National Institute Of Materials Physics - Romania

Small multilayered laminated samples consisting of stacks of W (or K-doped W) foils without an interlayer or with interlayers from Cu, V, and Ti were exposed to a pulsed electron beam with an energy of 6 MeV in several irradiation sessions. All samples maintained their macroscopic integrity, suggesting that the W-metal laminate concept is compatible with high heat flux applications. The surface of the samples was analyzed using a scanning electron microscope (SEM) before and after each irradiation session. The experimental results indicate that electron beam irradiation induces obvious modifications on the surface of the samples. Morphological changes such as the appearance of nanodroplets, nanostructures, and melting and cracking, depending on the sample type and the electron beam fluence, are observed. The irradiation is carried out in a vacuum at a pressure of 2 to 4 x 10(-2) torr, without active cooling for the samples. The structures observed on the surface of the samples are likely due to electron beam heating and vaporization followed by vapor condensation in the volume adjacent to the surface.

This work reports on the influence of 5 MeV electron beam radiations on the morphological features and chemical structure of magnesium-doped hydroxyapatite/chitosan composite coatings generated by the magnetron sputtering technique. The exposure to ionizing radiation in a linear electron accelerator dedicated to medical use has been performed in a controllable manner by delivering up to 50 Gy radiation dose in fractions of 2 Gy radiation dose per 40 s. After the irradiation with electron beams, the surface of layers became nano-size structured. The partial detachment of irradiated layers from the substrates has been revealed only after visualizing their cross sections by scanning electron microscopy. The energy dispersive X-ray spectral analysis of layer cross-sections indicated that the distribution of chemical elements in the samples depends on the radiation dose. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction analysis have shown that the physicochemical processes induced by the ionizing radiation in the magnesium doped hydroxyapatite/chitosan composite coatings do not alter the apatite structure, and Mg remains bonded with the phosphate groups.

Bulk high density MgB2 and a composite material made of a PLA matrix and MgB2 powder inclusions were in vivo tested as candidates for biodegradable materials for orthopedic implants. A rat model was used. Implants were introduced into femoral bone, in transversal and longitudinal directions. Assessment of the implant-tissue interaction was performed by X-ray imaging, X-ray computer tomography, electron microscopy, cytology, and histopathology on samples at 40 and 90 days after surgery. Both materials are biocompatible, bone and adjacent soft tissue showing good tolerance of implants. Biodegradation of MgB2 is faster than for PLA-MgB2 composite, but in both cases, it is accompanied by bone regeneration. Results suggest that use of MgB2-containing composites can promote space and time control of degradation and promotes MgB2 as a promising material for fracture repair. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

Nano-nitride reinforcement of Fe-Cr alloys are under intense investigations, e.g., along with oxide-strengthened, nitride-strengthened reduced activation steels with superior high temperature mechanical properties are developed as materials for nuclear energy applications. Fe14Cr alloy powders were produced by mechanical milling for up to 170 h under a nitrogen atmosphere followed by heating under an Ar5%H-2 atmosphere to 600 degrees C-1120 degrees C. The samples were investigated by means of X-ray diffraction, DTA/TG and magnetic measurements. CrN, detected after milling for 58 h, reached 39 wt % (5.3 wt.% total N) at 170 h milling. The ferrite supersaturated with nitrogen shows a strong decrease in grain size and saturation magnetization, an increase in lattice constant, microstrain and coercivity, H-c. Upon heating, the metastable ultrafine alpha-ferrite and CrN in the as-milled samples undergo transformations and recrystallization into ferrite grains free of super-saturation, whose microstructure follows a continuous relaxation. The supersaturation with nitrogen was retained upon heating in the relatively stable ferrite crystalized at the milling stage. This microstructure undergoes a discontinuous relaxation in the 800 degrees C-1120 degrees C region: a pronounced decrease of grain size (down to similar to 25 nm), an increase of lattice constant, microstrain and H-c. These improvements were associated with features of discontinuous precipitation reaction of coherent nitride precipitates (involving a new alpha ''-phase with expanded lattice), in connection with the heating in the austenite phase field. Such microstructure refinement or (nitride) strengthening of Fe14Cr alloys can be achieved on powders milled for much less time as compared to previously reported (oxide dispersion) strengthening of Fe14Cr-W-Ti ferritic steels. (C) 2022 The Authors. Published by Elsevier B.V.

Exchange coupling in a SrFe12O19 - Fe3O4 nanocomposite magnet was explored in this study. The composition, microstructure, local structure and magnetic properties were investigated by XRD, SEM, Mossbauer spectroscopy, and SQUID magnetometry. The magnetoplumbite SrFe12O19 and spinel Fe3O4 structures were verified by X-ray diffraction. The morphology of the composite reveals the characteristics of the two components. The hyperfine parameters allowed the identification of the Wyckoff positions of the iron ions corresponding to the involved phases. The magnetic measurements of the composite, showing a single-phase-like magnetic hysteresis loop, confirmed the exchange coupling between the hard and soft magnetic phases.

The dielectric and electric properties of a core-shell SrFe12O19 - BNT-BT nanocomposite were explored in this study. The desired composition and the existence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. The dielectric constant values approached the case of BNT-BT due to the small amount of hexaferrite content. The electric properties were also derived.

NiTi cylindrical materials were obtained by spark plasma sintering at 850??C or 900??C from high purity Ni and Ti powders. These mixtures were previously processed by mechanical alloying for 8 and 15 hours. In order to increase the alloy homogeneity, the NiTi materials were subjected to post aging treatment in protective atmosphere at constant temperature 400??C and cooling in water with ice. All samples were characterized by optical microscopy, differential calorimetry (DSC), X-ray measurements (XRD) and micro/nanoindentation measurements. The results demonstrate that the NiTi materials obtained by this preparation route have good mechanical properties and can serve as a quantitative reference for the microstructure design of shape memory materials for various applications, such as the biomedical ones.

This paper describes for the first time two processing routes-the precursor method and the two-step wet chemical process-for the synthesis of magnetic cobalt ferrite using the Tamarindus indica fruit extract. These green approaches are eco-friendly, safe and efficient alternatives to classical chemical methods. The aqueous extract from tamarind fruit contains numerous metabolites (organic acids, aminoacids). All these bioactive components are able to chelate metal ions leading to the formation of the multimetallic complex (precursor of cobalt ferrite). The obtained precursor was characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, X-ray diffraction analysis (XRD) and magnetic measurements. The structure, morphology and magnetic behavior of the cobalt ferrite samples prepared through both synthesis routes were investigated by various characterization techniques: FTIR, XRD, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), Mossbauer spectroscopy and magnetic measurements. XRD data confirmed that a cubic spinel structure was obtained for both ferrite powders with average crystallite size of 13 and 5 nm, respectively. The microstructure study by SEM revealed the formation of nanocrystallites assemblies using the precursor method and carbon-rich particles forming granulated micron-sized agglomerates, embedding ferrite nanocrystallites obtained through the two-step wet chemical process. Mossbauer spectroscopy results evidenced relaxation processes in the CoFe2O4 samples at room temperature, and the main characteristics of the involved sublattices were derived. The magnetic investigation revealed a typical magnetic behavior for a spinel, with CoFe2O4 nanoparticles ferrimagnetic at low temperature and superparamagnetic at room temperature.

Nanoscale thermometers with high sensitivity are needed in domains which study quantum and classical effects at cryogenic temperatures. Here, we present a micrometer sized and nanometer thick chromium selenide cryogenic temperature sensor capable of measuring a large domain of cryogenic temperatures down to tenths of K. Hexagonal Cr-Se flakes were obtained by a simple physical vapor transport method and investigated using scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy measurements. The flakes were transferred onto Au contacts using a dry transfer method and resistivity measurements were performed in a temperature range from 7 K to 300 K. The collected data have been fitted by exponential functions. The excellent fit quality allowed for the further extrapolation of resistivity values down to tenths of K. It has been shown that the logarithmic sensitivity of the sensor computed over a large domain of cryogenic temperature is higher than the sensitivity of thermometers commonly used in industry and research. This study opens the way to produce Cr-Se sensors for classical and quantum cryogenic measurements.