Protection of Aluminium Metal in 0.5 M HCl Environment by Mature Arecanut Seed Extracts: A Comparative Study by Chemical, Electrochemical and Surface Probe Screening Techniques

The corrosion inhibition behaviour of ethyl acetate extract from mature arecanut seed (EEMAS) and water extract from mature arecanut seed (WEMAS) on aluminium in 0.5 M hydrochloric acid (HCl) environment was thoroughly investigated by employing gravimetric (weight loss), electrochemical (Tafel plot and AC impedance) and surface probe (SEAM and AFM) techniques. From the gravimetric technique, it was observed that, the superior inhibition property was ensured at the concentration of 12 g l(-1) of plant extracts. The chemical or physical nature of the film formed by plant extracts (both EEMAS and WEMAS) was further inspected based on kinetic and thermodynamic parameters. According to Tafel plot studies, the corrosion current value decreases appreciably with an increase in the plant product concentration, which is an indication of the reduction in the corrosion rate. An increase in the charge transfer resistance values with the addition of plant extract constituents to the corrosive medium was clearly observed from AC impedance spectroscopy technique. Surface characterisation of target metals by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques as a function of contact time in a corrosive medium (0.5 M HCl) noticeably gives clue about the protective role of plant extracts on the metal (aluminium) surface. The order of protection efficiency obtained from all techniques was found to be WEMAS > EEMAS.