Extreme Materials

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Quantitative and qualitative insights into the corrosion mitigation mechanism of N,N-dibutyl aniline for mild steel in sulfuric acid

Meenakshi Gupta, Mansi Y. Chaudhary, Neeta Azad, Shramila Yadav

Extreme Materials, 2025, 1(3): 44-60. DOI: 10.1016/j.exm.2025.07.001

Isotherm	Isotherm Equations	Temp. (K)	Equation	R²
Langmuir	$\mathrm{l}\mathrm{o}\mathrm{g}\frac{c}{\theta }=\mathrm{l}\mathrm{o}\mathrm{g}c-\mathrm{l}\mathrm{o}\mathrm{g}{K}_{ads}$ (eq. 8)	298	y=0.9763x+0.0023	1
		308	y=0.9761x+0.0253	1
		318	y=0.9680x+0.0200	1
		328	y=0.9675x+0.0651	0.9999
Freundlich	$\mathrm{l}\mathrm{o}\mathrm{g}\theta =\mathrm{l}\mathrm{o}\mathrm{g}{K}_{ads}+\frac{1}{n}\mathrm{l}\mathrm{o}\mathrm{g}c$ (eq. 9)	298	y=0.0237x-0.0023	0.9963
		308	y=0.0239x-0.0253	0.9430
		318	y=0.0320x-0.0200	0.9588
		328	y=0.0325x-0.0651	0.9188
Temkin	$\theta =\frac{-2.303\mathrm{l}\mathrm{o}\mathrm{g}{K}_{ads}}{2a}-\frac{2.303\mathrm{l}\mathrm{o}\mathrm{g}c}{2a}\mathrm{ }$ (eq.10)	298	y=4.4x+98.15	0.9903
		308	y=4.09x+92.66	0.9552
		318	y=5.17x+92.78	0.9676
		328	y=5.01x+84.89	0.8871
Flory-Huggins	$\mathrm{l}\mathrm{o}\mathrm{g}\frac{\theta }{c}=\mathrm{l}\mathrm{o}\mathrm{g}{K}_{FH}+{x}_{FH}\mathrm{l}\mathrm{o}\mathrm{g}(1-\theta )$ (eq. 11)	298	y=6.8517x+9.3482	0.8874
		308	y=12.501x+12.123	0.9779
		318	y=11.166x+10.501	0.9769
		328	y=10.479x+8.9185	0.8040
El-Awady	$\mathrm{l}\mathrm{o}\mathrm{g}\frac{\theta }{1-\theta }=\mathrm{l}\mathrm{o}\mathrm{g}{K}^{\text{'}}+\mathrm{y}\mathrm{l}\mathrm{o}\mathrm{g}\mathrm{c}$ (eq. 12)	298	y=0.1502x+1.2984	0.9413
		308	y=0.1003x+0.9398	0.9753
		318	y=0.1168x+0.9144	0.9790
		328	y=0.1071x+0.7213	0.8473
Frumkin	$\mathrm{l}\mathrm{n}\frac{\theta }{(1-\theta )c}=\mathrm{l}\mathrm{n}{K}_{ads}+2a\theta \mathrm{ }$ (eq. 13)	298	y=-43.807x+46.103	0.9771
		308	y=-48.207x+47.232	0.9480
		318	y=-37.939x+37.595	0.9610
		328	y=-35.748x+33.068	0.8531

Table 4 Analysis of adsorption behavior using different isotherm models.

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Fig. 1. Structure of N, N Dibutyl aniline (NNDBA).
Table 1 Temperature and concentration dependent corrosion rate and inhibition efficiency of mild steel in H₂SO₄ medium in the presence and absence of NNDBA determined via gravimetric method.
Fig. 2. Effect of NNDBA concentration on corrosion protection performance of mild steel at all studied temperatures.
Table 2 Time-dependent mass depletion data for mild steel corrosion in H₂SO₄ solution.
Fig. 3. Time-dependent corrosion behavior of mild steel in H₂SO₄.
Fig. 4. Temperature dependence of corrosion rate: logC_r vs. 1/T for mild steel in H₂SO₄ medium in the presence and absence of NNDBA.
Table 3 Energy of activation (E_a ) for mild steel corrosion in H₂SO₄ medium in the presence and absence of NNDBA.
Fig. 5. Different adsorption isotherms for mild steel in H₂SO₄ medium in the presence and absence of NNDBA (a) Langmuir, (b) Freundlich, (c) Temkin, (d) ElAwady, (e) Flory-Huggins, and (f) Frumkin adsorption isotherm.
Table 5 Thermodynamic insights from the Langmuir adsorption isotherm at all studied temperatures.
Fig. 6. Temperature dependence of adsorption equilibrium constant: logK_adsvs.1/T.
Fig. 7. Cathodic and anodic polarization run via PDP studies for various concentrations of H₂SO₄ in the presence and absence of NNDBA at 298 K.
Table 6 Corrosion current and inhibition efficiency for mild steel in H₂SO₄ medium in the presence and absence of NNDBA determined via PDP studies at 298 K.
Fig. 8. Bode plot of mild steel in H₂SO₄ and in 10^-1M NNDBA at 298 K.
Fig. 9. Nyquist plot of mild steel in H₂SO₄ and in 10^-1 M NNDBA at 298 K.
Fig. 10. Equivalent Circuit.
Table 7 Electrochemical Impedance parameters for mild steel in H₂SO₄ medium in the presence and absence of NNDBA at 298 K.
Fig. 11. Scanning electron micrograph of mild steel in (a) 0.5H₂SO₄ (b) 10^-1 M NNDBA in H₂SO₄ (c) 10^-7 M NNDBA in H₂SO₄ at 3000 magnifications.
Fig. 12. AFM of (a) plain mild steel specimen, (b) mild steel specimen in the 0.5H₂SO₄ solution (c) mild steel specimen in presence of 10^-1MNNDBAⁱⁿH₂SO₄.
Fig. 13. Optimized geometry of NNDBA with HOMO and LUMO distributions and their corresponding energy levels.
Fig. 14. Optimized geometry of protonated NNDBA with HOMO and LUMO distributions and their corresponding energy levels.
Table 8 Fukui functions (f^*,f, and f² ) for atoms of NNDBA.
Fig. 15. Bar graph representing the Fukui functions (f^*,f, and f² ) for individual atoms of NNDBA.
Table 9 Outputs calculated by the Monte Carlo simulation for adsorption of NNDBA, on Fe (110).
Fig. 16. MD simulation captures in (a) top view of adsorbed NNDBA molecule on mild steel surface (b) front view of interactions between NNDBA and mild steel (c) top view of adsorbed NNDBA molecule on mild steel in presence of H₂O and H₂SO₄ (d) top view of adsorbed NNDBA molecule on mild steel in presence of H₂O and H₂SO₄.
Table 10 Comparative Overview of NNDBA and Structurally Related Corrosion Inhibitors.
Fig. 17. Visualization of interaction between NNDBA and mild steel (MS) surface.

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