Enhanced Corrosion Resistance of Carbon Steel in Hydrochloric Acid Solution by Polyoxometalate-Estertin Derivatives

The development of
acid-resistant and efficient corrosion inhibitors
is of great significance for metal protection in many industrial processes.
In this work, eight cases of sandwich-type polyoxometalate (POM)-based
inorganic–organic hybrids, namely, carboxyethyltin and transition
metal (TM) cofunctionalized tungstoantimonates and tungstobismuthates,
formulated as NaxK10–x[(SnR)2(TM­(H2O)3)2(B-β-SbW9O33)2]·mH2O and NayK10–y[(SnR)2(TM­(H2O)3)2(B-β-BiW9O33)2]·nH2O (abbreviated
as SbW9-TM-SnR and BiW9-TM-SnR; TM = Mn, Co, Ni, and Zn; m = 18, 24, 24, and 22; n = 30, 25, 20, and 21; SnR = Sn­(CH2CH2COO)) are first used as green corrosion inhibitors for 20# carbon steel in 0.5–2.0 M HCl solutions. Weight loss and
electrochemical experiments prove that the corrosion inhibition efficiency
is all above 81% for these POM-based corrosion inhibitors at 150 mg
L–1, and SbW9-Mn-SnR shows
the highest efficiency of 96.9% at 150 mg L–1 after
immersion in a 0.5 M HCl solution for 10 h. Scanning electron microscopy–energy-dispersive
X-ray spectroscopy and X-ray photoelectron spectroscopy analyses show
that these POM-based inhibitors form films on the carbon steel and
the adsorption mechanism obeys the Langmuir adsorption model. The
thermodynamic activation parameters were calculated, proving the occurrence
of both chemical and physical adsorptions. The film-forming mechanism
was also analyzed. This work provides guidance for synthesizing new
lacunary POM-based materials to protect metals from corrosion in HCl
pickling.