National Institute Of Materials Physics - Romania

The influence of waste glass and red mud addition as alternative source of aluminosilicate precursors on the microstructural, mechanical, and leaching properties of bottom ash-based geopolymer was studied in this work through mineralogical, morphological, and spectroscopic analysis, as well as by conducting compressive strength and leaching tests. The bottom ash-based geopolymer composites were synthesized by adding a constant amount of waste glass (10% by weight) and increasing amounts of red mud (up to 30% by weight). The results derived from FTIR, Si-29 and Al-27 MAS NMR, and SEM-EDX revealed that adding up to 10% (by weight) red mud to the synthesis mixes leads to an increase in the degree of geopolymerization of the activated mixes. The compressive strength followed the same trend. An increase of more than 10% (by weight) red mud added to the synthesis mixes results in a significant decrease of compressive strength of the geopolymer composites. A low leachability of geopolymer composites in regard with their contaminants was revealed especially for those with good compressive strength.

Sn nanoparticles (NPs) are usually obtained by difficult chemical routes in several steps followed by thermal treatments. Here, a simple and clean method, to obtain Sn NPs directly on the substrate, is developed based on a vapor transport technique. The method is versatile, thus can be easily adjusted to obtain Sn NPs of different size, areal density and morphology, by controlling the deposition conditions. NPs are grown on Si/SiO2 substrate and characterized. Water contact angle measurements show that Sn nanoparticles increase the surface hydrophobicity by 20%. Thus, NPs cleanly obtained from a low-cost, earth-abundant, and environmentally friendly material, can be used to modulate the wettability of surfaces. (C) 2020 Elsevier B.V. All rights reserved.

Mononuclear Mn(II) coordination compound, [Mn(H2L)Cl-2] (1), was synthesized by the reaction of H2L and MnCl2 center dot 4H(2)O in methanol where H2L is tridentate ONO-donor hydrazone ligand [H2L = (E)-N'-(2-hydroxy-5-iodobenzylidene)isonicotinohydrazide]. The reaction of H2L with MnCl2 center dot 4H(2)O in the presence of excess amount of NaN3 in methanol gave an azido bridged dinuclear Mn(III) coordination compound, [Mn-2(L)(mu-N-3)(2)(CH3OH)(2)] (2), whereas in the presence of low amount of NaN3, a phenolate bridged dinuclear Mn(II) coordination compound, [Mn-2(HL)(2)(CH3OH)(2)Cl-2]center dot CH3OH (3), was obtained. These compounds were characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements. The structural studies indicated that the ligand is coordinated as ONO-donor ligand in 1-3 and behave as a neutral, dianionic and monoanionic ligand in compounds 1, 2 and 3, respectively. There is a good agreement between spectroscopic properties and structures of the compounds. Several synthetic attempts indicated that the azide anion has considerable effect on the formation of phenolate bridged dinuclear Mn(II) coordination compound which attributed to its general basic properties. Magnetic measurements indicate the formation of dinuclear molecules with ferromagnetic intramolecular couplings in the case of 2 and 3 as well as with much weaker and distributed antiferromagnetic interactions among the dinuclear units of these compounds. (C) 2020 Elsevier Ltd. All rights reserved.

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs(R)BG alkali-free SBG system (mol%: SiO2-38.49, CaO-36.07, P2O5-5.61, MgO-19.24, CaF2-0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (similar to 600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (R-RMS < 1 nm) and hydrophilic (water contact angle of similar to 65 degrees). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs(R)BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of similar to 53 MPa, Lc3 critical load value of similar to 4.9 N, hardness of similar to 6.1 GPa and an elastic modulus of similar to 127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays.

Almost six decades ago, in Romania a small group of physicists begun to study chalcogenide compositions, motivated primarily by the desire to understand the phase-change phenomenon in these materials, discovered recently, at that time, by Stanford R. Ovshinsky. It took not too long for them to realize the challenges these materials set to the research. With newcomers to the field, the research was broadened. In some cases just for basic research, to model, and to understand the chalcogenide materials, whereas in other cases, the applicative potential was revealed and used. Herein, the evolution of the field of these somewhat exotic materials is followed, listing the main contributions done in Romania, both in basic and applied research.

The second magnetization peak (SMP) in the fourfold symmetric superconducting single crystals (such as iron pnictides and tetragonal cuprates) has been attributed to the rhombic-to-square transition (RST) of the quasi-ordered vortex solid (the Bragg vortex glass, BVG). This represents an alternative to the pinning-induced BVG disordering as the actual SMP mechanism. The analysis of the magnetic response of BaFe2(As1-xPx)(2) specimens presented here shows that the SMP is not generated by the RST. However, the latter can affect the pinning-dependent SMP onset field if this is close to the (intrinsic) RST line, through the occurrence of a "shoulder" on the magnetic hysteresis curves m(H), and a maximum in the temperature variation of the DC critical current density. These features disappear in AC conditions, where the vortex system is dynamically ordered in the RST domain, emphasizing the essential role of vortex dislocations for an efficient accommodation of the vortex system to the pinning landscape and the SMP development. The m(H) shoulder is associated with a precipitous pinning-induced proliferation of dislocations at the RST, where the BVG elastic "squash" modulus softens. The DC magnetization relaxation indicates that the pinning-induced vortex system disordering continues above the RST domain, as the basic SMP mechanism.

Structural and magnetic properties of Fe oxide nanoparticles prepared by laser pyrolysis and annealed in high pressure hydrogen atmosphere were investigated. The annealing treatments were performed at 200 degrees C (sample A200C) and 300 degrees C (sample A300C). The as prepared sample, A, consists of nanoparticles with similar to 4 nm mean particle size and contains C (similar to 11 at.%), Fe and O. The Fe/O ratio is between gamma-Fe2O3 and Fe3O4 stoichiometric ratios. A change in the oxidation state, crystallinity and particle size is evidenced for the nanoparticles in sample A200C. The Fe oxide nanoparticles are completely reduced in sample A300C to alpha-Fe single phase. The blocking temperature increases from 106 K in A to 110 K in A200C and above room temperature in A300C, where strong inter-particle interactions are evidenced. Magnetic parameters, of interest for applications, have been considerably varied by the specific hydrogenation treatments, in direct connection to the induced specific changes of particle size, crystallinity and phase composition. For the A and A200C samples, a field cooling dependent unidirectional anisotropy was observed especially at low temperatures, supporting the presence of nanoparticles with core-shell-like structures. Surprisingly high M-S values, almost 50% higher than for bulk metallic Fe, were evidenced in sample A300C.

Nanocrystalline PdO films have been characterized by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The results demonstrate that thermal oxidation in an O-2 atmosphere causes similar to 35-nm-thick nanocrystalline Pd films on SiO2/Si(100) substrates to undergo a sequence of phase transformations resulting in PdO formation, followed by PdO decomposition into metallic Pd atT > 1120 K. In the range 670-970 K, theaandctetragonal cell parameters of the nanocrystalline PdO films increase monotonically with increasing temperature. The present and previously reported data have been used to construct a model for the unit cell in the crystal structure of palladium(II) oxide. Based on the quasi-chemical approach, we propose a model that accounts for the observed increase in the tetragonal cell parameters and thep-type conductivity of the nanocrystalline PdO films in terms of the formation of excess interstitial oxygen atoms.

Titanium diffusion in tungsten is an undesirable phenomenon that may cause the drop of mechanical and thermal fatigue properties of tungsten base material and components in future fusion reactors. To avoid such as problematic, the effectiveness of two different diffusion coatings, deposited onto W base materials by means of RF magnetron sputtering (Cr and V layers), has been studied to analyze its impact on the operative brazing aspects of the W-Eurofer joints. Coatings with two different thicknesses were deposited over tungsten base material prepared using different surface roughness (0.08 and 0.09 mu m). The results indicated that Ti diffusion into tungsten base material after the brazing process was suppressed in all cases while the consecution of full metallic continuity was reached. However, both Cr and V layers were dissolved during the brazing process due to the high solubility of both elements into beta-Ti. Mechanical properties of the joints dropped especially when Cr is used but a strength higher than 100 MPa was obtained in the case of using V layers.