National Institute Of Materials Physics - Romania

Publications

911 articles found

481. Laser processing issues of nanosized intermetallic Fe-Sn and metallic Sn particles

Authors: Alexandrescu, R; Morjan, I; Dumitrache, F; Birjega, R; Fleaca, C; Morjan, I; Scarisoreanu, M; Luculescu, CR; Dutu, E; Kuncser, V; Filoti, G; Vasile, E; Ciupina, V

Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9426, DOI: 10.1016/j.apsusc.2012.01.159

Intermetallic Fe-Sn and nanocrystalline metallic Sn nanoparticles have been successfully synthesized from organic precursors using the laser pyrolysis technique with ethylene as sensitizer. Nano-structured Sn (single phase) was prepared by the pyrolysis of Sn(CH3)(4) (TMT) vapors. Controlled Fe/Sn atomic ratios, ranging from 0.69 to 1.64 were obtained for the prepared Fe-Sn nanopowders by the control of Fe(CO)(5) and TMT flows, respectively. XRD studies evidence three main phases: the tetragonal metallic Sn phase and the intermetallic FeSn2 phase and, to a much lesser extent, the cubic ternary carbide Fe3SnC. Complex core-shell structural characteristics were found by HRTEM analysis. More complete information about the Fe phase distributions in the new intermetallic Fe-Sn nanomaterial is provided by temperature dependent Fe-57 Mossbauer spectroscopy. (c) 2012 Elsevier B.V. All rights reserved.

482. Sn-Doped Hydroxylated MgF2 Catalysts for the Fast and Selective Saccharification of Cellulose to Glucose

Authors: Wuttke, S; Negoi, A; Gheorghe, N; Kuncser, V; Kemnitz, E; Parvulescu, V; Coman, SM

Published: SEP 2012, CHEMSUSCHEM, 5, 1711, DOI: 10.1002/cssc.201200303

483. Effect of Nucleators and Intermediates on the Magnetic Properties of Nanosized Magnetite Obtained by Glass Crystallization

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, L; Sandu, E

Published: SEP 2012, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 9, 1545, DOI: 10.1166/jctn.2012.2241

We investigate the role of chromium and phosphorous oxides on the growth and magnetic properties of crystallized Fe-containing borosilicate glasses as well as their evolution under different thermal processing. The glasses have the ratio between SiO2 and Fe2O3 in the range 1.49 to 2.68 and Al2O3/MgO as intermediate/modifier oxides. X-ray diffraction and Mossbauer spectroscopy data revealed the presence of magnetite as the major crystalline phase in all as-prepared samples but additional amounts of hematite and of Fe-rich paramagnetic phases are also visible in some samples. The magnetic response is correlated with the disorder observed in the different sites (tetrahedral and octahedral) of the magnetite.

484. Microwave Synthesis of Fullerene-Doped MgB2

Authors: Plapcianu, C; Agostino, A; Badica, P; Aldica, GV; Bonometti, E; Ieluzzi, G; Popa, S; Truccato, M; Cagliero, S; Sakka, Y; Vasylkiv, O; Vidu, R

Published: AUG 29 2012, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 51, 11010, DOI: 10.1021/ie3005429

Unconventional in situ synthesis of MgB2 undoped and doped with fullerene (C-60) was performed by using a single-mode microwave (MW) furnace. Structural properties suggested that C substitutes for B in the crystal lattice of MgB2, while the J(c) showed typical enhancement at high magnetic fields when C chemical doping occurred. This behavior was similar to published results for another field-activated unconventional method of processing, i.e., spark plasma sintering, and it was opposite to the conventional powder-in-tube method for which chemical substitution was not realized when using addition of C-60. Certain morphologically unique features such as the occurrence of needlelike grains were revealed in the MW samples. Our MW samples showed higher relative density (<= 83%) than previously reported data. Magnetic relaxation experiments suggested the presence of microscopic flux jumps in the MW samples, while macroscopic flux jumps were not observed.

485. A Simple Fabrication of FeSe Superconductors with High Upper Critical Field

Authors: Zhao, PH; Yan, W; Yang, JY; Han, YL; Aldica, G; Sandu, V; Badica, P; Nie, JC

Published: AUG 2012, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 25, 1785, DOI: 10.1007/s10948-012-1540-2

A simple and reproducible fabrication process for the synthesis of FeSe superconductors has been developed. The properties were characterized by X-ray diffraction, scanning electron microscope, superconductivity quantum interference device, and physical property measurement system. It showed a zero resistance superconducting critical temperature of similar to 7.9 K and an onset critical temperature of similar to 13.9 K. The upper critical magnetic field at zero temperature was estimated to be 31 T. The growth mechanism of FeSe flakes was also discussed.

486. Effects of ZnO Nanoparticles on the Wet Scrub Resistance and Photocatalytic Properties of Acrylic Coatings

Authors: Vaja, F; Comanescu, C; Oprea, O; Ficai, D; Guran, C

Published: JUL 2012, REVISTA DE CHIMIE, 63, 726, DOI:

In this work zinc oxide, ZnO, nanopowders were synthesized by co-precipitation method from a zinc acetate, Zn(CH3COO)(2), solution. The obtained nanoparticles were morphologically and structurally characterized by XRD diffraction, SEM, IR and UV-Vis spectroscopy. The new obtained material was investigated as an additive in coatings for improving wet scrub resistance, self-cleaning properties etc. The XRD pattern of the ZnO nanoparticles highlights the wurtzite hexagonal structure and also proves its purity. The correlations made based on their crystallization planes identified ZnO as the sole product. ZnO nanoparticles obtained by co-precipitation method have been introduced by strong shaking in the coating system; this has positively influenced the surface properties of the films.

487. Grain boundary diffusion driven spark plasma sintering of nanocrystalline zirconia

Authors: Borodianska, H; Demirskyi, D; Sakka, Y; Badica, P; Vasylkiv, O

Published: JUL 2012, CERAMICS INTERNATIONAL, 38, 4389, DOI: 10.1016/j.ceramint.2011.12.064

A methodology is proposed to investigate in detail shrinkage kinetics under isothermal spark plasma sintering (SPS) conditions applied to ceramic nano powders such as Y2O3 stabilized ZrO2. To do so, mild SPS conditions were used (low temperatures and pressure, long dwell times). The extracted experimental activation energy has the value of 246 +/- 37 kJ mol(-1) and the slope of the curves on the intense densification stage is around 0.33. Results are in agreement with densification by a grain-boundary diffusion mechanism as for conventional sintering and the contribution from the specific pressure-assisted mechanisms as for hot pressing is insignificant. This result suggests that exploration of mild SPS might prove rewarding in separation and control of the sintering mechanisms leading to production of specific ceramic with new or improved functionality. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

488. Spark plasma sintering of MgB2 in the two-temperature route

Authors: Aldica, G; Batalu, D; Popa, S; Ivan, I; Nita, P; Sakka, Y; Vasylkiv, O; Miu, L; Pasuk, I; Badica, P

Published: JUL 2012, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 477, 50, DOI: 10.1016/j.physc.2012.01.023

Superconducting bulks of MgB2 were obtained by an ex-situ two-temperature route applied to spark plasma sintering (SPS). Processing of samples was performed at lower temperatures than previously reported. Samples produced by the two-temperature route show a higher morphological uniformity, a higher density (above 98%), a higher Vickers hardness, and undesirable stronger microscale flux jumps, as indicated by magnetic relaxation measurements when compared to a sample obtained by the one-temperature route (95.3% relative density). At the same time, all sintered samples show approximately constant crystallite size, critical current density, irreversibility field, critical temperature, weight fraction of impurity phases (MgB4 and MgO), and the amount of carbon accidentally introduced during SPS processing. (C) 2012 Elsevier B.V. All rights reserved.

489. Magnetic glass-ceramics

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Damian, R; Sandu, E

Published: JUN 2012, JOURNAL OF ADVANCED CERAMICS, 1, 143, DOI: 10.1007/s40145-012-0010-4

We present the magnetic properties of magnetic glass ceramics obtained by crystallization of Fe containing borosilicate glass. Two types of nucleators have been used: Cr2O3 and P2O5. The role of the nucleators proved to be crucial in the size and morphology of the crystallites developed within glassy matrix as well in the magnetic response. The former stimulates the growth of regular single crystals uniformly dispersed within the matrix whereas the latter leads to the formation of grains made of tiny (30 nm), nanocrystals. The magnetic response depends on the amount of Fe ions left dispersed within glassy matrix as paramagnetic ions. Although P2O5 leads to the best structural magnetite, almost 42% of Fe ions are left dispersed in the matrix without magnetic interaction. In the case of Cr2O3, the paramagnetic Fe is decreased to 12% but structural deficiency in the occupancy of the Fe sites of magnetite is revealed by Mossbauer spectroscopy.

490. Structure and Magnetic Properties of Nanosized Magnetite Obtained by Glass Recrystallization

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, I; Ghica, C; Sandu, E

Published: JUN 2012, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12, 5050, DOI: 10.1166/jnn.2012.4943

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mossbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.