Some thermodynamic and kinetic properties of H2SO4–H3PO4–H2O–Fe(III) system

The values of the electrode potentials of the redox couple Fe(III) / Fe(II) and the half-wave potentials of the reactions Fe3+ + e– = Fe2+ и Fe2+ — e– = Fe3+ on the cyclic voltammogram of a platinum electrode in acid solutions containing Fe(III) salts have been measured to characterize the oxidizing ability of the H2SO4—H3PO4—H2O—Fe(III) system. The values of these experimentally obtained parameters are close. A decrease in the oxidizing ability of H2SO4 and H3PO4 mixtures containing Fe(III) with an increase in the molar fraction of H3PO4 in them occurs due to the formation of Fe(III) complexes with phosphate anions which are inferior to their hydrate and sulfate complexes in the oxidizing ability. The temperature coefficients of the electrode potential (dE / dt) of the redox couple Fe(III) / Fe(II) in the H2SO4—H2O, H2SO4—H3PO4—H2O and H3PO4–H2O systems were determined experimentally. The diffusion coefficients of Fe(III) in the studied solutions were calculated based on the Randles—Shevchik equation. The temperature dependence of the diffusion coefficients of Fe(III) cations is satisfactorily described by the Arrhenius equation. The parameters of this equation are calculated.

On increase in stability of superhydrophobic oleic acid layers on surface of D16 aluminum alloy

The possibility of increasing the stability of SHP layers formed from ethanol solutions of oleic acid (OlA) by layer-by-layer modification of the laser-textured surface of the alloy D16 by ethanol solutions of trialkoxysilanes (vinyltrimethoxysilane (VS), octyltriethoxysilane (OTES)) is discussed. It is shown that OTES is more effective than VS in achieving the SHF state of the alloy surface. The protective ability of the coatings was evaluated by polarization measurements in 0,05 M NaCl water solution and corrosion tests in a salt spray chamber. It is shown that the two-stage modification of the alloy surface in solutions of OTES and OlA at Cin = 10 mmol / l, allows one to surpass the protective capacity of individual components, and τcor = 498 h. It is important that the SHP properties of the coating are preserved for 240 hours of testing under salt spray chamber conditions.