Surface Engineering and Applied Electrochemistry最新文献

The paper presents a theoretical study of the behavior of an ionic boundary layer that occurs in the process of a steady proton exchange in a benzoic acid melt contacting with the surface of a lithium niobate crystal. The penetration of protons into a crystal promotes the injection of oppositely charged ions (lithium and benzoate) from the surface of lithium niobate in the surrounding acid. The transfer of the reaction products and their interaction in benzoic acid is studied numerically. The proposed mathematical model includes the effect of recombination in the volume so that the ions with different charge signs approach each other and form a neutral lithium benzoate. The results of the numerical simulations demonstrate that there are exponential-like concentration profiles of two types of ions, and a non-uniform electric field and pressure distributions develop in the boundary layer under steady-state conditions. In this process, the total charge of the system remains zero. It is shown how the concentration, recombination, and activity of lithium and benzoate ions and the diffusion coefficients affect the profile shapes and the process intensity.

The paper presents the results from studies of the electrical and magnetic properties of an inhomogeneous percolated medium based on the theory of percolation. The application of this theory has a wide and varied range. Examples include hopping conductivity in semiconductors, properties of porous materials, etc. It was found that, with approaching the percolation threshold p_c = 0.35, the resistivity decreases, and the electrical conductivity increases accordingly. An increasing number of individual ferromagnetic nanogranules in (p)–Fe₂O₃–(1–p) (MBT) composites merge with the formation of individual Fe₂O₃ clusters in the bentonite matrix, which combine to form a continuous network of clusters. This is due to the fact that the resistivity ρ of the composite is mainly determined by the magnetic component of the latter.

The anodic dissolution of type Kh18N10 (Cr18Ni10) chromium–nickel steel was performed in a nitrate solution (conductivity of 0.15 S/cm) under pulsed current conditions using pulse durations of 20–100 µs, current densities of 0.01–100 A/cm², and relative pulse durations of 10 to 1 (duty cycle from 10 to 100% (direct current), respectively). Different hydrodynamic conditions were implemented, and the surface temperature was measured. The results obtained are in line with the hypothesis that the process is mediated by the formation of a semiconducting anodic oxide film with point defects that can exhibit different types of conduction. The film is described within point defect model II, and the rate of its electrochemical formation is balanced under steady-state conditions by the rate of its chemical dissolution, which is why the mass decrease per unit charge reaches a limiting value of 0.16–0.18 mg/C (under the pulsed conditions), which corresponds to a current efficiency close to 100% (assuming the highest oxidation state for alloying components of the steel in solution). In going from pulsed current to direct current conditions, the thermokinetic instability of the film is observed, i.e., it forms and then undergoes breakdown due to thermal explosion. Under such circumstances, the current yield of anodic dissolution may not only reach 100%, assuming the lowest degree of oxidation of the alloying components (thermal activation), but exceeds this value as a result of chemical interaction between the film-free surface and the electrolyte.

Hydrogen sulfide is a corrosive species responsible for the deterioration of metals and alloys in marine environment. In this study, the electrochemical performance of the 90/10 Cu–Ni alloy in stagnant and aerated 3.5% sodium chloride (equivalent chloride concentration in seawater) containing 0.01 M Na₂S was investigated using potentiodynamic polarization technique at 23, 50, and 80°C. The surface examination and morphological studies were also employed. Polarization measurements in sulfide-infested environments revealed that 90/10 Cu–Ni alloys are adversely sensitive to the sulfide presence and exhibit very high corrosion rates at higher electrolyte temperatures in accordance with an exponential fashion. In addition, the confirmation of a corrosion attack evidencing a pitting type corrosion appearing after the metallographic characterization was applied.

Many industries face corrosion problems caused by the medium containing chloride ion due to its aggressive nature. The implementation of corrosion inhibitors has been recognized to be the easiest and most inexpensive approach for corrosion mitigation. Plant extracts as inexpensive, nontoxic, and biodegradable materials are found abundantly in nature. The heteroatoms, and polyfunctional groups of the active constituents present in plant extracts, make them potential candidates as corrosion inhibitors for metals. The present review includes a compilation of to-date investigations of aqueous extracts of various parts of plants for the corrosion inhibition of mild steel in the NaCl medium only. The inhibition efficiency of various plant extracts was reported based on electrochemical techniques. The type of action, the mode of adsorption, and the mechanism of inhibition were also explored. The surface characterization and theoretical accepts are explained briefly as a support to the experimental results.