Effect of organic component (tartrate) addition on cerium nitrate's ability to inhibit corrosion of mild steel in NaCl solution

Cerium tartrate (CeTar), produced in this study by precipitating cerium nitrate with potassium sodium tartrate (KNaTar), was examined as a corrosion inhibitor. Weight loss tests show inhibition efficiency of 71.7 % with Ce(NO3)3 and 88.7 % with CeTar inhibitor for one-month exposure to mild steel in 7 g/L NaCl solution. The inhibition efficiency drops to 28.6 % with the former and remains around 87 % with the latter inhibitor after six months of exposure. Similar results from electrochemical testing indicate that the inhibition efficiency decreases by adding cerium nitrate. Still, the cerium tartrate inhibitor demonstrates a nearly constant inhibition efficiency for up to 30 d, i.e., ≈90 %. Electrochemical impedance spectroscopy (EIS) performed in these cases shows the following results: (i) with cerium nitrate, a film of iron and cerium oxide, which on prolonged exposure diminishes, and (ii) with cerium tartrate, the formation of a bimetallic film (Fe-tartrate-Ce) and a mixture of cerium hydroxide and iron oxide that protects steel for a longer duration. These inferences are based on the analyses of scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron (XPS), and Raman spectroscopy results.