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Taca M.,METAV CD | Daisa D.,METAV CD | Geanta V.,Polytechnic University of Bucharest | Stefanoiu R.,Polytechnic University of Bucharest | And 2 more authors.
Materials Today: Proceedings | Year: 2017

The micro alloyed steels proved to be reliable materials for the forged automotive parts because of their high strength in as normalized condition. However their use is limited at parts non subjected to impact because the toughness of such a material is relatively low. In order to improve the mechanical characteristics, deformability, strength and toughness, researches focused on the micro alloying content (especially Nb and V) and on processing parameters. The present research aimed at obtaining new micro alloyed steels having improved toughness in as forged/normalized condition. The influence of the chemical composition (Nb/Ti ratio) and of forging parameters as cooling speed and reduction degree were analyzed. For given amounts and ratio of V and Nb, very good mechanical and structural properties were obtained. The tests have been performed on forged parts and bars. © 2017 Elsevier Ltd. All rights reserved.

Galateanu B.,University of Bucharest | Dimonie D.,Romanian National Institute for Research and Development in Chemistry and Petrochemistry | Vasile E.,METAV CD | Nae S.,Emergency Hospital of Plastic Surgery and Burns | And 2 more authors.
BMC Biotechnology | Year: 2012

Background: The reconstruction of adipose tissue defects is often challenged by the complications that may occur following plastic and reconstructive surgery, including donor-site morbidity, implant migration and foreign body reaction. To overcome these problems, adipose tissue engineering (ATE) using stem cell-based regeneration strategies has been widely explored in the last years. Mounting evidence has shown that adipose-derived stem cells (ADSCs) represent a promising cell source for ATE. In the context of a small number of reports concerning adipose tissue regeneration using three-dimensional (3-D) systems, the present study was designed to evaluate the biological performance of a novel alginate matrix that incorporates human ADSCs (hADSCs).Results: Culture-expanded cells isolated from the stromal vascular fraction (SVF), corresponding to the third passage which showed the expression of mesenchymal stem cell (MSC) markers, were used in the 3-D culture systems. The latter represented a calcium alginate hydrogel, obtained by the diffusion of calcium gluconate (CGH matrix), and shaped as discoid-thin layer. For comparative purposes, a similar hADSC-laden alginate hydrogel cross-linked with calcium chloride was considered as reference hydrogel (RH matrix). Both hydrogels showed a porous structure under scanning electron microscopy (SEM) and the hADSCs embedded displayed normal spherical morphologies, some of them showing signs of mitosis. More than 85% of the entrapped cells survived throughout the incubation period of 7 days. The percentage of viable cells was significantly higher within CGH matrix at 2 days post-seeding, and approximately similar within both hydrogels after 7 days of culture. Moreover, both alginate-based hydrogels stimulated cell proliferation. The number of hADSC within hydrogels has increased during the incubation period of 7 days and was higher in the case of CGH matrix. Cells grown under adipogenic conditions for 21 days showed that both analyzed 3-D culture systems support adipogenic differentiation in terms of neutral lipid accumulation and perillipin expression. Furthermore, the cells encapsulated in CGH matrix displayed a more differentiated phenotype.Conclusions: The results of this study suggest that both CGH and RH matrices successfully support the survival and adipogenesis of hADSC. An enhancement of biological performance was detected in the case of CGH matrix, suggesting its promising application in ATE. © 2012 Galateanu et al;licensee BioMed Central Ltd.

Sima M.,National Institute of Materials Physics Bucharest | Vasile E.,METAV CD | Sima A.,Romanian National Institute for Lasers, Plasma and Radiation Physics
Digest Journal of Nanomaterials and Biostructures | Year: 2013

Electrophoretic deposition (EPD) method is employed to obtain a thick ZnO layer on a ZnO nanorod array prepared in a hydrothermal-electrochemical process. ZnO nanorods have the role to improve the mechanical stability and adherence of ZnO layer deposited by electrophoretic technique. D149 dye is used as sensitizer for ZnO semiconductor. The thus prepared ZnO layer is used for the photoanode of dye-sensitized solar cell (DSC). Performance parameters were extracted from standard current-voltage characteristic (I-V) and charge transfer phenomena occurring at ZnO/dye/electrolyte was evaluated by electrochemical impedance spectroscopy (EIS).

Matei E.,Polytechnic University of Bucharest | Predescu A.M.,Polytechnic University of Bucharest | Predescu A.,Polytechnic University of Bucharest | Vasile E.,METAV CD | Predescu C.,Polytechnic University of Bucharest
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2011

The paper refers at synthesis preparation of some iron oxides useful in different industrial applications, with high capacities of adsorption for different metal ions from wastewaters. The synthesis method was partial reduction coprecipitation for Fe3O4 nanoparticles, followed by aeration of acidified magnetite nanoparticles for obtaining the γ-Fe2O3 nanoparticles, and also a mechanical alloying in order to obtain a nanoscale compound, copper ferrite (CuFe2O4). In order to validate the obtained compounds the investigation methods were scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction (XRD) techniques. The stability of the nanomaterials, after 24 hours, was tested and measured with atomic absorption spectrometry (AAS).

Matei E.,Polytechnic University of Bucharest | Predescu C.,Polytechnic University of Bucharest | Berbecaru A.,Polytechnic University of Bucharest | Predescu A.,Polytechnic University of Bucharest | TrusCAa R.,METAV CD
Digest Journal of Nanomaterials and Biostructures | Year: 2011

Two different protocols for magnetite and magnetite covered with dextran are presented. These products can be used in waste water treatment, especially as adsorbents for different metal ions. The synthesis methods, characterization of the final products and leaching test at different pH media were tested. The investigation methods for the characterization of the products obtained with different methods were scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The quantity of iron dissolved from magnetite was evaluated with flame atomic absorption spectrometry (FAAS).

Matei E.,Polytechnic University of Bucharest | Predescu A.,Polytechnic University of Bucharest | Vasile E.,METAV CD
Journal of Physics: Conference Series | Year: 2011

The paper describes the properties of some nanopowders obtained by coprecipitation and used as adsorbent for wastewater treatment. The Fe 3O4 and γ-Fe2O3 nanopowders were obtained using iron salts and NaOH as precipitation agents. D-sorbitol was used to prevent the agglomeration between the nanoparticles. The particle size and distribution were detected using a transmission electron microscopy (TEM) and a scanning electron microscope (SEM) equipped with dispersive analyze system in X radiation energy (EDS). The structure of the iron oxide nanoparticles was characterized by X-ray powder diffraction. Thus, the nanoparticles were characterized and compare in terms of particle size and chemical composition and used for adsorption studies in order to removal hexavalent chromium from waste waters.

Taca M.,Metav CD | Constantinescu D.M.,Polytechnic University of Bucharest | Baciu F.,Polytechnic University of Bucharest | Geanta V.,Polytechnic University of Bucharest | And 2 more authors.
Materials Today: Proceedings | Year: 2016

Microalloyed (MA) steels are suitable as a replacement for plain carbon steels grades due to their ability to achieve final engineering properties in as forged and normalized condition, thus eliminating the need for subsequent heat treatments. Compared to the quenched and tempered steels at the same hardness, MA steels have much lower toughness so their further use is restricted to parts not subjected to impact loadings. The study on the influence of forging and cooling parameters in obtaining high toughness microalloyed steels within specified compositional domains is presented in the paper. The results of the experiments will be used for the development of a new microllaoyed steel with improved toughness and formability as a replacement for low alloyed heat treatable steels. © 2016 Elsevier Ltd.

Sima M.,National Institute of Materials Physics Bucharest | Vasile E.,METAV CD
Materials Research Bulletin | Year: 2013

In this work, ZnO films, nanorod and nanorod/shell arrays were synthesized on the surface of PET-ITO electrodes by electrochemical methods. ZnO films with high optical transmittance were prepared from a zinc nitrate solution using a pulsed current technique with a reduced pulse time (3 s). The X-ray diffraction pattern of ZnO film deposited on PET-ITO electrode showed that it has a polycrystalline structure with preferred orientations in the directions [0 0 2] and [1 0 3]. ZnO nanorods were synthesized on electrochemical seeded substrate in an aqueous solution containing zinc nitrate and hexamethylenetetramine. In order to increase the stability of PET-ITO electrode to electrochemical and chemical stresses during ZnO nanorods deposition the surface of the electrode was treated with a 17 wt% NH4F aqueous solution. Electrochemical stability of PET-ITO electrode was evaluated in a solution containing nitrate ions and hexamethylenetetramine. ZnO nanorod/shell arrays were fabricated using eosin Y as nanostructuring agent. Photoluminescence spectra of ZnO nanorod and ZnO nanorod/shell arrays prepared on the surface of PET-ITO electrode were discussed comparatively. By employing the 1.5 μm-length ZnO nanorod/shell array covered with a Cu2O film a photovoltaic device was fabricated on the PET-ITO substrate. © 2012 Elsevier Ltd.

Sima M.,National Institute of Materials Physics Bucharest | Vasile E.,METAV CD
Thin Solid Films | Year: 2012

An array of ZnO nanorods, each nanorod being covered with a shell of porous ZnO was prepared in two steps by hydrothermal-electrochemical processes. The growth of ZnO nanorods was achieved in a zinc nitrate and hexamethylenetetramine aqueous solution on fluorine-doped tin oxide film. The porous ZnO shell was grown from a similar solution in the presence of eosin Y as nanostructuring agent. A dye-sensitized solar cell was assembled using as photoanode an eosin Y sensitized ZnO nanorod/shell layer. © 2011 Elsevier B.V. All rights reserved.

Oprea O.,Polytechnic University of Bucharest | Ciocirlan O.,Polytechnic University of Bucharest | Badanoiu A.,Polytechnic University of Bucharest | Vasile E.,METAV CD
Central European Journal of Chemistry | Year: 2014

ZnO nanoparticles were synthesized in mixtures of ionic liquids based on imidazolium cation with organic solvents (dimethyl sulfoxide and ethylene glycol) by a simple, one-step solution route at low temperature. The effect of these mixtures on the morphology, size and properties of as obtained ZnO nanopowders was investigated. The obtained nanopowders have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy (UV-Vis) and photoluminescence (PL). The effect of the ionic liquid mixture on the photocatalytic degradation of methylene blue has been analysed. The XRD studies confirmed the hexagonal wurtzite structure of the obtained ZnO powder. The UV-Vis absorption spectra present the typical shape for ZnO, with a broad band situated in the UV region, with the maximum around 360 nm. The calculated band-gap energy is in interval 3.25-3.28 eV. The synthesized ZnO nanopowders have high photocatalytic activity against methylene blue, the best results being obtained when 1-ethyl-3-methylimidazolium tetrafluoroborate was used as the solvent. [Figure not available: see fulltext.] © 2014 Versita Warsaw and Springer-Verlag Wien.

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