No 9 (2023)

The biodistribution of Gd_0.5La_0.5F₃:Eu(15%) X-ray phosphor nanoparticles in the body and tissues of internal organs of balb/c laboratory mice was studied. Gd_0.5La_0.5F₃:Eu(15%) nanoparticles were obtained by the hydrothermal synthesis at 250°C for 24 h. Using X-ray powder diffraction, transmission electron microscopy, and dynamic light scattering, it was shown that a hexagonal phase was formed in the resulting sample, and the average size of nanoparticles varied in the range 30–40 nm. In vivo experiments have shown that intravenous administration of an aqueous solution of nanoparticles accumulates the sample mainly in the liver and spleen, with the maximum concentration being reached during the first day. According to the results of post-mortem analysis of tissues by micro-CT, it was shown that these nanoparticles formed conglomerates, their distribution over the volume of the organ was homogeneous. X-ray fluorescent analysis of liver and spleen tissue fragments allowed for elemental analysis and mapping. Distribution maps of heavy elements in the composition of nanoparticles (Gd, La, Eu) were similar to Fe distribution maps, which indicated the uniform distribution of Gd_0.5La_0.5F₃:Eu(15%) nanoparticles in the pulp of the internal tissues of the liver and spleen.

Corrosion resistance of zirconium-based amorphous alloys in simulating a biological fluid, as well as in aqueous solutions of hydrochloric acid (with HCl concentration 0.1, 0.2, 0.4 mol/L) was studied in this work. When studying the effect of simulating a biological fluid, the samples were exposed to the environment in two ways. In the first case, the sample was completely immersed in a corrosive liquid. In the second case, the sample was subjected to local action of a drop of biological fluid deposited on the surface. It has been established that prolonged exposure to the medium leads to the dissolution of the surface layer of the sample, while the local impact of drops practically does not affect the surface. Preliminary ion implantation of argon and nitrogen ions leads to a decrease in the effect of the biological fluid on the samples. Polarization curves are obtained for all investigated alloys. On the curves obtained during measurements on alloys in simulating a biological fluid, the cathode and anode branches have a standard form. It has been established that the polarization curves for zirconium-based alloys in an aqueous solutions (with HCl concentration 0.1, 0.2, 0.4 mol/l) depend on the elemental composition of the alloys. It has been established that in a sample without copper, the corrosion potential at different concentrations of HCl changes insignificantly. For a sample with a copper content of 15%, the corrosion potential shifts to the cathodic region with an increase in the concentration of hydrochloric acid. The polarization curves of the sample with a higher copper content of 45% are qualitatively different from the curves of the other samples. It is noted that, as in the previous sample, with an increase in the concentration of hydrochloric acid, the corrosion potential shifts to the negative region. It has been established that the corrosion resistance of amorphous alloys based on zirconium, which is the basis of the alloys under study, in the studied solutions increases in comparison with the crystalline one, which is due to the amorphous structure of the electrode material, which complicates the transition of the metal to the ionic state.

The sensitivity of the mechanical properties of materials to violations of the translational invariance of the crystal lattice makes it possible to manipulate these properties in the desired direction by doping or creating solid solutions. The paper theoretically studies the mechanisms of such manipulation in relation to materials in which the mobility of dislocations is controlled mainly by the potential relief of the crystal lattice – the so-called Peierls relief. Due to the concentration of alloying atoms in dislocation nuclei, which play the role of traps for these atoms, the dynamic properties of dislocations change, which also leads to modification of the macroscopic mechanical properties of the material. The theory of the effect of doping on the kink mechanism of overcoming the Peierls barriers is constructed taking into account the disordered content of solution atoms in dislocation nuclei. Correspondingly, the direct description of the kinetics of elementary processes characteristic of kinks has been replaced by a statistical description. The multidirectional effect of fluctuations in the solutes distribution, which increase the rate of formation of pairs of kinks, but inhibit the propagation of kinks along dislocation lines, is considered. Inhibition of kinks can lead to an anomalous nature of their mobility, so-called quasilocalisation. The conditions for the predominance of the accelerating or inhibiting factor corresponding in macroscopic terms to the hardening or softening of the material are found.

Layered composite materials Ti/Ta/Hf/ ceramic were produced via self-propagating high-temperature synthesis (SHS) of pre-structured samples using metal foils (Ti, Hf, Ta, Ni) and reaction tapes (Ti + 0.65C), (Ti + 1.7B) and (5Ti + 3Si). Reaction tapes were prepared by cold rolling from powder mixtures. The microstructure, elemental and phase compositions of the synthesized multilayer composite materials were characterized by Scanning Electron Microscopy (SEM) and X-ray analysis. Their flexural strength was determined according to the scheme of three-point loading at temperatures of 25 and 1100°С. The microstructure analysis of produced materials showed that the joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation and chemical reactions occurring in reaction tapes and on the surface of metal foils. The formation of thin intermediate layers in the form of cermets and eutectic solutions provides the synthesized multilayer materials with good strength properties (up to 275 MPa at 25°С, up to 72 MPa at 1100°С). These results are of interest for the development of construction materials operating under extreme conditions.

A method is proposed for determining the degree of collimation of a coherent X-ray beam using a planar multilens interferometer. The method is based on analyzing Talbot images, which are periodic patterns of interference fringes formed by the interferometer at appropriate distances. The high sensitivity of the position and period of the interference fringes to the shape of the X-ray beam wave front makes it possible to determine the degree of its collimation, as well as to evaluate the coherent properties of the radiation. The effectiveness of the proposed approach has been experimentally demonstrated at the ID15B beamline of the ESRF synchrotron radiation source. A theoretical study has been carried out, and the corresponding results of computer simulation have been presented. The experimentally data obtained fully correspond to the theoretical estimates.

Theoretical study of the phenomenon of superplasticity of metallic materials has been carried out. Numerical calculations were performed on the basis of a two-level finite element model of an elastoplastic medium. The plastic properties of the deformable medium element determining the deformation by uniaxial tension in superplasticity mode were found. It was shown that depending on the shape of the stress-strain curve (σ–ε) of the medium element, the various types of plastic flow localizations were observed at the macroscale level. The nonmonotonic dependence σ–ε of the deformable medium element having single maximum was determined as the condition for the appearance of a stable fracture neck. In the case when the dependence σ–ε characterized by the strengthening of the elementary volumes with two maxima, a propagating (running) neck was observed, then a second (counter) neck appeared, while further tension led to the appearance of the third stable neck in which fracture occurred. In the case of more complex oscillating shape of σ–ε curve the multiple running necks were observed. The movement of the multiple necks propagating along the sample leads, ultimately, to a uniform picture of the deformation and made it possible to achieve the strain values observed in superplasticity mode.

Some factors affecting the quality of magnetic force microscopy images are considered. The main attention is paid to the deterioration of the quality of scans caused by contamination of the probe. It is shown that contamination can occur both during scanning and during storage of the probe. These two different sources of contamination show up differently in images, and different methods must be used to eliminate them. A likely source of probe contamination is the gel used in probe storage and shipping boxes. The magnetic coating of cantilevers can be a catalyst for a chemical reaction leading to the formation of liquid hydrocarbons. The liquid contaminants act as probe functionalizers. When the probe is moved away from the surface, mechanical bonds can be maintained between them due to the molecular chains adsorbed on the probe. Depending on the degree of pollution, the presence of such a connection can lead either to the appearance of stripes in the image of the magnetic structure, or to the complete disappearance of the magnetic contrast. A modification of the standard procedure for magnetic measurements, i.e., the introduction of an additional bounce into the two-pass technique (lift mode), makes it possible to completely eliminate the parasitic influence of this effect.

The results of studying the neutron irradiation effect on the spectral characteristics of In_xGa_{1 – x}N LEDs are presented. The mechanism responsible for the shift of the emission spectra maximum of LEDs under the neutron influence has been determined. The coherence is shown between the radiation sensitivity of the spectral characteristics of the sample active layers and the composition of In_xGa_{1 – x}N solid solution. An analytical calculation has been carried out to estimate the possible maximum shift of the luminescence spectrum of In_xGa_{1 – x}N LEDs after neutron exposure.