Sinapis alba extract as green corrosion inhibitor for aluminum in alkaline media

The inhibition effect of sinapis alba (SA) extract on the corrosion of aluminum in 1.0M sodium hydroxide (NaOH) was investigated using weight-loss measurements, and electrochemical polarization methods; also, surface morphology was analyzed by scanning electron microscopy (SEM) technique. The results show that sinapis alba extract is a good inhibitor, and the inhibition efficiency increases with inhibitor (sinapis alba extract) concentration, and slightly increases with increasing temperature. The inhibition efficiency reaches a maximum value of 97.98% with the highest extract concentration at 50°. In the presence of sinapis alba extract, the results were indicative of slightly decreased aluminum dissolution with increasing temperature. The adsorption of sinapis alba extract on aluminum surface obeys Langmuir adsorption isotherm, with high regression coefficient value. The entropy (ΔS^#) and enthalpy (ΔH^#) of activation are calculated and discussed. The thermodynamic adsorption free energy (ΔG^°_ads) value and sign were indicative of the physisorption of sinapis alba extract molecules on aluminum surface. Electrochemical polarization studies showed that sinapis alba extract acts as mixed type inhibitor. The results reveal that sinapis alba extract provided a very good protection to aluminum against corrosion in alkaline media. SEM results confirmed the existence of an absorbed protective film on the aluminum surface.