Investigating the effect of solution pH on speciation of La(4OH-cin)3 with correlation to electrochemical behaviour and corrosion efficiency

The nature of the species in solution plays a major role on the effectiveness of the corrosion inhibitor on a steel substrate. The speciation of lanthanum 4-hydroxy cinnamate (La(4OHCin) ₃) in solution has been evaluated using experimental techniques composed of potentiodynamic polarisation, immersion tests, nuclear magnetic spectroscopy and mass spectroscopy. It is evident that the species in solution are dependent on pH and this impacts the corrosion inhibition mechanism and the efficiency. It was found that at a neutral pH of 5.5 the La(4OH-Cin)₃ behaves as a strong anodic inhibitor. Whereas, when the pH shifts to low (pH2.5) and/or high (pH8) the corrosion mechanism changes.