Volume 59, Nº 4 (2023)

A generalization of the procedure for calculating the local mechanical moduli of multicomponent porous materials in the process of adsorption deformation by a mixture of adsorbed molecules is discussed. The porous system is modeled by a two-level structural model consisting of interconnected systems of globules/grains and a system of pores inside which adsorption occurs. The adsorbate simultaneously affects the outer and inner surface of the adsorbent, changing the volume of the sample with a fixed amount of adsorbent. Based on two-level structural models of deformable porous bodies within the framework of the lattice gas model, equations are formulated that provide a self-consistent description of the change in their volume and partial adsorption isotherms as a function of the external pressure of the adsorbate at a fixed temperature. For simplicity of presentation of the calculation scheme, commensurability of the sizes of the atoms of the solid body and the components of the mobile phase of the adsorbate is assumed. The molecular level reflects the intrinsic volume of molecules and their lateral interaction in the quasi-dimeric approximation. The supramolecular level of the model is represented as a grain of a porous material with a given distribution function of interconnected pores of various types and sizes. Using the compression modulus as an example, a method for calculating average local mechanical moduli characterizing the mechanical properties of solids is considered.

The results of studying the sorption of copper(II) ions by composite sorbents based on chitosan and mineral reinforcing fillers from aqueous solutions of electrolytes and solutions containing dodecyldimethylamine-N-oxide are presented. It is shown that the composite sorbents “chitosan–glauconite” and “chitosan–zeolite” are characterized by a larger increase in the sorption capacity for Cu(II) ions in solutions containing surfactants than the composites “chitosan–silicon dioxide” and “chitosan–montmorillonite.” The adsorption characteristics of the composite sorbents were compared with those of the initial hydrogel chitosan sorbent. IR spectra, diffraction patterns, and micrographs of the surface of the samples were obtained.

For the first time, using solution technology in a reactor under pressure, composites of titanium oxide and LTA zeolite containing 50, 70, and 80% TiO2 were obtained. The materials were characterized by XRD, IR spectroscopy, SEM, energy-dispersive microanalysis, and low-temperature nitrogen adsorption–desorption. The adsorption and photocatalytic properties of the composites were studied using the model dye Rhodamine B as an example. The surface morphology and the textural, adsorption, and photocatalytic properties of the resulting composites, as well as the phase composition of TiO2, largely depend on the degree of coverage of the surface of the zeolite. For 80% TiO2/LTA composites, a degree of coverage close to 100% was observed, and it is for this composition, with a size of TiO2 crystallites of about 11 nm and an anatase/rutile phase ratio of about 0.54, that the highest photocatalytic activity was found.

The formation process of spectrally selective coating–absorbers of optical radiation with a high absorption coefficient obtained by thermal oxidation of X18H10T high-chromium steel for 1 h in an air atmosphere at temperatures of 100–900°C has been studied. The composition of the films and their thickness were controlled using diffuse reflection Fourier transform IR spectroscopy and specular reflection spectral reflectometry. It is shown that thick oxide layers (up to 1400 A) with high absorption in a wide range of wavelengths of solar radiation are obtained by thermal oxidation of steel plates at 800–900°C. Unfortunately, thick porous coatings obtained by air oxidation of steel at high temperatures have low mechanical strength, and porous coatings can crack and crumble. Thinner oxide layers (400–800 A) with a low content of chromium oxides, formed during the oxidation of steel at 500–600°С, make it possible to obtain spectrally selective absorption sufficient for the operation of the corresponding optical radiation converters in the visible range. Such layers are much stronger, more compact, have a high optical quality and a multilayer and/or gradient structure, make it possible to form one- and two-layer interference coatings of the required thickness and composition, have high absorption and a pronounced photoelectric response in the spectral regions of visible solar radiation.

The results of a study of the features of selective laser melting (SLM) of the aluminum powder modified with V2O5 gel in an amount of 0.8 wt % are presented. It has been shown that, in the process of SLM on an EOS M 280 printer, it was impossible to obtain a material with the required porosity. It has been established that the reason for the excessive porosity of the samples consists in a high rate of heating and cooling of powders during the melting process and the formation of low-melting phase components (AlVO4, V2O5). The temperature conditions of the process (heating and cooling rates) do not allow the synthesis of intermetallides of the Al–V system during SLM to change the functional properties of aluminum. It has been shown that the positive effect of V2O5 on the melting of aluminum particles is possible by reducing its concentration on the surface of the Al powder to values that are only sufficient to ensure the destruction of the existing oxide layer.

The Mo–Si–B and Mo–Y–Si–B coatings were obtained by magnetron sputtering in the direct-current mode using a 90% MoSi2 + 10% MoB target equipped with yttrium segments. The composition and structure of the coatings were studied by scanning electron microscopy, X-ray phase analysis, and optical emission spectroscopy of a glow discharge. The diffusion-barrier properties and heat resistance were evaluated by annealing at temperatures from 700 to 1000°C. The thermal stability was determined by heating the coating lamellae in a column of a transmission electron microscope in the in situ mode. According to the chemical analysis, the main elements were evenly distributed over the thickness of the coatings. The coating growth rate did not change upon the introduction of yttrium and was in the range of 325–350 nm/min. The Mo–Si–B coating was characterized by a columnar structure with grains of the hexagonal phase h-MoSi2 about 50 nm in size, as well as an insignificant volume fraction of the boron-containing amorphous phase (a‑MoB). An increase in the concentration of Y up to 4 at % led to a decrease in the size of h-MoSi2 crystallites of up to 10 nm. A coating with a maximum concentration of yttrium (7 at %) contained predominantly an amorphous phase a-MoB with phase crystallites dispersed in it h-MoSi2 and t-MoB. The introduction of the optimal amount of yttrium (4 at %) led to a decrease in the thickness of the oxide film by a factor of 6 after annealing at a temperature of 800°C and by three times at 900–1000°C. The coating with the maximum concentration of yttrium (7 at %) had the best diffusion-barrier properties of all the studied samples at 700–1000°С, and also surpassed the Mo–Si–B sample in terms of thermal stability. Positive effects from the introduction of yttrium into the composition of the coatings were connected with (a) structure modification, including suppression of columnar grain growth; (b) transition to a structure with a higher volume fraction of the amorphous phase; (c) isolation of grain boundaries and lengthening of the diffusion path of metal atoms from the substrate; and d) formation of protective surface layers on based on yttrium oxide when heated in air.

Research has been carried out on the development of compositions of protective coatings based on TiB2 and various carbon fillers, as well as the method of their application to cathode blocks of aluminum electrolyzers. The physical and chemical properties (surface morphology of particles, granulometric and phase composition) of initial powders of titanium diboride and the physicomechanical properties and microstructure of laboratory samples of protective coatings are determined. It is shown that compositions based on TiB2 and MKhNU carbon filler (low-shrinkage cold-filled mass) are most promising. High-temperature tests of laboratory samples of coatings of optimal composition with the addition of 50% MKhNU were carried out, which showed that the coating is wetted by aluminum melt and reduces the wear of cathode blocks. A 20-mm-thick coating was locally applied to the experimental electrolyzer bottom in the form of 900-mm-wide strips along the electrolyzer sides, taking into account the wear profile, and is currently undergoing industrial tests. Results of monitoring the titanium content in the metal for 196 days after the electrolyzer startup show the effectiveness of using the developed coating to protect cathode blocks from wear and increase the service life.

A comparative analysis of the barrier properties and corrosion resistance of bioinert coatings of tantalum, zirconium nitride, stainless steel of the 12X18H10T grade, as well as diamond-like coating (DLC) deposited on the surface of the medical alloy Ti–50.8 at % Ni (TiNi) has been performed. All the coatings are characterized by high barrier properties with respect to the yield of nickel in the biological medium for a long time, whereas, in the case of uncoated TiNi, the concentration of nickel in the test solution increases rapidly and exceeds the permissible amount of migration after 60 days of exposure. Electroplating TiNi–bioinert-coating pairs demonstrate a corrosive behavior determined by the nature of the coating material. The most resistant to galvanic corrosion is the TiNi –Ta pair, for which no signs of corrosion processes were detected on any of the elements of the pair after exposure in a model solution for 24 h. The pairs TiNi–12X18H10T and TiNi–DLC have shown the worst corrosion resistance among the studied pairs: extensive corrosion areas were observed on one of the elements of the pairs.

An acetone-neutral adsorption-based sensor of exhaled air humidity was developed for potential use in the diagnosis of diabetes mellitus. The sensor was made use a molecular sieve of KA zeolite, a granule of which was is glued to the plate of the quartz resonator of longitudinal oscillations. The sensor sensitivity threshold for water vapor was 0.05% of relative humidity. Due to the molecular-sieve effect, the acetone molecules penetrate to the zeolite pores only at concentrations above ~5%. Therefore, the sensor is sensitive to water-vapor adsorption, but not to acetone vapor and other volatile organic compounds that are present in exhaled air. The content of acetone and other biomarkers of diseases can be detected by a special sensor intended for the diagnosis of diabetes mellitus, lung cancer, alimentary-system organ dysfunction, and other diseases.