National Institute Of Materials Physics - Romania

Publications

892 articles found

411. Volume fraction dependent magnetic behaviour of ferrofluids for rotating seal applications

Authors: Schinteie, G; Palade, P; Vekas, L; Iacob, N; Bartha, C; Kuncser, V

Published: OCT 2 2013, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 46, DOI: 10.1088/0022-3727/46/39/395501

Ferrofluid samples consisting of magnetite nanoparticles (NPs) coated with oleic acid and dispersed in a non-polar organic solvent have been synthesized by chemical routes. Different volume fractions, phi, of magnetic NPs were considered. The overall structural characterization of NPs has been performed by x-ray diffractometry, with lattice parameters and average coherence lengths evaluated via Rietveld refinements. The magnetic properties of different samples have been analysed by SQUID magnetometry and temperature-dependent Mossbauer spectroscopy and finally explained by adequate magnetic relaxation mechanisms. Zero field cooling-field cooling protocols provided useful information about specific volume fraction dependent magnetic relaxation and de-freezing processes, the lack of the Verwey transition and stronger dipolar interactions at higher volume fractions. Anisotropy energies as obtained by both temperature dependent Mossbauer spectroscopy and magnetometry data are compared and a new procedure for a quantitative characterization of the dipolar interactions is proposed.

412. Direct sintering of SiC-W composites with enhanced thermal conductivity

Authors: Galatanu, M; Popescu, B; Enculescu, M; Tiseanu, I; Craciunescu, T; Galatanu, A

Published: OCT 2013, FUSION ENGINEERING AND DESIGN, 88, 2602, DOI: 10.1016/j.fusengdes.2013.05.036

Different types of SiC-W composites have been realized by spark plasma sintering in a single step process starting with beta SiC nanometric powder, W nanometric and micrometric sized powders, and W foils. SEM, EDX, XRD and X-ray tomography have been used to analyze the sample morphology while the thermal properties of the resulting materials have been investigated up to 1000 degrees C using a LFA thermal analyzer. The results show the possibility to produce dense W-SiC composites, with enhanced thermal conductivity using a relatively simple route. (C) 2013 Elsevier B.V. All rights reserved.

413. Room and high temperature toughening in directionally solidified B4C-TiB2 eutectic composites by Si doping

Authors: Bogomol, I; Badica, P; Shen, YQ; Nishimura, T; Loboda, P; Vasylkiv, O

Published: SEP 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 570, 99, DOI: 10.1016/j.jallcom.2013.03.084

Directionally solidified B4C-TiB2 eutectics doped with different Si contents were prepared by floating zone method. Silicon doping (up to 3 vol.%) promotes a more coherent interface between B4C matrix and TiB2 inclusions, a decrease of the spacing between TiB2 (when solidification rate is constant), and formation of a more uniform morphology with thinner inclusions. These features lead to simultaneous enhancement of Vickers hardness (HV), fracture toughness (K-1c) and bending strength (sigma) when compared with Si-free B4C-TiB2 eutectics. For our materials, the average HV, K-1c and sigma were 45.2 GPa, 7.04 MPa m(1/2), and 460 MPa at room temperature or 487 MPa at 1600 degrees C, respectively. The values of sigma at indicated temperatures are approximately twice higher than for the Si-free B4C-TiB2 eutectic composites. (C) 2013 Elsevier B.V. All rights reserved.

414. Detailed characterization of functionalized magnetite and ascertained effects

Authors: Culita, DC; Patron, L; Oprea, O; Bartha, C; Palade, P; Teodorescu, V; Filoti, G

Published: SEP 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1916-7

The paper reports on magnetite successfully functionalized with two new molecules. The investigations, involving chemical and physical methods, provided relevant features involving cell parameters and grain sizes, or the intermingling ratio between magnetite and functionalizing molecules, as deduced from magnetic measurements. A large amount of interesting data concerning various surface and local interaction mechanisms was supplied by detailed Mossbauer measurements. The new outputs are explained in terms of material processing and intimate mixing of the involved molecules.

415. Novel Fe@C-TiO2 and Fe@C-SiO2 water-dispersible magnetic nanocomposites

Authors: Fleaca, CT; Dumitrache, F; Morjan, I; Alexandrescu, R; Luculescu, C; Niculescu, A; Vasile, E; Kuncser, V

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 288, DOI: 10.1016/j.apsusc.2013.01.172

We report the synthesis of novel nanocomposites based on Fe@C nanoparticles obtained from Fe(CO)(5) and C2H4/H-2 by laser pyrolysis technique using a three nozzles injector. The alpha Fe-FexCy@C particles (below 24 nm diameter) were first functionalized with hydrophilic groups using Na carboxymethylcellulose. Oxidic precursors (Si(OC2H5)(4) or Ti(OC2H5)(4)) dissolved in ethanol were mixed with ethanolic suspensions of hydrophilized Fe@C nanoparticles using strong ultrasonication, then with water (at different pH values) and finally the Fe-containing composites were recovered by magnetic separation. The SiO2 and TiO2-coated powders were characterized by XRD, FT-IR and TEM techniques and their magnetic hysteresis curves were recorded at different temperatures. Both composites contain submicron aggregates of Fe@C nanoparticles embedded in/surrounded by a disordered porous oxidic matrix/shell. Near superparamagnetic behavior and room temperature and 26 Am-2/kg (for Fe@C/SiO2) or 57Am(2)/kg (for Fe@C/TiO2) saturation magnetization values were recorded and a blocking temperature around 500K was extrapolated. (C) 2013 Elsevier B.V. All rights reserved.

416. Magnetic configurations of Ni-Cu alloy nanowires obtained by the template method

Authors: Matei, E; Enculescu, I; Toimil-Molares, ME; Leca, A; Ghica, C; Kuncser, V

Published: AUG 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1863-3

High aspect ratio nanowires of Ni-Cu alloys have been synthesized by potentiostatic electrochemical deposition in etched ion-track membranes. The nickel-to-copper ratio in the nanowires was controlled via the deposition potential and electrochemical bath composition. We present a detailed study of nanowire properties including morphology, composition, and magnetic behavior. We report the magnetic configurations measured as function of the nanowire composition and discuss domain formation, anisotropy aspects, and local easy axis distributions.

417. Spectroscopic Investigation of Iron Substitution in EuCoO3: Related Impact on the Catalytic Properties in the High-Temperature N2O Decomposition

Authors: Wu, Y; Dujardin, C; Granger, P; Tiseanu, C; Sandu, S; Kuncser, V; Parvulescu, VI

Published: JUL 11 2013, JOURNAL OF PHYSICAL CHEMISTRY C, 117, 13999, DOI: 10.1021/jp402211c

418. Magnetic properties of iron-carbon nanocomposites obtained by laser pyrolysis in specific configurations

Authors: Schinteie, G; Kuncser, V; Palade, P; Dumitrache, F; Alexandrescu, R; Morjan, I; Filoti, G

Published: JUL 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 564, 34, DOI: 10.1016/j.jallcom.2013.02.126

New nanometric systems were produced by using specific parameters of the laser pyrolysis process. Relevant results related to the magnetic behavior of the samples were obtained via SQUID magnetometry and Mossbauer spectroscopy, the data being corroborated with those previously obtained from X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The formed nanocomposites contain iron carbides, iron oxides and metallic iron nanoparticles which relative content and average size depend strongly on experimental specific parameters of the pyrolysis process. The magnetic properties and the local interaction mechanisms were explained by adequate magnetic relaxation and static models. (C) 2013 Elsevier B.V. All rights reserved.

419. Magnetic properties of BaxSr1-xFe12O19 (x=0.05-0.35) ferrites prepared by different methods

Authors: Cernea, M; Sandu, SG; Galassi, C; Radu, R; Kuncser, V

Published: JUN 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 561, 128, DOI: 10.1016/j.jallcom.2013.01.081

Hexagonal ferrites BaxSr1-xFe12O19 (x = 0.05, 0.15, 0.25, 0.35) were prepared by sol-gel and conventional solid state reaction techniques. Their magnetic properties, investigated by magnetometry and Mossbauer spectroscopy, were discussed in correlation to structural aspects. Whereas the hexaferrites obtained by sol-gel are almost single phase, the ones prepared by the conventional solid state reaction technique present a low amount of BaFe2O4 as secondary phase. All samples show a relative high coercive field and remanent magnetization, as specific features for permanent magnet behavior. The five Fe3+ sites of the specific elemental cell have been revealed and their relative occupancy has been derived from the Mossbauer spectra. The analyzed samples show a sensitivity of the magnetic properties (magnetic moment and anisotropy) with respect to the occupancy of the different Fe sites. (C) 2013 Elsevier B. V. All rights reserved.

420. Structural changes during toluene complete oxidation on supported EuFeO3 monitored by in situ Eu-151 and Fe-57 Mossbauer spectroscopy

Authors: Florea, M; Alifanti, M; Kuncser, V; Parvulescu, VI

Published: JUN 1 2013, CATALYSIS TODAY, 208, 59, DOI: 10.1016/j.cattod.2012.09.035

Pure EuFeO3 and ceria were prepared via a sol-gel citrate route and were calcined at 700 degrees C. Separately, a 20 wt% EuFeO3/CeO2 was prepared via incipient wetness impregnation of calcined ceria with citrate precursors and calcined in the same conditions. SBET, XRD, toluene chemisorption, toluene-TPD and in situ Eu-151 and Fe-57 Mossbauer investigations were performed. All characterization data indicate the formation of a well-dispersed EuFeO3 at the surface of CeO2. During the oxidation of toluene Eu-151 and Fe-57 Mossbauer spectroscopy suggested a cooperative effect of the cations. The catalysts were tested in total oxidation of toluene. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuFeO3. All structural changes during operation time were reversible. (C) 2012 Elsevier B.V. All rights reserved.