No 4 (2023)

Carbon fibers are used in the production of automobiles, airplanes, sporting goods, energy, and biomedicine due to their unique properties such as high specific strength, high specific tensile strength, low coefficient of thermal expansion, and low density. The research and development of both the technology of carbon fibers production and their modification for a wide range of applications have been and remain relevant. The summary of the accumulated experience in the modification of carbon fibers shows that ion-beam treatment allows to obtain a variety of geometry of the developed surface topography, in particular, whisker-shaped and corrugated oriented across or along the fiber. Such processing compares favorably with ordinary fiber whiskering both by a variety of geometry of the composite interface, and by the absence of the problem of whisker-fiber adhesion. Ion-beam treatment also makes it possible to modify the surface layer structure from amorphized to ordered with different degrees of graphitization. Irradiation with chemically active ions leads to functionalization of carbon fiber due to formation, for example, of nitrides and carbon oxides. The choice of nitrogen ions for the technology of carbon-carbon and carbon-ceramic composites seems to be more preferable due to less stringent requirements for the temperature of the irradiated fiber. For ion-beam corrugation of polyacrylonitrile-based carbon fiber surface, only its heating above the temperature of dynamic annealing of radiation damage is required. The use of helium ions in technological plasma acceleration systems leads to a significant efficiency increase in ion-beam processing.

The possibility of using specular neutron reflectometry to study aqueous trisiloxane solutions during the transition to the superwetting state was shown. The adsorption of trisiloxane surfactants from solution onto a moderately hydrophobic surface (oxidized titanium film) with increasing temperature up to the cloud point of the solution was considered. To clarify the role of the hydrophobic part of trisiloxane surfactant molecules in the superwetting effect, a comparison was made with solutions of a nonionic hydrocarbon surfactant with similar polyoxyethylene chains.

The magnetic ordering of the multilayer structure of Dy–Co was studied using complementary methods of polarized neutron reflectometry and Kerr magnetometry. It was found that during the deposition of a layered structure, the Dy and Co layers are partially mixed with the formation of the DyCo₂ intermetallic compound. The profiles of the magnetization of individual layers at the atomic level were determined. It was managed to describe a noncollinear magnetic structure of the layers near the compensation point using the neutron reflectometry data. The triple hysteresis loops observed in the same temperature range most likely indicated the non-identity of the outer and inner superlattice layers. The inhomogeneity profile of the DyCo₂ layer magnetization distribution can be explained by the strong exchange interaction at the interfaces. In a small applied magnetic field, the interlayer exchange interaction dominates over by the Zeeman energy. The antuparallel ordering of the magnetic moments of the Co and DyCo₂ layers was distorted by the magnetic field; as a result, the angle between the magnetization vectors was maximum at the Co/DyCo₂ interfaces only.

The adaptation of neutron scattering methods for studying the microstructure of electrode materials of lithium-ion batteries was continued in order to improve their characteristics with respect to specific energy. Using small-angle scattering of thermal neutrons, the effect of conductive carbon additives (graphene and graphene oxide) on the porous structure of electrodes made from LiFePO₄, Li₄Ti₅O₁₂ and LiNiMnCoO₂ was studied. To separate the scattering by closed and open pores, the electrodes were wetted with a typical liquid electrolyte with a deuterated liquid carrier (dimethyl carbonate), which led to the matching of scattering by open pores. It was established that the electrically conductive carbon additives changed the electrode porosity to varying degrees and affected the wettability of materials both due to different degrees of penetration into the pores of the source material and due to the effect on the initial matrix. A universal effect on the scattering of polymer binder (polyvinylidene fluoride) was also found.

A new method for determining the coordinates in position-sensitive detectors with an organic fiber and silicon photomultipliers is described. This method differs from previously used spectrum-shifting fibers or an array of light-sensitive elements. It is based on the absorption of photons in the volume of the fiber and the reduction in the number of photons. Depending on the path length, the number of photons incident on the surface of the silicon photomultiplier varies. The optical parameters of a one-dimensional position-sensitive detector are simulated and the effect of the fiber coating on the amount of light is shown. Simulation of a two-dimensional position-sensitive detector of two types has been also carried out, optical parameters and intensity ratios from different ends of the fiber have been determined. A technique for obtaining maps of intensity ratios and features of their use for determining the coordinates are described. The main features of the manufacture of this type detectors and their influence on the resolution of the final detector are outlined.

Neodymium molybdate with a cubic fluorite-like structure was obtained by solid state reactions from metal oxides. The formation of the final product occurs through the formation of a monoclinic structure of Ln₂MoO₆ type (space group C2/c) at 700°C, which probably contains vacancies in neodymium and oxygen lattices. Neodymium molybdate obtained at 900°C crystallizes in the space group Pn\(\bar {3}\)n with the cell parameter a ≈ 11.039 Å. The crystal structure of neodymium molybdate obtained at 700 and 900°C was studied by neutron diffraction and atomistic modeling using the GULP program in the pressure range 0–5.9 GPa, which demonstrated the stability of the cubic structure at elevated pressure.

The process of metal atoms sputtering during a corona discharge is considered. When an electron moves in a medium at some velocity, charge screening occurs with a delay in space and time, which leads to the emergence of a wake potential. The excited oscillations of the wake charge lead to the appearance of additional forces. The energy loss of a moving particle per unit path is determined by the work produced of the deceleration force that acts on the particle from the side of the wake potential it creates in the medium. The paper considers the effect of the wake potential on the ions (atoms) sputtering of the lattice matrix. A well-known expression is used for the wake potential excited by a charged particle moving with energy, greater than the Fermi energy. An expression for the sputtering cross-section of metal atoms under the action of the wake potential excited by the electron beam is obtained. It is shown that the result of sputtering does not depend on the charge sign of the incident particle (electron or ion).

Two ancient Roman silver coins dating back to the 3rd–4th century AD were studied. A set of modern micro- and non-invasive analytical techniques was used: a focused ion beam, scanning electron microscopy, energy dispersive X-ray microanalysis, micro-X-ray fluorescence analysis, neutron radiation analysis, and other methods. The research showed that Ag–Cu and Ag–Cu–Pb–Sn alloys were used, common in the prosperous years of the Roman Empire, when the Romans produced alloys with a relatively high silver content for both outer layers and the inner core of the coins. Surface silvering processes were used during different periods of crisis under the reign of Antoninii. It was established that even during the crisis, the Romans produced high quality “Antoninianus”, attempting to improve the silvering procedure using silver amalgam (Hg–Ag) – mercury was detected in the near-surface silver layer of the coins. A porous morphology of the coin surface was also revealed, which might be the result of an uncontrolled heating process and the removal of mercury through boiling.