Protection of Metals and Physical Chemistry of Surfaces最新文献

Electrodeposition of composition modulated multilayer (CMM) coatings of Ni–Co alloy was accomplished on mild steel using single bath technique (SBT). Multilayer coatings, having layers of alternatively different compositions have been produced on the mild steel using the electrolytic bath having both Ni and Co ions by periodic pulsing of the current density between two set values, known as cyclic cathode current densities (CCCD’s). The deposition conditions, in terms of the composition and thickness of alternate layers were identified for best performance of those coatings against the corrosion. Electrochemical corrosion study of alloy coatings has been made using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. It was found that CMM(Ni–Co)_1.0/3.0/60 coatings shows approximately three times better corrosion resistance than its monolayer counterpart, deposited from same bath for same duration. The experimental study demonstrated that corrosion protection efficacy of CMM Ni–Co alloy increased with number of layers up to 60 layers, and then started decreasing. The observed increase of corrosion rate at high degree of layering (after 60 layers) was attributed to the diffusion of layers, affected due to rapid change of current densities during deposition. Improved corrosion protection efficacy of multilayer coating is attributed to the alternate layers of alloys having different composition, confirmed by energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The deposited coatings were analyzed for both surface and cross-sectional features using scanning electron microscopy (SEM), and results are discussed.

This study aimed to investigate the preparation of composite films made from cassava starch (CS) of the Khaek Dam cultivar and polyvinyl alcohol (PVA), crosslinked with citric acid (CA) at various concentrations 0, 0.1, 0.3, 0.5, and 0.7% (based on the dry weight of CS). The results showed that film thickness increased with higher CA concentrations. The water activity (a_w) of the films ranged from 0.40 to 0.43. At 0.3% CA, the water solubility, water absorption, and water vapor permeability of the composite film decreased, while puncture strength and tear strength increased. However, at higher CA concentrations (0.5–0.7%), water solubility, water absorption, and vapor permeability increased, while puncture and tear strength decreased. Biodegradability tests showed that the composite films degraded by 36.84 to 53.39% for 8 weeks. When used as banana packaging, the composite film containing 0.3% CA demonstrated the highest efficiency in extending shelf life, maintaining freshness for nearly 7 days longer compared to bananas not sealed with the composite film. These findings suggest that the composite film made from CS and PVA, crosslinked with 0.3% CA, offers the most favorable overall properties-both in terms of physical and mechanical properties as well as fruit preservation potential. This highlights its promise for future development as a biodegradable polymer film for food packaging applications.

Composite electrochemical coatings (CECs) based on nickel and Ti₃C₂T_x MXene were obtained from a sulfate-chloride electrolyte in galvanostatic mode. Microstructure of these CECs) was studied using X-ray phase analysis and scanning electron microscopy. It was found that the microhardness of nickel–Ti₃C₂T_x CECs increases by approximately 1.80 times compared to pure nickel. The corrosion-electrochemical behavior of nickel–Ti₃C₂T_x composite coatings in 0.5 M H₂SO₄ was studied. Based on tests in 3.5% NaCl, it was found that the inclusion of Ti₃C₂T_x MXene particles in the electrolytic nickel matrix leads to a decrease in the corrosion rate by 1.60–1.75 times.

This paper proposes a method for increasing the corrosion resistance of a titanium alloy based on its polarization with an alternating current of infra-low-frequency in an electrolyte of the composition 1 g/L PdCl₂ + 1.0 M NaCl. Scanning electron microscopy and Auger spectroscopy showed that particles of a new phase—elemental palladium with a particle size in the range of 0.050–0.500 μm—were detected on the modified sample surface in all areas of analysis. In addition, the accelerated corrosion tests in a concentrated HCl environment (5.0 M) were carried out to evaluate the anticorrosion properties of the surface-alloyed titanium-alloy sample. A significant shift in the potential values to more positive values (up to 300 mV) of the studied titanium-alloy sample with a local coating indirectly indicates an increase in its corrosion resistance.

Deformation behavior of hydrogenated dentin from intact human teeth was studied in shear testing at room temperature, and the dependence of its mechanical properties on specimen thickness and the degree of dentinal canal filling with water was determined. It was shown that, regardless of specimen thickness and the degree of dentinal canal filling with water, the dentin deformation behavior is similar to that of viscoelastic filled polymers, whereas the dentin’s failure mode in shear was characterized as brittle fracture. It was found that the deformation behavior of thick hydrogenated dentin specimens is independent on the degree of dentinal canal filling with water, which significantly affected only the behavior of thin specimens.

The adsorption processes of nitrogen and neon onto carbon adsorbents were investigated at pressures between 1 and 1.013 × 10⁵ Pa and temperatures of 77 and 27 K. The isotherms of adsorption were measured, the specific micropore volumes were determined, and the characteristic energies of adsorption were evaluated for these adsorption systems. The theory of volume filling of micropores was utilized to calculate the isotherms of neon adsorption onto different microporous carbon adsorbents using the affinity coefficients.

The influence of chemical modification on the sorption properties of apple pectin in relation to Mn²⁺ ions was studied. Pectin was modified with aromatic amino acids (L-histidine, L-tryptophan, L-phenylalanine) in an aqueous medium at pH 7. An increase in the extraction efficiency (by 12.6–21.4%) of Mn²⁺ ions of modified pectin sorbents was detected compared to the original polysaccharide, which is due to changes in their physicochemical characteristics and the appearance of new sorption centers in the structure. The values of thermodynamic parameters indicate the occurrence of a chemical adsorption process (∆H° = –42.6 to –24.3 kJ/mol). It is shown that sorption on modified pectins is best described by the Langmuir isotherm.

A method is described for producing a microporous carbon sorbent based on a heavy oil refining residue—petroleum asphalt—which, after carbonization at 500°C, was mixed with potassium hydroxide in a ratio of from 4 : 1 to 1 : 1 in an AGO-2 planetary centrifugal mill with a centripetal acceleration of the grinding media of 1000 m/s², followed by high-temperature activation at 800°С for 60 min. For the obtained samples, adsorption isotherms were measured of pure gases of CO₂ gases and CH₄ at 273 and 298 K. Thus, for samples obtained with a KOH/asphalt ratio of 1 and 2, at 273 K and 1 bar, the adsorption capacity for CO₂ and CH₄ amounted to 5.6–5.9 and 2.2 mmol/g, respectively. The best CO₂ adsorption capacity at 273 K and 1 bar in the studied series of samples—6.3 mmol/g—was obtained for the KOH : asphalt = 3 : 1 sample. It was found that mechanical activation of asphalt and KOH promotes the formation of carbon materials with a more developed porous structure, namely, an increase in textural characteristics by 30% compared to samples prepared without MA. Thus, the presented approach of using mechanical and chemical activations contributes to the production of porous carbon that meets the requirements of adsorption separation of a mixture of methane and carbon dioxide gases.

Within the framework of the thermodynamic theory of equilibrium two-component adsorption from a liquid on a flat solid surface, taking into account its deformation and the presence of an electric charge on it at small deformations of the solid phase, an expression for the increment of the surface tension of the interfacial layer as a function of four parameters of the state of the equilibrium system—two adsorption densities of both components, the electric potential, and the deformation of the solid surface—is derived analytically for the Frumkin surface layer model.