Zirconium-Modified Medium-Entropy Alloy (TiVNb)85Cr15 for Hydrogen Storage.

In this study, we investigate the effect of small amounts of zirconium alloying the medium-entropy alloy (TiVNb)85Cr15, a promising material for hydrogen storage. Alloys with 1, 4, and 7 at.% of Zr were prepared by arc melting and found to be multiphase, comprising at least three phases, indicating that Zr addition does not stabilize a single-phase solid solution. The dominant BCC phase (HEA1) is the primary hydrogen absorber, while the minor phases HEA2 and HEA3 play a crucial role in hydrogen absorption/desorption. Among the studied alloys, Zr4 (TiVNb)81Cr15Zr4 shows the highest hydrogen storage capacity, ease of activation, and reversibly retrievable hydrogen. This alloy can absorb hydrogen at room temperature without additional processing, with a reversible capacity of up to 0.74 wt.%, corresponding to hydrogen-to-metal ratio H/M = 0.46. The study emphasizes the significant role of minor elemental additions in alloy properties, stressing the importance of tailored compositions for hydrogen storage applications. It suggests a direction for further research in metal hydride alloys for effective and safe hydrogen storage.

The Influence of Manganese Addition on the Properties of Biodegradable Zinc-Manganese-Calcium Alloys.

This study focuses on the preparation and characterization of zinc-based alloys containing magnesium, calcium, and manganese. The alloys were prepared by the melting of pure elements, casting them into graphite molds, and thermo-mechanically treating them via hot extrusion. The phase compositions of the samples were analyzed using X-ray diffraction technique and SEM/EDX analysis. The analysis confirmed that in addition to the Zn matrix, the materials are reinforced by the CaZn13, MgZn2, and Mn-based precipitates. The mechanical properties of the alloys were ascertained by tensile, compressive, and bending tests, measurement of the samples microhardness and elastic modulus. The results indicate that an increase in Mn content leads to an increase in the maximum stress experienced under both tension and compression. However, the plastic deformation of the alloys decreases with increasing Mn content. This study provides valuable insights into the microstructural changes and mechanical behavior of zinc-based alloys containing magnesium, calcium, and manganese, which can be used to design alloys for specific biomedical applications.

Structure and Physical Properties of Mg93-xZnxCa7 Metallic Glasses.

The Mg-Zn-Ca system has previously been proposed as the most suitable biodegradable candidate for biomedical applications. In this work, a series of ribbon specimens was fabricated using a melt-spinning technique to explore the glass-forming ability of the Mg-Zn-Ca system along the concentration line of 7 at.% of calcium. A glassy state is confirmed for Mg50Zn43Ca7, Mg60Zn33Ca7, and Mg70Zn23Ca7. Those samples were characterised by standard methods to determine their mass density, hardness, elastic modulus, and crystallisation temperatures during devitrification. Their amorphous structure is described by means of pair distribution functions obtained by high-energy X-ray and neutron diffraction (HEXRD and ND) measurements performed at large-scale facilities. The contributions of pairs Mg-Mg, Mg-Zn, and Zn-Zn were identified. In addition, a transformation process from an amorphous to crystalline structure is followed in situ by HEXRD for Mg60Zn33Ca7 and Mg50Zn43Ca7. Intermetallic compounds IM1 and IM3 and hcp-Mg phase are proposed to be formed in multiple crystallisation eventss.

The Impact of Redox, Hydrolysis and Dehydration Chemistry on the Structural and Magnetic Properties of Magnetoferritin Prepared in Variable Thermal Conditions.

Ferritin, a spherically shaped protein complex, is responsible for iron storage in bacteria, plants, animals, and humans. Various ferritin iron core compositions in organisms are associated with specific living requirements, health state, and different biochemical roles of ferritin isomers. Magnetoferritin, a synthetic ferritin derivative, serves as an artificial model system of unusual iron phase structures found in humans. We present the results of a complex structural study of magnetoferritins prepared by controlled in vitro synthesis. Using various complementary methods, it was observed that manipulation of the synthesis technology can improve the physicochemical parameters of the system, which is useful in applications. Thus, a higher synthesis temperature leads to an increase in magnetization due to the formation of the magnetite phase. An increase in the iron loading factor has a more pronounced impact on the protein shell structure in comparison with the pH of the aqueous medium. On the other hand, a higher loading factor at physiological temperature enhances the formation of an amorphous phase instead of magnetite crystallization. It was confirmed that the iron-overloading effect alone (observed during pathological events) cannot contribute to the formation of magnetite.

Characterization of megahertz X-ray laser beams by multishot desorption imprints in PMMA.

Proper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz (MHz) repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5-nm beam generated by the free-electron laser in Hamburg (FLASH) using the method of multi-pulse desorption imprints in poly(methyl methacrylate)(PMMA). The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single-shot ablation imprints and multi-shot desorption imprints at both low (10 Hz) and high (1 MHz) repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function model.

Mechanism of single-shot damage of Ru thin films irradiated by femtosecond extreme UV free-electron laser.

Ruthenium is a perspective material to be used for XUV mirrors at free-electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser-matter interaction. In this work, we present single-shot damage studies of thin Ru films irradiated by femtosecond XUV free-electron laser pulses at FLASH. Ex-situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte-Carlo code XCASCADE(3D) and the two-temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologies.

Experimental study of EUV mirror radiation damage resistance under long-term free-electron laser exposures below the single-shot damage threshold.

The durability of grazing- and normal-incidence optical coatings has been experimentally assessed under free-electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10% of the single-shot damage threshold. The experiment was performed at FLASH, the Free-electron LASer in Hamburg, using 13.5 nm extreme UV (EUV) radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20° and 10° grazing incidence, respectively. Mo/Si periodical multilayer structures were tested in the Bragg reflection condition at 16° off-normal angle of incidence. The exposed areas were analysed post-mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X-ray photoelectron spectroscopy. The analysis revealed that Ru and Mo/Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV-induced oxidation of the surface.

Role of heat accumulation in the multi-shot damage of silicon irradiated with femtosecond XUV pulses at a 1 MHz repetition rate.

The role played by heat accumulation in multi-shot damage of silicon was studied. Bulk silicon samples were exposed to intense XUV monochromatic radiation of a 13.5 nm wavelength in a series of 400 femtosecond pulses, repeated with a 1 MHz rate (pulse trains) at the FLASH facility in Hamburg. The observed surface morphological and structural modifications are formed as a result of sample surface melting. Modifications are threshold dependent on the mean fluence of the incident pulse train, with all threshold values in the range of approximately 36-40 mJ/cm2. Experimental data is supported by a theoretical model described by the heat diffusion equation. The threshold for reaching the melting temperature (45 mJ/cm2) and liquid state (54 mJ/cm2), estimated from this model, is in accordance with experimental values within measurement error. The model indicates a significant role of heat accumulation in surface modification processes.

Investigating the interaction of x-ray free electron laser radiation with grating structure.

The interaction of free electron laser pulses with grating structure is investigated using 4.6±0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7±8.7 mJ/cm2, the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold.

How metallic Fe controls the composition of its native oxide.

We have studied in situ the oxidation of ultrathin iron layers and monitored the chemical changes induced by subsequent deposition of Fe metal using hard x-ray absorption spectroscopy. The site sensitivity of the technique allows us to quantify the composition of the layer throughout the oxidation or deposition process. It is found that the thin native oxide incorporates a significant fraction of Fe atoms remaining in a metallic configuration even in the saturated state. Subsequent deposition of Fe leads to a complete reduction of the oxide that adopts an FeO-like structure containing Fe2+ sites only.

Atomic structure of Al(89)La(6)Ni(5) metallic glass.

Atomic structures of amorphous Al(89)La(6)Ni(5), prepared by single-roller melt spinning, and pre-annealed at 493 and 588 K for 1 h, were characterized by differential scanning calorimetry, x-ray diffraction with a large wavevector transfer value, La L(3)-edge and Ni K-edge x-ray absorption fine structure and the reverse Monte Carlo technique. In the as-prepared amorphous alloy, our study reveals that the Ni-Al distance is 2.38 ± 0.02 Å coupled with a coordination number as low as 6.2. The Al-Al distance was found to be ∼4.5% shorter than the nominal atomic diameter of aluminium and the coordination number to be ∼39% less than expected from the dense random packing model. Crystallization of the Al(89)La(6)Ni(5) glassy alloy at high temperatures can be described as follows: [amorphous alloy] [Formula: see text] [fcc-Al] + [bcc-(AlLa)] + residual amorphous [Formula: see text] [fcc-Al] + [o-Al(3)Ni ] + [o-La(3)Al(11) ].