National Institute Of Materials Physics - Romania

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5781 articles found

3351. Iron oxide colloids and their heterogenization by silica sol-gel entrapment: Catalytic and magnetic properties

Authors: Neatu, F; Kraynov, A; D'Souza, L; Parvulescu, VI; Kranjc, K; Kocevar, M; Kuncser, V; Richards, R

Published: AUG 31 2008, APPLIED CATALYSIS A-GENERAL, 346, 35, DOI: 10.1016/j.apcata.2008.04.024

Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe304). These colloids, both as 'quasi-homogenous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). (C) 2008 Published by Elsevier B.V.

3352. Structural and hydrogen absorption/desorption properties of YNi(4-x)Al(x)Mg compounds (with 0 <= x <= 1.5)

Authors: Stan, C; Andronescu, E; Predoi, D; Bobet, JL

Published: AUG 11 2008, JOURNAL OF ALLOYS AND COMPOUNDS, 461, 234, DOI: 10.1016/j.jallcom.2007.07.064

The compounds YNi(4-x)Al(x)Mg with 0 <= x <= 1.5, crystallizing in the C15 structure type (MgCu(4)Sn-type), have been elaborated by mechanical milling and a subsequent heat treatment at 650 degrees C for 1 h. It was possible to synthesize the compounds YNi(4-x)Al(x)Mg with x up to approximately 1.15 and the lattice parameters was in good agreement with those already reported. All the samples, excepting the YNi(4)Mg compound, absorbed and desorbed hydrogen reversibly and no structural change is reported after the hydrogenation. A direct relationship between the lattice parameters and the equilibrium plateau pressure was found. (C) 2007 Elsevier B.V. All rights reserved.

3353. Phase diagram of a lattice of vortex molecules in multicomponent superconductors and multilayer cuprate superconductors

Authors: Tanaka, Y; Shivagan, DD; Crisan, A; Iyo, A; Shirage, PM; Tokiwa, K; Watanabe, T; Terada, N

Published: AUG 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/8/085011

The Abrikosov lattice in the multilayer cuprate superconductor CuBa2Ca3Cu3Oy (Cu-1223) has been experimentally and theoretically demonstrated to be composed of vortex molecules. Cu-1223 is considered to be a typical multicomponent superconductor. We show that in such a system the rotational freedom around the axis of the vortex molecular tube generates orientational disorder and the orientational glass (or crystal) phase, which is never present in conventional vortex lattices consisting of axisymmetric vortices. The emergence of the orientational glass phase and orientational order phase with orthorhombic distortion is a general property of vortex molecule lattices of the multiband type of multicomponent superconductors.

3354. Calcium phosphate ceramics for biomedical applications

Authors: Predoi, D; Vatasescu-Balcan, RA; Pasuk, I; Trusca, R; Costache, M

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2155, DOI:

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper describes the synthesis of calcium phosphate ceramics powders via a sol-gel method, The powders were sintered at 600 and 800 degrees C. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used for characterization and evaluation of the phase composition, morphology and particle size of samples, The functional group of the coatings were analyzed using Fourier transform infrared (FTIR). The XRD analysis revealed a well crystallized HA structure at both temperatures. At 800 degrees C a small amount of CaO (about 0.4%) was detected. The mean crystallite size, determined from the breadth of the diffraction lines, increases from 30 nm at 600 degrees C to about 110 nm at 800 degrees C. FTIR spectra showed the presence of various PO43- and OH- groups present in the powders. Osteoblast cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics, by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) assay. We note that the viability of HAp-600 starts to decrease after 12h, while the viability of HAp-800 decreases after 6h.

3355. Fe-catalyzed carbon nanotubes growth on fluidized powders by remote radiofrequency plasma beam

Authors: Vizireanu, S; Stoica, D; Birjega, R; Ghica, C; Teodorescu, V; Nistor, L; Ganea, R; Dinescu, G

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2060, DOI:

The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.

3356. The study of passive film formed on 316L stainless steed surface for orthopedic implant applications

Authors: Bebicu, I; Samide, A; Oprea, B; Tutunaru, B

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2158, DOI:

The characterization of passive films formed on 316L stainless steel surface implanted in a femur for 1 year is discussed according to Mossbauer Spectroscopy and scanning electron microscopy (SEM).The Mossbauer spectroscopy shown that surface layer consist mainly of oxidic species and suggested a possible apparition of a ferrite phase on surface In according to Mossbauer Spectroscopy, SEM shown that during implantation a change in the superficial microstructure took place and a corrosion process was presently.

3357. The CMS experiment at the CERN LHC

Authors: Chatrchyan, S; Hmayakyan, G; Khachatryan, V; (...) Lungu, GA; (...) Onengut, G (CMS Collaboration)

Published: AUG 2008, JOURNAL OF INSTRUMENTATION, 3, S08004, DOI: 10.1088/1748-0221/3/08/S08004

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

3358. Structure and dielectric properties of HfO2 films prepared by a sol-gel route

Authors: Blanchin, MG; Canut, B; Lambert, Y; Teodorescu, VS; Barau, A; Zaharescu, M

Published: AUG 2008, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 47, 172, DOI: 10.1007/s10971-008-1758-4

Mono- and multilayer HfO2 sol-gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 degrees C for 0.5 h (after drying at 100 degrees C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 degrees C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 degrees C the films are totally crystallized. The HfO2 grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO2 layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.

3359. Optica and structural properties of polythiophene-like films deposited by plasma polymerization

Authors: Galca, AC; Satulu, V; Ionita, MD; Bercu, M; Barna, E; Dumitru, M; Mitu, B; Dinescu, G

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2037, DOI:

Polymer-like organic thin films obtained by plasma techniques are of wide interest for various applications. Polythiophene-like thin films were deposited by plasma polymerization in a parallel plate radiofrequency reactor starting from thiophene vapors. The optical properties of the films were obtained from spectroscopic ellipsometry, in the 250-1250 nm range. The calculated band gap is in agreement with a polythiophene-like material consisting of cross-linking of oligomers. The presence of functional groups and film stability against oxidation is analyzed by FTIR spectrometry. The monitoring of functional groups incorporation during the film deposition was done by analyzing the integral intensities of specific absorption bands and led to the conclusion that homogeneous films are obtained whatever the process duration.

3360. A simple and efficient route to active and dispersed silica supported palladium nanoparticles

Authors: Barau, A; Budarin, V; Caragheorgheopol, A; Luque, R; Macquarrie, DJ; Prelle, A; Teodorescu, VS; Zaharescu, M

Published: AUG 2008, CATALYSIS LETTERS, 124, 214, DOI: 10.1007/s10562-008-9465-x

Various mesoporous silica supported Pd materials were prepared by different methodologies in order to control and optimize the metal nanoparticle sizes for catalytic applications. The catalytic activities (conversion, mol% and selectivity to methyl-cinnamate) of the supported palladium catalysts were investigated in the Heck reaction under microwave irradiation using various haloarenes. Pd materials prepared by co-precipitation exhibited a very poor activity in the Heck reaction compared to that of Pd impregnated samples. Impregnated materials prepared without the use of a specific reducing agent had comparable activities to those of APTS-NaBH4 reduced Pd materials, validating the simplicity of the methodology. High selectivities to methylcinnamate were obtained for all materials.