Adsorption Effect of Theobroma Cacao Extract On Steel Surface to Protect Corrosion Rate

Abstract

Research has been carried out to slow down the corrosion rate of steel by using biomass waste inhibitors of cocoa pod extract (Theobroma cacao). The steel is pre-soaked in the inhibitor for 24, 72, 120, and 168 hours. Then followed by immersion in corrosive HCl media with variations of time, namely 48, 96, and 144 hours. Characterization of corrosion rate by weight loss method, surface morphology by optical microscopy, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). Phase analysis that occurs with X-Ray Diffraction (XRD), and the Density Functional Theory (DFT) method to analyze the shape of the molecular structure, geometry, HOMO and LUMO contours. The weight loss method gives the best results with the lowest corrosion rate of 0.2972 mg.cm2/hour and an inhibition efficiency of 74.7128% for steel soaked in inhibitor for 168 hours and in HCl for 48 hours. Morphological analysis using optical microscopy and SEM showed that the longer it was immersed in the inhibitor, the flatter the surface and the fewer cracks it had. The XRD results also showed that there were four sharp peaks of the crystalline Fe and C phases due to the reaction between the steel surface and the inhibitor. AFM analysis shows that the adsorption formed on the surface is directly proportional to the length of immersion in the inhibitor. Analysis of the DFT method shows that the greater the EHOMO, the easier it is for a molecule to donate its electrons, so that the greater its ability to protect against corrosion. Optimization and calculation of tannin compounds that react with the steel surface resulted in a fairly high inhibition efficiency of the cocoa pod extract inhibitor, which was 80.2098%.