engleski

Sinapinic acid as inhibitor of Al-Mg alloy corrosion in chloride solution

Increasing awareness of health and ecological risks have provided an incentive for research into the possibility of inhibition of corrosion by means of compounds isolated from plant materials, e.g. from rosemary (Rosmarinus officinalis L.)(1, 2). This study examined the possibility of inhibition of corrosion of the Al-2.5Mg alloy in deaerated 0.5 mol dm-3 NaCl solution at different temperatures (25 – 55  C), by means of sinapinic acid (3, 5-dimetoxy-4-hydroxycinammic acid). Sinapinic acid is phenolic acid also isolated from rosemary leaves. The mesurements were performed in the conventional three - electrode cell. The additive was added in concentrations 1 × 10^-5 and 1 × 10^-4 mol dm^-3 to the basic solution. Potentiodynamic polarisation curves were produced with scanning rate of 2 mV s^-1, in potential range of E = Ecorr  150 mV. The least squares method was used to extrapolate Tafel streight lines and determine the electrochemical parameters. Polarisation resistance measurements were conducted in potential range of E = Ecorr  20 mV with scan rate of 0.2 mV s^-1. The results obtained suggests that sinapinic acid acts as effective corrosion inhibitor but its efficiency decreases with the increase of temperature. The inhibitory action could be explained by the formation of complexes in the form of chelates between phenolic acids and metallic ions(2). In this way sinapinic acid readily donates a hydrogen atom (H^+ + e-), thereby creating free phenoxy radicals, which form chelates together with Al3+ ions present in the solution. The chelates formed later precipitate on the surface of the metal, inhibiting its corrosion.

Al-Mg alloy; corrosion inhibition; sinapinic acid

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