Insight into the covalent grafting of organic films onto carbon steel surfaces for protection

The novel use of p-nitrophenyldiazonium tetrafluoroborate salt (GG salt) as a protectant that is electrochemically grafted onto carbon steel has been investigated in 0.05 mol L^?1 H₂SO₄ and 5 wt% NaCl solutions using various corrosion monitoring techniques, such as electrochemical impedance spectroscopy, potentiodynamic polarisation, infrared spectra and scanning electron microscopy measurements. The electrochemical study reveals that this compound is a mixed inhibitor that predominantly controls the cathodic reaction. The surface-grafted film decreases the double-layer capacitance and obviously increases the charge transfer resistance relative to a bare carbon electrode. The values of inhibition effect remain nearly unchanged with an increase in temperature range of 298–318 K. The aryl diazonium is covalently bonded on the steel surface, causing a slight decrease in the apparent activation energy. Overall, the surface-grafted films exhibit excellent inhibition performance in acid and saline solutions within the studied temperature range.