Anodizing of Hydrogenated Titanium and Zirconium Films

Magnetron-sputtered thin films of titanium and zirconium, with a thickness of 150 nm, were hydrogenated at atmospheric pressure and a temperature of 703 K, then anodized in boric, oxalic, and tartaric acid aqueous solutions, in potentiostatic, galvanostatic, potentiodynamic, and combined modes. A study of the thickness distribution of the elements in fully anodized hydrogenated zirconium samples, using Auger electron spectroscopy, indicates the formation of zirconia. The voltage- and current-time responses of hydrogenated titanium anodizing were investigated. In this work, fundamental possibility and some process features of anodizing hydrogenated metals were demonstrated. In the case of potentiodynamic anodizing at 0.6 M tartaric acid, the increase in titanium hydrogenation time, from 30 to 90 min, leads to a decrease in the charge of the oxidizing hydrogenated metal at an anodic voltage sweep rate of 0.2 V·s−1. An anodic voltage sweep rate in the range of 0.05–0.5 V·s−1, with a hydrogenation time of 60 min, increases the anodizing efficiency (charge reduction for the complete oxidation of the hydrogenated metal). The detected radical differences in the time responses and decreased efficiency of the anodic process during the anodizing of the hydrogenated thin films, compared to pure metals, are explained by the presence of hydrogen in the composition of the samples and the increased contribution of side processes, due to the possible features of the formed oxide morphologies.

Theoretical Evaluation for the Assisted Electropolymerization of a Monomer, Obtained by an Indirect Electrochemical Synthesis

In this work, the possibility for indirect electropolymerization of a monomer synthesized by an indirect electrosynthesis has been evaluated. Based on the reaction mechanism, the correspondent mathematical model has been developed and analyzed using linear stability theory and bifurcation analysis. It has been shown that in the case of indirect monomer electrosynthesis and electropolymerization, the polymer deposition is far more stable than for direct participation of the monomer in the electrochemical stage. The surface tends to be more developed. Yet, the electrochemical oscillations are expected to be less probable than in the case of the direct anodic process.

Protective properties of mechanochemically fabricated zeolite/phosphate anticorrosion pigments for paint coatings

The anticorrosion environmentally friendly pigments based on synthetic zeolite and zinc and calcium phosphates were prepared by mechanochemical method. The surface morphology and chemical composition of the obtained pigments were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. It was established that the modification of zeolite by phosphates of divalent metals causes a decrease in the particle size and an increase in the specific surface area of the obtained composite pigments. It was shown that the use of zeolite/phosphate pigments increases the corrosion resistance of the aluminium alloy in 0.1% aqueous NaCl solution. The addition of complex zeolite/phosphate pigments to the sodium chloride solution decelerates the anodic process of electrochemical corrosion, which indicates the formation of a protective film on the metal surface. The composite pigment zeolite/Zn(H2PO4)2 exhibited the highest anticorrosive effect. A gradual release of the inhibitory components from these environmentally friendly pigments provides their long-term action to protect metal products.

Photoelectrochemical Stability under Anodic and Cathodic Conditions of Meso-Tetra-(4-Sulfonatophenyl)-Porphyrinato Cobalt (II) Immobilized in Polypyrrole Thin Films

Cobalt porphyrins have emerged as promising catalysts for electrochemical and photoelectrochemical applications because of their good performance, low cost and the abundance of cobalt in the earth. Herein, a negatively charged porphyrin meso-tetra-(4-sulfonatophenyl)-porphin (TPPS) was immobilized in polypyrrole (PPy) during the electro-polymerization, and then it was metallized with cobalt to obtain meso-tetra-(4-sulfonatophenyl)-porphyrinato cobalt (II) (CoTPPS) as a dopant in PPy. The coatings were evaluated as photoelectrodes towards thiosulfate oxidation and oxygen reduction. For comparison purposes, the photoelectrochemical behavior of ClO4−-doped polypyrrole films was also evaluated. Characterizations by chronoamperometry, UV-Vis spectroscopy and Raman spectroscopy showed that polypyrrole is stable under anodic and cathodic conditions, but CoTPPS and TPPS immobilized in PPy are degraded during the anodic process. Thus, decreases in photocurrent of up to 87% and 97% for CoTPPS-doped PPy and TPPS-doped PPy were observed after a 30-min chronoamperometry test. On the other hand, good stability of CoTPPS and TPPS immobilized in PPy was observed during photoelectrochemical oxygen reduction, which was reflected in almost constant photocurrents obtained by chronoamperometry. These findings are relevant to understanding the role of CoTPPS as a catalyst or pre-catalyst in photoelectrochemical applications such as water splitting. In addition, these results could pave the way for further research to include CoTPPS-doped PPy in the design of novel photocathodes.

Influence of Molybdenum and Tungsten on the Formation of Zirconium Oxide Coatings on a Steel Base

In this paper, we have developed conditions for the deposition of zirconium oxide coatings from solutions containing hexafluorozirconic acid as well as tungsten and molybdenum salts on a steel base. Based on electrochemical studies, it was shown that the addition of tungsten and molybdenum salts to the solution to deposit zirconium oxide coatings led to the inhibition of the anodic process of iron ionization. It was shown that the optimal conditions for the deposition of oxide-zirconium coatings on the surface of steel samples from a solution of 0.2 g/L Zr (IV) + 0.15 g/L W (VI) + 0.1 g/L Mo (VI) were a deposition temperature of 30 °C and time of 10 min. The thickness of the oxide-zirconium coatings formed under these conditions was 64.72 nm, the adhesion value was 3.17 MPa/s, and the corrosion resistance was 26 s according to Akimov’s drop method. The depth of corrosive penetration, determined in the salt fog chamber, did not exceed 2 mm after 240 h of testing, meeting the requirements for adhesive layers under the paintwork.

Corrosion behavior of AH-36 steel in seawater

In the present work, the corrosion behavior of AH-36 steel in 3% NaCl aqueous solution and natural seawater was studied using a three-electrode cell, Autolab PGSTAT 204N, and Nova 2.0 software by electrochemical methods. It has been established that after contact of the steel with chloride-containing media, the open circuit potential of steel shifts sharply to the negative region, which indicates a decrease in the corrosion resistance of steel in chloride-containing media. In seawater, the stabilization of the open circuit potential is observed within 60 min, and in NaCl solution – 120 min. The constant value of the open circuit potential of steel in seawater is in a more negative range compared to the constant value of the open circuit potential of steel in NaCl solution. In order to study the kinetics of the corrosion process of steel, polarization curves were obtained in the potentiostatic mode. It is shown that the corrosion potentials and currents of the samples decrease over time and tend to constant values. In all cases, the corrosion process in seawater occurs and stabilizes (within 20 min) faster than in NaCl solution. The anode Tafel coefficient takes a value in the range of 0.1-0.2 V, which may indicate the same mechanism of the anodic process. As a result of full-scale tests (Nha Trang, Vietnam), it can be seen that the steel samples are strongly susceptible to corrosion at the initial stage and over time the corrosion rate decreases and tends to a constant value (0.27 g/m2.h). This is due to the sample surface passivation during corrosion tests.

Theoretical Description for Anti-COVID-19 Drug Remdesivir Electrochemical Determination, Assisted by Squaraine Dye–Ag2O2 Composite

For the first time, the remdesivir anti-COVID-19 drug electrochemical determination has been evaluated theoretically. In this work, an anodic process involving the Squaraine Dye – Ag2O2 composite has been evaluated. The mechanism of the electroanalytical process is branched, which implies relatively dynamic behavior. Nevertheless, the correspondent mathematical model analysis, made by linear stability theory and bifurcation analysis, confirms the composite electroanalytical efficiency as an electrode modifier.