National Institute Of Materials Physics - Romania

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5714 articles found

2661. Heat transfer process during the crystallization of benzil grown by the Bridgman-Stockbarger method

Authors: Barvinschi, F; Stanculescu, A; Stanculescu, F

Published: FEB 15 2011, JOURNAL OF CRYSTAL GROWTH, 317, 27, DOI: 10.1016/j.jcrysgro.2010.11.028

The temperature distribution and solid-liquid interface shape during benzil growth have been studied both experimentally and numerically. The heat transfer equation with appropriate boundary conditions has been solved by modelling a vertical Bridgman-Stockbarger growth configuration. Two models have been developed, namely a global numerical model and a pseudo-transient approximation in an ideal configuration. (C) 2010 Elsevier B.V. All rights reserved.

2662. Efficient dual functionality of highly porous nanocomposites based on TiO2 and noble metal particles

Authors: Baia, L; Diamandescu, L; Barbu-Tudoran, L; Peter, A; Melinte, G; Danciu, V; Baia, M

Published: FEB 10 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 2678, DOI: 10.1016/j.jallcom.2010.11.154

Porous nanocomposites based on TiO2 aerogels and Au and, respectively, Ag particles were synthesized and their dual functionality to decontaminate water, via photocatalysis, and to detect low concentrations of pollutants from water, via SERS technique, was evaluated using model pollutants. The apparent photodegradation rate constants of a standard pollutant molecule revealed a considerable improvement of the composites photocatalytic performances (even better than one order of magnitude) in comparison with the commercial product Degussa P25. The essential role of the contact between TiO2 and Au nanoparticles was demonstrated and the potential of all synthesized porous composites for photocatalytic experiments with visible light was pointed out. The lowest concentrations of contaminants adsorbed on the noble metal particles detectable by SEAS were found to depend on the composite and pollutant species type and were determined to be between 10(-3) and 5 x 10(-6) M, and 10(-8) and 10(-10) M for off and under resonant excitation, respectively. The morphological (BET, pore size distribution, TEM) and structural (Raman, XRD, diffuse reflectance) particularities of the obtained porous composites were also discussed. (C) 2010 Elsevier B.V. All rights reserved.

2663. Nanometric La0.9Sr0.1Ga0.8Mg0.2O3-x ceramic prepared by low-pressure reactive spark-plasma-sintering

Authors: Borodianska, H; Badica, P; Uchikoshi, T; Sakka, Y; Vasylkiv, O

Published: FEB 3 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 2539, DOI: 10.1016/j.jallcom.2010.11.079

It is proposed a processing route to obtain dense (>= 90%) nanometric La0.9Sr0.1Ga0.8Mg0.2O3-x (LSGM) electrolyte ceramic by reacting under spark-plasma-sintering (SPS) conditions a relatively poor mixture of intermediate powdered La/Sr- and Ga/Mg-based products synthesized separately by precipitation and hydrothermal methods, respectively. Samples with particle size of 9-20, 37-93, and 120-240 nm were measured from the electrical conductivity viewpoint. A fast transport path along grain boundaries was not observed and, a higher nano particle size improves total conductivity in our samples. Results suggest that it is necessary to make a clear distinction between particle size from microscopy observation and crystallite size from structural (e.g. XRD) measurements when looking at the general conductivity - grain size dependence. This dependence is complex and the use of an unconventional, far from equilibrium technique such as SPS might influence it. Currently, a good understanding is missing, but pending on materials, technology specifics and the complex relationship between them, some of the usually promoted ideas from literature such as the necessity of high mixing levels in the precursor powders, of high pressure application during sintering, of low particle size (nano) in the sintered ceramic for a higher conductivity, of high purity phase and so on require careful consideration. (C) 2010 Elsevier B.V. All rights reserved.

2664. Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)-Salen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester

Authors: Protesescu, L; Tudorache, M; Neatu, S; Grecu, MN; Kemnitz, E; Filip, P; Parvulescu, VI; Coman, SM

Published: FEB 3 2011, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 1122, DOI: 10.1021/jp106281z

A dimer chromium(III)-salen complex immobilized on modified silica is an effective catalyst for the epoxidation/epoxide ring-opening reaction of trans-methylcinnamate ester and gave significantly high ee in methyl (2R,3S)-2,3-dihydroxy-3-phenylpropionate. For the first time, it is shown that a donor ligand (e.g., Et3N) can be involved into the enantioselective mechanism of the product configuration. It is suggested that the additive is interacting with the reaction intermediate in a manner that prolongs its lifetime, thus affording a free rotation of the C-C single bond in this species and a selective collapse to the cis-epoxide product. In the presence of water, this epoxide led to methyl (2S,3R)-2,3-dihydroxy-3-phenylpropionate. Alternatively, the donor additives may give rise to a new chromium-based oxidant that effects epoxidation and its consecutive ring opening to diols via an unusual pathway.

2665. Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

Authors: Apostol, I; Stefan, N; Luculescu, CR; Birjega, R; Socol, M; Miroiu, M; Mihailescu, IN

Published: FEB 1 2011, APPLIED SURFACE SCIENCE, 257, 3576, DOI: 10.1016/j.apsusc.2010.11.078

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates. The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements. We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature. (C) 2010 Elsevier B. V. All rights reserved.

2666. Structural changes during the crystallization of the Bi4Ge3O12 glasses

Authors: Polosan, S; Nastase, F; Secu, M

Published: FEB 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 1113, DOI: 10.1016/j.jnoncrysol.2010.10.016

Bismuth-germanate glass ceramics with the composition 40% Bi2O3-60% GeO2 (in molar percents) were prepared through controlled crystallization of melt-quenched glass. The Raman and FTIR spectra recorded in the as-made glasses show broad bands at 240, 400, 780 cm(-1) and 400, 745 cm(-1) have been assigned Ge-O bonds which appear right after preparation. X-ray diffraction has shown that the as-made glasses are amorphous, but after annealing above the crystallization temperature at 558 degrees C, BGO nano-crystallites with a size of about 50 nm precipitate in the glass matrix. The Raman and FTIR spectra reveal sharp peaks associated to the "internal" and "external vibrations" of GeO4 tetrahedral groups inside the BGO nano-crystallites. In the glass ceramic sample the transparency region is shifted at longer wavelengths compared to as-made glass, due to the Rayleigh scattering on the BGO nano-crystallites. (C) 2010 Elsevier B.V. All rights reserved.

2667. Eu3+-doped CaF2 nanocrystals in sol-gel derived glass-ceramics

Authors: Secu, M; Secu, CE; Ghica, C

Published: FEB 2011, OPTICAL MATERIALS, 33, 617, DOI: 10.1016/j.optmat.2010.11.016

Glass-ceramics containing Eu3+-doped CaF2 nanocrystals of about 16 nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2-SiO2 xerogels. In the glass-ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass-ceramics and as a result an additional broad thermoluminescence peak at about 380 degrees C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals. (C) 2010 Elsevier B.V. All rights reserved.

2668. 1-BUTANOL DEHYDRATION AND DEHYDROGENATION OVER VANADIUM ALUMINIUM OXYNITRIDE CATALYSTS

Authors: Florea, M; Delsarte, S; van Keulen, E; Grange, P

Published: FEB 2011, , DOI:

2669. Tailoring immobilization of immunoglobulin by excimer laser for biosensor applications

Authors: Sima, F; Axente, E; Ristoscu, C; Mihailescu, IN; Kononenko, TV; Nagovitsin, IA; Chudinova, G; Konov, VI; Socol, M; Enculescu, I; Sima, LE; Petrescu, SM

Published: FEB 2011, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 96A, 394, DOI: 10.1002/jbm.a.32991

The sheltered transfer and immobilization of rabbit anti-human antiserum immunoglobulin G (IgG) by matrix-assisted pulsed laser evaporation (MAPLE) are reported. The iced targets submitted to laser irradiation consisted of 0.2-2 mg/mL IgG blended or not with lipid (L-a-phosphatidylcholine dipalmitoyl) dissolved in distilled water-based saline buffer. Thin IgG coatings were obtained at room temperature onto glass, fused silica, or silicon substrates. Ten thousand subsequent laser pulses of 0.33, 0.5, or 0.67 J/cm(2) fluence were applied for the synthesis of each sample. Morphology and composition of the thin films were studied by optical, scanning, and atomic force microscopy and Fourier transformed infrared spectrometry. Optical labeling methods such as spectrofluorimetry and fluorescence microscopy were selected to verify the biosensor transduction principle because of their high sensitivity for detecting low amounts of antigen (IgG). Protein immobilization to the substrate surface was demonstrated for all obtained structures after immersion in the donkey anti-rabbit secondary antibody solution. The IgG transfer and immobilization onto substrates were improved by addition of lipid to MAPLE solutions. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 96A: 384-394, 2011.

2670. 'Beautiful' unconventional synthesis and processing technologies of superconductors and some other materials

Authors: Badica, P; Crisan, A; Aldica, G; Endo, K; Borodianska, H; Togano, K; Awaji, S; Watanabe, K; Sakka, Y; Vasylkiv, O

Published: FEB 2011, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 12, DOI: 10.1088/1468-6996/12/1/013001

Superconducting materials have contributed significantly to the development of modern materials science and engineering. Specific technological solutions for their synthesis and processing helped in understanding the principles and approaches to the design, fabrication and application of many other materials. In this review, we explore the bidirectional relationship between the general and particular synthesis concepts. The analysis is mostly based on our studies where some unconventional technologies were applied to different superconductors and some other materials. These technologies include spray-frozen freeze-drying, fast pyrolysis, field-assisted sintering (or spark plasma sintering), nanoblasting, processing in high magnetic fields, methods of control of supersaturation and migration during film growth, and mechanical treatments of composite wires. The analysis provides future research directions and some key elements to define the concept of 'beautiful' technology in materials science. It also reconfirms the key position and importance of superconductors in the development of new materials and unconventional synthesis approaches.