Protection of Metals and Physical Chemistry of Surfaces最新文献

This brief review considers the main approaches to the processing of used lithium-ion batteries. A description of the initial raw materials depending on the elemental composition of the cathode material is presented. The main currently developed methods of processing of batteries—namely, pyrometallurgical, hydrometallurgical, and direct processing—are briefly described. A hydrometallurgical method is recognized as the most optimum one. A description of the main process stages, namely, stages of preliminary treatment of batteries, alkaline treatment of the fine fraction that is a mixture of the anode and cathode materials, acidic leaching of the cathode material, and subsequent processing of the leaching product to isolate individual valuable components from it is presented for the said process.

Novel results about the practical adhesion of the layer/substrate system on borided and borocarburized AISI 8620 steels exposed to a quenching-tempering post-treatment were obtained. The hardness (H) and Young modulus (E) were assessed by instrumented Vickers microindentation. Consequently, the residual stresses (σ_r) and elastic strain to failure (H/E) were estimated. The microstructural characterization of the entire experimental set was carried out by scanning electron microscopy (SEM). Finally, the practical adhesion of the experimental set was evaluated with a scratch test, using a progressive load from 1 to 150 N at 10 mm min^–1, with a scratch length of 7 mm. The results indicated that the quenching-tempering treatment increased the practical adhesion of the layer/substrate system, due to the dissolution of the outer FeB phase on the boride layer. Furthermore, the borocarburized material showed an increase around 2 times of the critical load during the practical adhesion test, attributed to a greater depth of the compressive residual stresses along the boride layer and the carburized zone. The borocarburizing + quenching-tempering treatment provided a mechanical support to the AISI 8620 steel, reducing the brittleness of the layer, in comparison with the borided and borided plus quenching-tempering material.

This study investigated the effect of the modifying additive hemicurcuminoid HCur on the sensory ability of monolayers and ultrathin films based on polydiacetylene 10,12-pentacosadiynoic acid (PCDA; the polymerized form is denoted as polyPCDA). Using UV-Vis and fluorescence spectroscopy, it was established that in both the monocomponent and modified systems, when exposed to a lead perchlorate solution, either in the monolayer at the air–water interface and in the films formed from it, a chromatic transition from the blue nonfluorescent form of polydiacetylene (PDA) to the red fluorescent form occurs. The presence of the hemicurcuminoid HCur in the system leads to an increase in the colorimetric response of the transition and a significant growth of the fluorescent response. It has been demonstrated that the optical sensory responses of mixed polyPCDA–HCur monolayers and films are significantly higher than those of similar monocomponent Langmuir polyPCDA systems. It has been shown that the hemicurcuminoid HCur actively participates in the coordination binding of lead ions, apparently through the deprotonated enol form, as evidenced by the quenching of the dye fluorescence with a simultaneous increase in the intensity of its absorption bands. Moreover, the presence of HCur significantly enhances the optical response of polyPCDA to lead cations, indicating the manifestation of a synergistic effect of such modification. The described results may serve as a reason for further study of this system in order to develop a highly sensitive, selective two-signal sensor for lead ions in an aqueous environment.

General comparative studies were conducted on changes in the surface, physical and mechanical properties of bioresorbable sutures in vitro and in vivo, and tissue reactions to the use of suture materials with different biodegradation times: copolymer of lactide with glycolide (PGL), polydoxanone (PDO), and copolymer of glycolide and ε-caprolactone (PGK). The cause of the possible inflammatory tissue reaction has been determined. The biodegradation process for all sutures begins from the surface and is accompanied by the “leaching” of low-molecular substances, the mechanism of bioresorption is phagocytic, the sutures are considered by biological tissues as foreign bodies. However, depending on the chemical composition of the suture material, the local tissue reaction differs somewhat. Thus, in the case of PGL, an increase in the number of multinucleated Pirogov–Langhans giant cells phagocytizing particles of suture material is observed; when using PDO sutures, an increase in the number of lymphocytes with a ring-shaped nucleus predominates, as in the case of PGC sutures. The tissue reaction also depends on whether the suture material is monofilament or braided. In monofilaments, the bed, the connective tissue “case,” is clearly visible; in braided sutures, the fibers grow into connective tissue, forming giant multinucleated cells, which can lead to the formation of granulomas and “connective nodules.” In all variants of bioresorbable sutures, after complete loss of strength, they turn into oxyphilic heterogeneous substances on histological sections, which is confirmed by the differential scanning calorimetry method; amorphization of the supramolecular structure of the polymers is noted. At the initial stages of bioresorption of suture materials, the mechanism of change in the supramolecular structure of polymers in vivo and in vitro varies: usually in vitro the changes go through a recrystallization stage, and in vivo, through gradual amorphization. Therefore, let us explain the fact that, under biological tissue conditions, the strength of the suture at different stages of wound healing can be 5–10% lower than in vitro, which is, however, being within the confidence intervals, which allows the method to be replaced if necessary in vivo or in vitro until a residual strength of 50% is reached.

The atomic–electronic and defect structure of various carbon materials—crystalline diamond and CVD diamond films, single-crystal and polycrystalline graphite, technical carbons with different specific surface areas and oxidation states, activated carbons, and carbon nanofibers—has been studied using the positron annihilation method. It has been found that the shape of the angular distribution of annihilation radiation (ACAR) for carbon nanofibers differs from that of both graphite and diamond materials. A noticeable broadening of the ACAR compared to that of polycrystalline graphite has been recorded. It has been shown that the carbon–carbon bonds are stressed and the shortest distance between adjacent carbon atoms is reduced compared to graphite. The presence of adjacent planes in the helical structure of the nanofiber also increases the degree of localization of annihilating valence electrons. All this leads to the observed broadening of the ACAR in nanofibers.

The design of advanced self-lubricating ceramic nanocomposites is crucial for applications that demand high wear resistance and reduced friction under severe operating conditions. In this study, Al₂O₃, yttria-stabilized zirconia (YSZ), carbon nanotube (CNT) nanocomposites were fabricated via spark plasma sintering (SPS) to investigate their structural, microstructural, and tribological performance. The incorporation of CNTs and YSZ into the Al₂O₃ matrix resulted in dense, well-bonded composites with a uniform distribution of reinforcements. Wear tests performed under different loads revealed that the hybrid nanocomposites exhibit a significant reduction in wear rate and coefficient of friction compared with monolithic Al₂O₃. The enhanced wear resistance was attributed to the synergistic effects of YSZ-induced toughening, the lubricating role of CNTs, and the formation of protective tribofilms during sliding. Among the compositions, the optimized sample demonstrated the lowest wear loss at both 10 and 15 N loads, confirming its suitability for demanding tribological environments. Overall, this work highlights the effectiveness of combining Al₂O₃, YSZ, and CNTs in achieving multifunctional nanocomposites with promising potential for high-performance wear-critical applications.

It is shown that high-energy impact on the phase boundary by the method of pulsed microplasma oxidation with a trapezoidal pulse shape leads to localization of high-density energy in the near-electrode layer, bifurcation of the electrolyte flow, restructuring of the phase boundary, and fragmentation of the boundary hydrodynamic layer. The processes of phase-boundary restructuring and boundary-layer fragmentation, which affect the structure of porous oxide coatings, were determined and modeled. It has been shown that fragmentation leads to the appearance of ring structures, which are then reconstructed into more complex and larger structures, inside which small-diameter pores remain, with a porous oxide coating being formed. Differences have been identified elemental composition in the center and at the boundary of the boundary-layer fragment, caused by different rates of electrochemical reactions in different parts of the fragment.

The adsorption behaviors of microporous carbon adsorbent ASK-1 with respect to CO₂ capture from the CO₂/N₂ mixtures were investigated at temperatures of 233, 273, and 313 K at pressures up to 1000 kPa. The activated carbon with the micropore pore volume of 0.53 cm³/g and the specific BET surface of 1440 m²/g was prepared from coal-tar raw materials of Kamchatka krai (Russia) by chemical activation using KOH at a temperature of 1173 K. The isotherms of one-component adsorption of gases were calculated using the Dubinin–Radushkevich equation of the theory of volume filling of micropores. The adsorption equilibrium of the СО₂/N₂ mixtures with the CO₂ content ranging from 0.05 to 20 mol % were calculated using the ideal adsorption solution applied to the isotherms of individual gases in order to evaluate the efficiency of the adsorbent for capturing CO₂, as well as to identify the optimal conditions for separating the СО₂/N₂ mixture. The availability of ASK-1 to purify air from technogenic CO₂ was determined by analyzing the adsorption behaviors of the components and estimating the potential CO₂ selectivity of the adsorbent as a function of the mixture composition, pressure, and temperature.

This study investigated the microstructural and corrosion resistance modifications in Mg–0.8% Si alloy with Sn addition. Sn effectively refined Mg₂Si morphology and distribution. Mg–8% Sn–0.8% Si consisted of α-Mg, Mg₂Si, and Mg₂Sn phases, with Mg₂Sn enriched at grain boundaries. Sn significantly enhanced corrosion resistance by 14–17 times, with limited improvement beyond 8% Sn. Mg₂Sn formation, SnO₂ layer, and fine Mg₂Si barrier contributed to improved corrosion resistance.

Thermogravimetry, differential scanning calorimetry, and scanning electron microscopy were used to study the change in the structure of particles of metal-oxide composites obtained by compacting iron powder and subsequent annealing with an increase in temperature from 20 to 800°C in air and in an argon atmosphere. It is shown that, after high-temperature annealing, vacancy pores and cavities are formed in the volume of metal-oxide particles of the composite, which are associated with the external diffusion of metal ions through the oxide layer and counterdiffusion and injection of vacancies into the metal with their subsequent condensation into pores in the internal volume of metal-oxide particles (the Kirkendall effect). The reason for the acceleration of diffusion of metal cations and vacancies is associated with the presence of a difference in internal stresses in the growing oxide layer on the surface of the metal particles of the composite. It has been shown that differences in the diffusion coefficients of cations and anions through the oxide layer (the Kirkendall effect) can be used to synthesize hollow iron-oxide particles and composite materials based on them, which can be used for encapsulation and as adsorbents, as well as to create new types of hybrid materials for catalytic or biological applications.