National Institute Of Materials Physics - Romania

A testing methodology and a new "anchor"geometry for tensile samples were developed for evaluation of the W/Cu joint strength between the W monoblock and the CuCrZr cooling pipe joined via the Cu interlayer in the ITER-specification monoblock. The proposed samples can be machined from the ITER-specification monoblock. These monoblock tensile samples are designed for uniaxial tests allowing their remote manipulation for testing in hot cells after neutron irradiation, which is crucial for the assessment of the effect of this irradiation. For validation purposes, tensile tests with standard miniaturised dog-bone samples were performed using prototype block-to-block joints (W/CuCrZr) produced with the field-assisted sintering technique. The results are obtained from the conventional and the new tensile samples. Conventional samples were machined from the W/CuCrZr block-to-block joints, while the new "anchor"tensile samples were machined from the W/CuCrZr block-toblock joints and ITER monoblock containing the W block and Cu interlayer. A good agreement in the evaluation of the joint strength was obtained. The fracture surfaces and the joint interface were investigated with scanning electron microscopy. Micro-hardness was characterised across the joint interface.

Currently, the treatment of wounds is still a challenge for healthcare professionals due to high complication incidences and social impacts, and the development of biocompatible and efficient medicines remains a goal. In this regard, mesoporous materials loaded with bioactive compounds from natural extracts have a high potential for wound treatment due to their nontoxicity, high loading capacity and slow drug release. MCM-41-type mesoporous material was synthesized by using sodium trisilicate as a silica source at room temperature and normal pressure. The synthesized mesoporous silica was characterized by using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), N2 absorption-desorption (BET), Dynamic Light Scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR), revealing a high surface area (BET, 1244 m2/g); pore diameter of approx. 2 nm; and a homogenous, ordered and hexagonal geometry (TEM images). Qualitative monitoring of the desorption degree of the Salvia officinalis (SO) extract, rich in ursolic acid and oleanolic acid, and Calendula officinalis (CO) extract, rich in polyphenols and flavones, was performed via the continuous recording of the UV-VIS spectra at predetermined intervals. The active ingredients in the new composite MCM-41/sage and marigold (MCM-41/SO & CO) were quantified by using HPLC-DAD and LC-MS-MS techniques. The evaluation of the biological composites' activity on the wound site was performed on two cell lines, HS27 and HaCaT, naturally involved in tissue-regeneration processes. The experimental results revealed the ability to stimulate collagen biosynthesis, the enzymatic activity of the main metalloproteinases (MMP-2 and MMP-9) involved in tissue remodeling processes and the migration rate in the wound site, thus providing insights into the re-epithelializing properties of mesoporous composites.

A convenient and low-cost sol-gel approach for the one-step synthesis of ZnO-P2O5-rGO nanostructures with tuned bandgap and fluorescence was investigated. The obtained hybrid nanostructures exploit the properties of zinc oxide, graphene oxide and phosphorous oxide as promising candidates for a wide range of optoelectronic applications. A predominant amorphous structure, ZnO-P2O5-rGO, containing ZnO nanorods was evidenced by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The estimated size of the ZnO nanorods in nanostructures with P2O5 was noticed to decrease when the P2O5/ZnO ratio was increased. The presence of ZnO, P2O5 and rGO was confirmed by Fourier-transform infrared spectroscopy (FTIR) and Raman investigation. P2O5 was noticed to tune the bandgap and the fluorescence emissions of the nanostructured films, as estimated by UV-Vis-NIR and fluorescence spectroscopy, respectively. The electrical measurements performed at room temperature showed that the main influence on the film's resistivity does not come from the 1% rGO doping but from the P2O5/ZnO ratio. It was found that a 10/90 molar ratio of P2O5/ZnO decreases the resistivity almost seven-fold compared with rGO-doped ZnO films.

Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001---0.01) were produced by a sol-gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1-1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and Fe-57 Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1-1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1-1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.

Microemulsions are nanocolloidal systems composed of water, an oil, and a surfactant, sometimes with an additional co-surfactant, which have found a wide range of practical applications, including the extractive removal of contaminants from polluted water. In this study, microemulsion systems, including a nonionic surfactant (Brij 30), water, and esters selected from two homologous series of C-1-C-6 alkyl acetates and ethyl C-1-C-4 carboxylates, respectively, were prepared by the surfactant titration method. Phase transitions leading to the formation of Winsor II and Winsor IV microemulsions were observed and phase diagrams were constructed. The dependences of phase transitions on the salinity and pH and the addition of isopropanol as a co-surfactant were also investigated. Some physical properties, namely density, refractive index, electrical conductivity, dynamic viscosity, and particle size, were measured for a selection of Winsor IV microemulsions, providing further insight into some other phase transitions occurring in the monophasic domains of phase diagrams. Finally, Winsor II microemulsions were tested as extraction solvents for the removal of four tricyclic antidepressant drugs from aqueous media. Propyl acetate/Brij 30/H2O microemulsions provided the best extraction yields (>90%), the highest Nernst distribution coefficients (similar to 40-88), and a large volumetric ratio of almost 3 between the recovered purified water and the resulting microemulsion extract. Increasing the ionic strength (salinity) or the pH of the aqueous antidepressant solutions led to an improvement in extraction efficiencies, approaching 100%. These results could be extrapolated to other classes of pharmaceutical contaminants and suggest ester- and nonionic surfactant-based microemulsions are a promising tool for environmental remediation.

We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers-the first regime of no interlayer F-F* coupling. F-F* coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in structures with 6.0-9.0-nm-thick FeMn spacers, the interlayer coupling exists only in a finite temperature interval just below the effective Neel temperature of the spacer, which is due to magnon-mediated exchange through the thermally softened antiferromagnetic spacer, vanishing at lower temperatures. The third regime, with FeMn thinner than 4 nm, is characterized by a much stronger interlayer coupling in the entire temperature interval, which is attributed to a magnetic-proximity induced ferromagnetic exchange. These experimental results, spanning the key geometrical parameters and thermal regimes of the F*/AF/F nanostructure, complemented by a comprehensive theoretical analysis, should broaden the understanding of the interlayer exchange in magnetic multilayers and potentially be useful for applications in spin thermionics.

Calcium borohydride (Ca(BH4)(2)) is a complex hydride that has been less investigated compared to its lighter counterpart, magnesium borohydride. While offering slightly lower hydrogen storage capacity (11.5 wt% theoretical maximum, 9.6 wt% under actual dehydrogenation conditions), there are many improvement avenues for maximizing the reversible hydrogen storage that have been explored recently, from DFT calculations and polymorph investigations to reactive hydride composites (RHCs) and catalytic and nanosizing effects. The stability of Ca(BH4)(2), the possibility of regeneration from spent products, and the relatively mild dehydrogenation conditions make calcium borohydride an attractive compound for hydrogen storage purposes. The ionic conductivity enhancements brought about by the rich speciation of borohydride anions can extend the use of Ca(BH4)(2) to battery applications, considering the abundance of Ca relative to alkali metal borohydrides typically used for this purpose. The current work aims to review the synthetic strategies, structural considerations of various polymorphs and adducts, and hydrogen storage capacity of composites based on calcium borohydrides and related complex hydrides (mixed anions, mixed cations, additives, catalysts, etc.). Additional applications related to batteries, organic and organometallic chemistry, and catalysis have been briefly described.

Calcium borohydride (Ca(BH4)(2)) is a complex hydride that has been less investigated compared to its lighter counterpart, magnesium borohydride. While offering slightly lower hydrogen storage capacity (11.5 wt% theoretical maximum, 9.6 wt% under actual dehydrogenation conditions), there are many improvement avenues for maximizing the reversible hydrogen storage that have been explored recently, from DFT calculations and polymorph investigations to reactive hydride composites (RHCs) and catalytic and nanosizing effects. The stability of Ca(BH4)(2), the possibility of regeneration from spent products, and the relatively mild dehydrogenation conditions make calcium borohydride an attractive compound for hydrogen storage purposes. The ionic conductivity enhancements brought about by the rich speciation of borohydride anions can extend the use of Ca(BH4)(2) to battery applications, considering the abundance of Ca relative to alkali metal borohydrides typically used for this purpose. The current work aims to review the synthetic strategies, structural considerations of various polymorphs and adducts, and hydrogen storage capacity of composites based on calcium borohydrides and related complex hydrides (mixed anions, mixed cations, additives, catalysts, etc.). Additional applications related to batteries, organic and organometallic chemistry, and catalysis have been briefly described.

Energy production, distribution, and storage remain paramount to a variety of applications that reflect on our daily lives, from renewable energy systems, to electric vehicles and consumer electronics. Hydrogen is the sole element promising high energy, emission-free, and sustainable energy, and metal hydrides in particular have been investigated as promising materials for this purpose. While offering the highest gravimetric and volumetric hydrogen storage capacity of all known materials, metal hydrides are plagued by some serious deficiencies, such as poor kinetics, high activation energies that lead to high operating temperatures, poor recyclability, and/or stability, while environmental considerations related to the treatment of end-of-life fuel disposal are also of concern. A strategy to overcome these limitations is offered by nanotechnology, namely embedding reactive hydride compounds in nanosized supports such as graphene. Graphene is a 2D carbon material featuring unique mechanical, thermal, and electronic properties, which all recommend its use as the support for metal hydrides. With its high surface area, excellent mechanical strength, and thermal conductivity parameters, graphene can serve as the support for simple and complex hydrides as well as RHC (reactive hydride composites), producing nanocomposites with very attractive hydrogen storage properties.

The Cu-Y2O3 and CuCrZr-Y2O3 materials have been devised as thermal barriers in nuclear fusion reactors. It is expected that in the nuclear environments, the materials should be working on extreme conditions of irradiation. In this work the Cu-Y2O3 and CuCrZr-Y2O3 were prepared and then irradiated in order to understand the surface irradiation resistance of the material. The composites were prepared in a glove box and consolidated with spark plasma sintering. The microstructures revealed regions of Y2O3 dispersion and Y2O3 agglomerates both in the Cu matrix and in the CuCrZr. The irradiated samples did not show any surface modification indicating that the materials seem to be irradiation resistant in the present situation. The thermal conductivity values for all the samples measured are lower than pure Cu and higher than pure W, however are higher than those expected, and therefore, the application of these materials as thermal barriers is compromised.