Rare earth element (REE) ß-diketone complexes as novel corrosion inhibitors for mild steel and stainless steels in a corrosive chloride media
Lawal, Olatunde Johnson
Currently, chromate compounds are among the most common chemicals used as corrosion inhibitors for different metals and alloys. However, these compounds are highly toxic and carcinogenic, and their application produces serious environmental hazards and toxicity to humans. As a result, novel green rare earth element (REE) -diketone complexes were proposed as alternatives to chromate inhibitors. Therefore, the research aim was to synthesise, characterise and study the inhibition potential of the synthesised REE -diketone complexes as a green corrosion inhibitors for mild steel and austenitic stainless steels (304 and 316 SS) in a corrosive chloride media at different temperatures. The synthesised complexes were characterised using melting point analysis, infrared spectroscopy, Raman spectroscopy, mass spectroscopy, and X-ray diffraction. Four REE β-diketone complexes of cerium and lanthanum acetylacetone and hexafluoroacetylacetone were selected for the investigation as potential corrosion inhibitors for mild steel and austenitic stainless steel using 3.5% NaCl and 0.1 M HCl solutions as corrosive chloride media. Their inhibiting potentials were assessed using weight loss tests and potentiodynamic polarisation scans. Surface analyses using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (RS) were used to investigate the steel samples after weight loss and electrochemical tests for possible oxide film layer formation on the surface of the steel. SEM and Raman spectroscopy confirmed the formation of protective films of the tested inhibitors on the steel surfaces.
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2022