Experimental and theoretical study on the corrosion inhibition of mild steel by nonanedioic acid derivative in hydrochloric acid solution

Abstract

The corrosion performance of mild steel (MS) in 1M HCl solution was examined by weight loss (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), and open circuit potential (OCP) measurements in the absence and presence of nonanedihydrazide. PDP measurements indicated that nonanedihydrazide acts as a mixed inhibitor due to its adsorption on the MS surface, exhibiting an inhibition efficiency of more than 97%. The surface morphology investigation of the protective layer on the MS surface confirmed that adsorption of nonanedihydrazide molecules occurred via chemical adsorption following Langmuir's isotherm model. The effect of temperature on the corrosion performance in the presence of nonanedihydrazide was investigated in the range of 303-333 K, showing that the inhibition efficiency increased with an increase in the inhibitor concentration and decreased with an increase in temperature. A new green corrosion inhibitor was synthesised and theoretical computations were conducted to completely understand the inhibition mechanism. Nonanedihydrazide molecules were investigated by DFT (density functional theory) using the B3LYP functional to evaluate the relationship of corrosion inhibition performance and the molecular structure. The computed theoretical parameters presented significant support for understanding the inhibitive mechanism revealed by the inhibitory molecules and are in good agreement with WL, PDP, EIS, (EFM), and OCP results.

Figure 1

Schematic route for the synthesis of nonanedihydrazide.

Figure 2

(a) FTIR; (b) Proton NMR; (c) Carbon-¹³ NMR and (d) Mass spectra of nonanedihydrazide.

Figure 3

Corrosion rate and inhibition efficiency for MS in 1 M HCl at different immersion times and nonanedihydrazide concentrations.

Figure 4

Effect of temperature and concentration on the inhibition efficiency of nonanedihydrazide on MS in 1 M HCl.

Figure 5

Arrhenius plot $log{C}_{R}vs\frac{1}{T}$ of nonanedihydrazide optimised concentration (0.5 mM) for 5 h.

Figure 6

Langmuir adsorption model plot for nonanedihydrazide.

Figure 7

OCP as a function of the nonanedihydrazide concentration for MS in 1.0 M HCl at 303 K.

Figure 8

OCP as a function of temperature for MS in 1.0 M HCl and 0.5 mM nonanedihydrazide.

Figure 9

Nyquist plots for MS in 1.0 M HCl with various concentrations of nonanedihydrazide at 303 K.

Figure 10

Nyquist plots for MS in 1.0 M HCl with 0.5 mM nonanedihydrazide at various temperatures.

Figure 11

Equivalent circuit model utilised to fit impedance data in 1.0 M HCl with and without the addition of nonanedihydrazide.

Figure 12

Experimental impedance and phase data in Bode format for MS in 1.0 M HCl containing 0.5 mM nonanedihydrazide denotes the fitted line using the equivalent circuit.

Figure 13

Potentiodynamic polarization curves for MS in 1.0 M HCl with different concentrations of nonanedihydrazide at 303 K.

Figure 14

Potentiodynamic polarization curves for MS in 1.0 M HCl with 0.5 mM nonanedihydrazide at various temperatures.

Figure 15

MS intermodulation spectrum in 1 M hydrochloric acid solution with (a) 0.05, (b) 0.1, (c) 0.2, (d) 0.4 and (e) 0.5 mM nonanedihydrazide at 303 K.

Figure 16

Inhibitor energy diagram HOMO and LUMO energies.

Figure 17

Fukui functions of the studied inhibitor.

Figure 18

Proposed protection mechanism for MS by the inhibitor via chemical and physical adsorption processes.