Adsorption and inhibitive properties of ethanol extract of Garcinia kola and Cola nitida for the corrosion of mild steel in H2SO4

Purpose - The purpose of this paper is to study the inhibitive and adsorption characteristics of ethanol extract of Garcinia kola and Cola nitida for the corrosion of mild steel in H2SO4 solutions. Design/methodology/approach - The inhibition efficiencies were evaluated using weight loss and thermometric methods while the adsorption properties were studied using IR spectroscopy. Findings - The inhibition efficiencies of ethanol extracts of Garcinia kola and Cola nitida were comparable and vary with concentration of the extract, period of immersion and with temperature. The extracts act as adsorption inhibitors because of its phytochemical composition. The extracts are adsorbed spontaneously on the surface of mild steel according to Langmuir adsorption isotherms. The mechanism of physical adsorption is proposed from the trend of the inhibition efficiency with temperature and the values of activation energy and some thermodynamic parameters obtained. Research limitations/implications - The study provides information on the use of ethanol extract of Garcinia kola and Cola nitida as corrosion inhibitors for mild steel. Electrochemical studies such as polarisation and AC impedance spectra will illuminate the mechanistic aspects of the extract. Practical implications - Ethanol extract of Garcinia kola and Cola nitida are environmentally friendly inhibitors for the corrosion of mild steel in H2SO4. Originality/value These environmentally friendly inhibitors may find possible applications in metal surface anodising and surface coatings.