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Corneliu S. Stan,Marcel Popa,Daniel Sutiman,Petronela Horlescu 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.4
Large transparent photoluminescent monoliths were prepared by embedding newly synthesized Eu(III), Tb(III) and Y(III) complexes with 2-(1H-1,2,4-Triazol-3-yl)pyridine ligand in silica matrices through a modified sol-gel process. The remarkable luminescent properties of the free complexes were preserved in silica matrix, resulting in red, green and blue monoliths with a shape that may be tailored during the gelation process according to specific applications. Prior to embedment, the complexes prepared at 1/3 metal to ligand ratio were investigated through elemental analysis, thermal analysis, FT-IR, mass and fluorescence spectroscopy while the obtained silica monoliths were supplementary investigated through SEM and fluorescence spectroscopy. The emission peaks are located at 612 nm for the monolithic silica embedded Eu(III) complex, at 542 nm for the monolithic silica embedded Tb(III) complex and at 482 nm respectively for the silica monolith containing the Y(III) complex. Their excellent photoluminescent properties may recommend them as photonic conversion materials in various optoelectronic applications.
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Surface Protection Obtained by Anodic Oxidation of New Ti-Ta-Zr Alloy
( C. Vasilescu ),( S. I. Drob ),( J. M. Calderon Moreno ),( P. Drob,M. Popa ),( E. Vasilescu ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.2
A new 80Ti-15Ta-5Zr wt% alloy surface was protected by anodic oxidation in phosphoric acid solution. The protective oxide layer (TiO<sub>2</sub>, ZrO<sub>2</sub> and Ta suboxides and thickness of 15.5 nm) incorporated PO<sub>4</sub> <sup>3-</sup> ions from the solution, according to high resolution XPS spectra. The AFM analysis determined a high roughness with SEM detected pores (20 - 50 nm). The electrochemical studies of bare and anodically oxidized Ti-15Ta-5Zr alloy in Carter-Brugirard saliva of different pH values and saliva with 0.05M NaF, pointed to a nobler surface for the protected alloy, with a thicker electrodeposited oxide layer acting as a barrier against aggressive ions. The oxidized alloy significantly decreased corrosion current densities and total quantity of ions released into the oral environment in comparison with the bare one, at higher polarisation resistance and protective capacity of the electrodeposited layer. The impedance data revealed a bi-layered oxidation film formed by: a dense, compact, barrier layer in contact with the metallic substrate, decreasing the potential gradient across the metal/oxide layer/solution interface, reducing the anodic dissolution and a more permissive, porous layer in contact with the electrolyte. The open circuit potential for protected alloy shifted to nobler values, with thickening of the oxidation film signifying long-term protection.
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Hirian R.,Bortnic R.,Popa F.,Gutoiu S.,Benea D.,Souca G.,Pop V. 한국물리학회 2023 Current Applied Physics Vol.51 No.-
Magnetic filaments for fused deposition modeling, 3d printing, were produced by depositing Nylon12 onto SmCo5/Fe exchange coupled nanocomposites powders by liquid-liquid phase separation and precipitation. The produced filaments have a high coercive filed of 1 T at 300 K. The usefulness of these types of filaments in the production of 3D printed magnets with special stray field geometries was investigated by implementing an evolutionary algorithm capable of generating the appropriately shaped magnet. The desired, calculated and magnet stray field geometries were compared and found to be reasonably similar.
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B4C in ex-situ spark plasma sintered MgB2
M. Burdusel,G. Aldica,S. Popa,M. Enculescu,V. Mihalache,A. Kuncser,I. Pasuk,P. Badica 한국물리학회 2015 Current Applied Physics Vol.15 No.10
Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C)x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 ℃ for 3 min. The average particle size of B4C raw powder was relatively high of 4 mm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density Jc at high magnetic fields and of the irreversibility field Hirr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a Jc of 100 A/cm2 is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions.
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( J. M. Calderon Moreno ),( P. Drob ),( C. Vasilescu ),( S. I. Drob ),( M. Popa ),( E. Vasilescu ) 한국부식방식학회 2017 Corrosion Science and Technology Vol.16 No.5
Film of new Ti-15Zr-5Nb alloy formed during galvanic anodizing in orthophosphoric acid solution was characterized by optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman micro-spectroscopy. Its anticorrosive properties were determined by electrochemical techniques. The film had a layer with nanotube-like porosity with diameters in 500-1000 nm range. The nano layer contained significant amounts of P and O as well as alloying element. Additionally, Raman micro-spectroscopy identified oxygen as oxygen ion in TiO<sub>2</sub> anatase and phosphorous as P<sub>2</sub>O<sub>7</sub><sup>4-</sup> ion in phosphotitanate compound. All potentiodynamic polarization curves in artificial Carter-Brugirard saliva with pH values (pH= 3.96, 7.84, and 9.11) depending on the addition of 0.05M NaF revealed nobler behavior of anodized alloy and higher polarization resistance indicating the film is thicker and more compact nanolayer. Lower corrosion rates of the anodized alloy reduced toxicity due to less released ions into saliva. Bigger curvature radii in Nyquist plot and higher phase angle in Bode plot for the anodized alloy ascertain a thicker, more protective, insulating nanolayer existing on the anodized alloy. Additionally, ESI results indicate anodized film consists of an inner, compact, barrier, layer and an outer, less protective, porous layer.
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