-obtained adiabatic heating curves with theoretical evaluations are discussed.

The role of iron doping on magnetic properties of hydrothermal anatase TiO2:Fe-57 (0-1 at. %) nanoparticles is investigated by combining superconducting quantum interference device magnetometry with Mossbauer and electron paramagnetic resonance techniques. The results on both as-prepared and thermally treated samples in reduced air atmosphere reveal complexity of magnetic interactions, in connection to certain iron ion electron configurations and defects (oxygen vacancies, F-center, and Ti3+ ions). The distribution of iron ions is predominantly at nanoparticle surface layers. Formation of weak ferromagnetic domains up to 380 K is mainly related to defects, supporting the bound magnetic polaron model. (C) 2015 AIP Publishing LLC.

Bulk ceramics of Ga2S3 and rare-earth sulfides (EuS, Gd2S3, Er2S3) as well as combinations thereof have been prepared by spark plasma sintering (SPS). The disk-shaped ceramics were used as targets for pulsed laser deposition (PLD) experiments to obtain amorphous thin films. The properties of these new bulks and amorphous thin films have been investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), optical transmission spectroscopy, and atomic force microscopy (AFM). In order to test the photoexpansion effect in Gd2S3 and the possibility to create planar arrays of microlenses, the film was irradiated with femtosecond laser pulses at different powers. For low laser power pulses (up to 100mW power per pulse) a photoexpansion effect was observed, which leads to formation of hillocks with a height of 40-50 nm. EuS doped Gd2S3 thin film shows luminescence properties, which recommend them for optoelectronic applications.

The aim of this research is to prepare amorphous thin films of undoped gallium sulphide and doped with rare-earth sulphides, of rare-earth sulphides and to investigate their physical properties. We have prepared thin amorphous films of Ga2S3, EuS, Er2S3, Gd2S3, and Ga2S3 doped with rare-earth sulphides (Ga2S3:EuS, Ga2S3:Er2S3, Ga2S3:Gd2S3) by Pulsed laser Deposition (PLD). The corresponding targets for preparation of amorphous thin films were obtained by Spark Plasma Sintering (SPS) from commercially available powders of binary sulphides. The structural results for the undoped and doped Ga2S3 thin films indicate a packing of disordered layers similar to that of amorphous As2S3. Femtosecond laser irradiation of the Ga2S3 thin films shows a photoexpansion effect at low laser power (85-100 mW) and an ablation effect at higher laser power (above 105 mW). The threshold between low power and high power pulses is situated at higher value for Ga2S3 (100 mW) in comparison with the case of As2S3 thin films (20 mW). (C) 2014 Elsevier B.V. All rights reserved.