Inhition of corrosion by glycerol stearate on selected metals

Thesis (Ph.D. (Chemistry)) -- University of Limpopo, 2023

Using “gravimetric analysis, potentiodynamic polarisation (PDP), and electrochemical impedance spectroscopy (EIS), an investigation into the corrosion prevention properties of the metals aluminium (Al), mild steel (MS), and zinc (Zn) was carried out in a solution of hydrochloric acid (HCl) with a concentration of 1. 0 M. Inhibition was shown to be more effective as the concentration of the inhibitor increased, according to the measurements from the gravimetric analysis. Glycerol stearate (GS), was investigated for its possible use as a corrosion inhibitor on aluminium, mild steel and zinc metal in 1.0 M HCl solution. Techniques such as gravimetric analysis, potentiodynamic polarisation (PDP), and impedance spectroscopy (EIS) were utilised in order to ascertain the rate of corrosion. At a concentration of 50 mol. L-1, electrochemical tests (PDP and EIS) have indicated that there is the highest percentage of inhibitory efficiency of glycerol stearate such as 81.06 % (PDP), 86.18 % (EIS) for aluminium, 82.69 % (PDP), 75.44 % (EIS) for mild steel and 71.05 % (PDP), 89.50 % (EIS) for zinc metal. It was discovered using gravimetric analysis and electrochemical techniques that the rate of corrosion decreased as the inhibitor concentration increased. The findings that glycerol stearate operated as a mixed type of corrosion inhibitor were demonstrated by the disparities that existed between the corrosion potential (Ecorr) values of the blank (1. 0 M) and inhibitor (GS) concentrations for all metals. Studies on potentiodynamic polarisation demonstrated that the addition of GS reduced the corrosion current densities on aluminium metal, mild steel, and zinc metal, which resulted in the metals being more resistant to corrosion. Using electrochemical impedance spectroscopy, the researchers found that the charge transfer resistance increased as GS concentration increased. The values of the free Gibbs energy showed that a spontaneous corrosion process was occurring at the surface of the aluminium, mild steel, and zinc metal. The Langmuir adsorption isotherm was followed by the data collected from adsorption isotherm research for each element. The presence of the adsorption coating was validated by Fourier transform infrared spectroscopy (FTIR), which was performed on the surfaces of aluminium, mild steel, and zinc. The adsorption mechanism has been further explained by using thermodynamics and quantum chemistry parameters, both of which have been calculated and interpreted. Images obtained using scanning electron microscopy (SEM) revealed that the presence of glycerol stearate significantly reduced the amount of inhomogeneity in aluminium, mild steel, and zinc.