The Effect of 10-Methylacridinium and Potassium Iodides on the Salt Passivation of Copper and α-Brass in Chloride Solution

A comparative study of potassium and 10-methylacridinium iodides as inhibitors of copper and -brass anodic dissolution depending on the potential, rotational speed of disk electrode, and concentration of additives is performed. The effect of additives on the film formation at the metal surface is determined.     

Catalytic Sulfation of Betulin with Sulfamic Acid: Experiment and DFT Calculation

Betulin is an important triterpenoid substance isolated from birch bark, which, together with its sulfates, exhibits important bioactive properties. We report on a newly developed method of betulin sulfation with sulfamic acid in pyridine in the presence of an Amberlyst^®15 solid acid catalyst. It has been shown that this catalyst remains stable when being repeatedly (up to four cycles) used and ensures obtaining of sulfated betulin with a sulfur content of ~10%. The introduction of the sulfate group into the betulin molecule has been proven by Fourier-transform infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopy. The Fourier-transform infrared (FTIR) spectra contain absorption bands at 1249 and 835–841 cm⁻¹; in the UV spectra, the peak intensity decreases; and, in the nuclear magnetic resonance (NMR) spectra, of betulin disulfate, carbons С3 and С28 are completely shifted to the weak-field region (to 88.21 and 67.32 ppm, respectively) with respect to betulin. Using the potentiometric titration method, the product of acidity constants K₁ and K₂ of a solution of the betulin disulfate H⁺ form has been found to be 3.86 × 10^–6 ± 0.004. It has been demonstrated by the thermal analysis that betulin and the betulin disulfate sodium salt are stable at temperatures of up to 240 and 220 °C, respectively. The density functional theory method has been used to obtain data on the most stable conformations, molecular electrostatic potential, frontier molecular orbitals, and mulliken atomic charges of betulin and betulin disulfate and to calculate the spectral characteristics of initial and sulfated betulin, which agree well with the experimental data.     

Anodic dissolution and passivation of lead in sodium sulfate solutions

The anodic behavior of lead depending on the sulfate solution concentration is studied. The relation between oxide-hydroxide passivation and salt repassivation is found. The main characteristics of the forward and reverse branches of the polarization curves and cyclic voltammograms, as well as anodic chronoammograms and cathodic chronopotentiograms, are determined. The time dependence of the phase-formation current is constructed and analyzed.     

Corrosion electrochemical behavior of tin-cadmium alloys in a sulfate solution

The behavior of preeutectic (by cadmium) and eutectic tin-cadmium alloys is studied compared to pure metals. The dependence of main characteristics of direct- and reverse-run polarization curves on the alloy composition is established. Information is obtained on the ratio between inhibiting and promoting adsorption of benzotriazole and potassium oleate, depending on the potential, dissolution character, and alloy composition. To compare the results of work [1], the corrosion-electrochemical behavior of tin-cadmium alloys in a sulfate solution was studied, depending on their composition and potential E and also the effect of benzimidazole (BI) and potassium oleate (PO) on it.     

Dissolution of Ni-Zn alloys in sulfate solutions

The anodic behavior of nickel, zinc, and their alloys with the zinc content from 30 to 90% in blank sulfate solutions and in the presence of quinolinium perchlorate derivatives is studied. For the mixed dissolution kinetics, the effect of additives in the stages of ionization and liquid- and solid-phase diffusion is elucidated. The inhibition coefficients of the process are shown to correlate with hydrophobicity constants of alkyl substituents in organic cations.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 208–217.Original Russian Text Copyright © 2005 by Ekilik, Berezhnaya, Tugolukova.     

Mutual influence of portions of simple and binary inhibitors in the acid corrosion of iron

The effects of inhibitors as power functions of their concentrations were examined analytically and graphically. The mutual influence of their portions of the was estimated. The behavior of the inhibitors in solutions of H₂SO₄ and HClO₄ was compared. The mechanism of the corrosion inhibition was proposed. It was found that the additives influence each other in the inhibition of iron dissolution and hydrogen depolarization. Original Russian Text ? V.V. Ekilik, G.N. Ekilik, A.G. Berezhnaya, E.N. Balakshina, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 645–649.     

Anodic behavior of bismuth in chloride solution

Passivation and depassivation of bismuth in 0.1 M sodium chloride solution are studied taking into account the pH value of the layer near the electrode and the composition of the film formed, which depend on the polarization. Thermodynamic and kinetic analysis of the possible passivation-depassivation mechanisms is given.     

Stability of bioactive hydroxyapatite films on titanium substrates in physiological buffer solutions

Hydroxyapatite/titanium (HA/Ti) structures heat-treated and then incubated in CaCl₂ (3 mM Ca²⁺) and KH₂PO₄ + Na₂HPO₄ (20 mM; pH 6, 7, 8) solutions have been characterized by X-ray diffraction, X-ray microanalysis, scanning electron microscopy, and pX measurements. The insoluble phases CaTiO₃ and CaTi₄O₉ have been identified. After prolonged incubation (96 h), the heat-treated structures were found to be biologically resistant. Thermostating the structures in the physiological buffer solutions studied does not rupture the bioactive film, and the HA/Ti structure is stable in such solutions.