Vol 61, No 4 (2025)

The effect of concentration of acetic acid ranged from 0 to 5000 ppm on the processes of initiation and propagation of pitting corrosion in martensitic class stainless steel containing 13% chromium was studied. The research was conducted in CO₂-saturated 5 wt. % sodium chloride solutions at various temperatures using electrochemical methods, including cyclic potentiodynamic polarization and pulse potentiostatic technique. The results show that the presence of acetic acid stimulates the formation and development of localized corrosion, increases the metal dissolution rate within the pits, promotes the initiation of a greater number of pits, and facilitates their spread on surface, leading to the expansion due to smaller pits adjacent to the main ones.

The distance between ions and molecules of ionic liquid in solution is estimated. It is found that in the concentration range of 1–2 mol/l, a maximum should be expected on the concentration dependence of specific electrical conductivity (EC), since contact ion pairs are formed in the solution. Specific EC of concentrated solutions of 1-butyl-4-methylpyridinium tetrafluoroborate in dimethylformamide was measured in the temperature range of 10–70°C, and the density of these solutions was measured in the temperature range of 10–60°C. The dependences of specific EC and density on temperature and concentration are analyzed. The density of solutions decreases linearly with increasing temperature, and specific EC passes through a maximum with increasing concentration. With an increase in temperature from 10 to 70°C, the concentration c_max corresponding to the maximum EC κ_max increases from 1.258 to 1.825 mol/l. To generalize the temperature and concentration dependences of the specific EC, the normalized EC κ/κ_max and normalized concentration c/c_max were used. In the coordinates κ/κ_max – c/c_max, all values of the normalized EC κ/κ_max fit on to a single curve. It is shown that at concentrations not exceeding ~1.0 mol/l, with increasing temperature, the specific EC κ increases in direct proportion to the limiting high-frequency electrical conductivity of the solvent κ_∞. Based on the analysis of the κ – κ_∞ dependencies, the solvation numbers of ionic liquid ions in dimethylformamide were determined, which decrease from 2.89 to 1.09 with an increase in concentration from ~0.1 to ~1.0 mol/l.