Effect of addition of theobroma cacao peels extract (TCPE), a new proposed green inhibitor, on tensile and hardness properties, and related microstructure of mild steel exposed in solution of 1.5M HCl was investigated in order to know the contribution of this kind of inhibitor in controlling mechanical properties, in addition to reducing corrosion attack. Corrosion behaviors including inhibition mechanism and adsorption process during exposure were then discussed. Corrosion rate and inhibitory efficiency of mild steel samples containing 0.3%C were determined using weight loss method. The samples were exposed in the acid solution with and without addition of 0.5-2.5% the TCPE. Tensile and hardness tests were subsequently performed on the samples to determine the change of mechanical properties of the metal prior and after addition of the extracts. Sample surface morphologies and chemical composition as well were observed by a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX). The results show that the strength, hardness and elongation of mild steel drop significantly due to heavy damage in the surface after immersion in the HCl solution for 32 days. However, these mechanical properties gradually increase with increasing concentration of the extract following the increase of surface coverage and inhibition efficiency. The increase of the tensile properties and hardness is due mainly to the ability of the inhibitor to cover mild steel surface through formation of metal-organo complexes protection layer in the surface of the mild steel. Although total carbon level in the surface of the mild steel also increases significantly, there is no any proof of carbon difussion into the mild steel. The addition of polar extract of theobroma cacao peels into a solution of 1.5 M HCl is, therefore, not only effective to minimize the degradation on the mild steel surface, but it also diminishes the mechanical properties reduction of the mild steel.
Green inhibitor from Thaumatococcus daniellii Benn for corrosion mitigation of mild steel in 1M HCl
