Mild steel used in a wide range of industries easily develops rust and the corrosion causes huge economic loss every year. As chemical corrosion inhibitors are detrimental to the environment, there is an urgent need to develop green inhibitors. Now, researchers from Indian Institute of Technology (BHU), Varanasi, have successfully produced a chitosan-based corrosion inhibitor that shows over 90% efficiency.
Chitosan
Chitosan is a natural polysaccharide found in the shell of crab, shrimp and also in the cell wall of fungi. “As the solubility of chitosan in water is poor, polyethylene glycol (PEG) was incorporated to it and a novel PEG-crosslinked chitosan was developed. PEG is non-toxic and has been approved by the FDA even for internal consumption,” says Vandana Srivastava from the Department of Chemistry of the institute and first author of the paper published in ChemistrySelect.
Mild steel was immersed in a corrosion-inducing solution of hydrochloric acid containing different concentration of chitosan-PEG ranging from 50-200 mg/L for six hours. The novel inhibitor was found to form a thin film on the metal surface.
“We studied the precise chemical mechanisms and found that the inhibitor is adsorbed as a thin film on the steel surface. The inhibitor blocks the active sites on steel available for corrosion thereby mitigating corrosion,” explains M.A. Quraishi from the institute and corresponding author of the work.
Weight loss studies and electron microscopy imaging showed that a maximum inhibition of 93.9% was achieved when the concentration of the treated solution was 200 mg/L.
Smooth surface
“Usually when steel is treated with anti-corrosive agents there is a change in its surface and it tends to get rough. But our inhibitor did not alter the surface. In fact, there was a significant improvement in the surface smoothness,” Prof. Quraishi adds. “The shells of the shrimps are usually discarded as waste and if we can use them and develop such eco-friendly products it will be a good way to convert waste material to a useful application.”
