Anticorrosive Behavior of Propolis as A Green Corrosion Inhibitor for Aluminum

Propolis, which contained polyphenol as an anticorrosive agent, is proposed as an alternative green corrosion inhibitor for Al. The inhibitor efficiency was evaluated by conducting a weight loss test in 3.5 wt.% NaCl solution on a commercially pure Al coupon. At neutral pH, in the absence of propolis, Al surface underwent uniform corrosion. Propolis with the concentrations of 400 and 800 ppm effectively inhibited corrosion reaction on Al surface with efficiency 99.9 % for up to 8 days immersion. The efficiency decreased slightly between 80-90 % with prolonging immersion time. Pits were detected on the surface as a result of corrosion. At high concentration of 1200 ppm, the inhibition efficiency was somewhat lower, below 60 %. The viscous propolis was probably agglomerated when presented at a high concentration. The inhibition mechanism was likely to involve adsorption of the propolis on the metal surface, forming a thin layer. In an acid environment, the inhibition efficiency dropped down below 40 %. Propolis was believed to release hydrogen ion that contributed to lowering the surrounding pH and increased the danger of corrosion. Nevertheless, the high inhibition efficiency of propolis, especially at the neutral environment, shows promise as a green corrosion inhibitor for Al.