Experimental and theoretical studies on the inhibitory potential of Lippia javanica leaf extract for aluminium corrosion in 1M HCl medium

Figures & data

Figure 1. The VBS molecule’s sugar groups (glucose and rhamnose) and two antioxidants (phenylpropanoid and phenylethanoid) linked through an ester and glycosidic linkages.

Figure 2. OCP curves obtained for the uninhibited and ALJPE-inhibited (200–800 ppm) Al sample in 1 M HCl.

Figure 3. Tafel extrapolation using EC − Lab software for the uninhibited Al sample immersed in 1 M HCl solution.

Figure 4. PDP-Tafel plots for the uninhibited and ALJPE-inhibited (200–800 ppm) Al system in 1 M HCl at 303 K.

Table 1. PDP parameters for the uninhibited and ALJPE-inhibited Al system.

Conc. of ALJPE	CR	Ecorr	βa	βc	icorr	IEPDP
(ppm)	(mpy)	(mV)	(mV.dec^−1)	(mV.dec^−1)	(μA.cm^−2)	(%)
0	2492.66	−740.497	64.6	183.6	5831.281	−
200	255.138	−744.354	13.3	127.8	594.661	89.80
400	236.015	−745.596	33.8	146.5	553.166	90.51
600	74.5641	−756.712	22.8	137.4	173.790	97.02
800	62.5649	−757.873	19.4	122.8	145.823	97.50

Figure 5. EIS-Nyquist (a) and Bode (b) plots for the uninhibited and ALJPE-inhibited (200–800 ppm) Al system in 1 M HCl at 303 K.

Figure 6. Equivalent circuit for simulating the EIS data with a focus on the uninhibited corrosive Al system (1 M HCl).

Table 2. EIS parameters for the uninhibited and ALJPE-inhibited Al system.

Conc. of ALJPE (ppm)	Rs (Ω)	CPE, Y0 (S.sec^n) ×10^–4	N	L1 (H)	Rct (Ω)	Rp (Ω.cm^2)	Cdl (μF.cm^–2) ×10^–4	RL (Ω)	IER p (%)	${\chi }^2$×10^–3
0	1.392	1.029	0.9548	10.24	6.617	0.9255	5.909	1.076	−	2.707
200	1.027	1.089	0.96	14.5	32.75	1.9814	14.167	2.109	53.29	4.27
400	4.926	1.006	0.9702	35.36	50.25	7.5305	5.937	8.858	87.71	2.481
600	7.561	0.5847	0.977	67.25	143.3	17.7197	4.028	20.22	94.78	5.006
800	1.989	1.054	0.9346	429	165.6	82.7249	1.733	165.3	98.88	4.269

Figure 7. The dependence of (a) IE(%) (solid lines) and (b) C_R (dashed lines) on the concentration of ALJPE after 7 h of immersion of Al samples in 1 M HCl at different temperatures.

Table 3. Gravimetric parameters for the uninhibited and ALJPE-inhibited Al system in 1 M HCl corrosive solution at 303–333 K.

Conc. of ALJPE (ppm)	303 K		313 K		323 K		333 K
	CR (g.cm^−2.h^−1)	IE ± SDIE (%)	CR (g.cm^−2.h^−1)	IE ± SDIE (%)	CR (g.cm^−2.h^−1)	IE ± SDIE (%)	CR (g.cm^−2.h^−1)	IE ± SDIE (%)
0	8.6931 × 10^−3	−	8.9549 × 10^−3	−	1.0930 × 10^−2	−	1.1308 × 10^−2	−
200	1.2924 × 10^−3	85.13 ± 3.5	3.3875 × 10^−3	62.17 ± 1.7	5.4723 × 10^−3	49.93 ± 3.3	8.0348 × 10^−3	28.95 ± 4.5
400	1.1265 × 10^−3	87.04 ± 2.9	3.0917 × 10^−3	65.47 ± 1.7	5.3870 × 10^−3	50.71 ± 3.1	7.6616 × 10^−3	32.25 ± 2.2
600	7.2606 × 10^−4	91.65 ± 2.5	2.9539 × 10^−3	67.01 ± 1.1	5.0490 × 10^−3	53.81 ± 1.2	7.5698 × 10^−3	33.06 ± 2.0
800	7.0499 × 10^−4	91.89 ± 5.0	2.6474 × 10^−3	70.44 ± 0.9	4.3387 × 10^−3	60.30 ± 5.9	7.5433 × 10^−3	33.29 ± 1.0

Figure 8. Variations in %IE from gravimetric analysis with immersion time for 800 ppm ALJPE at 303 K.

Figure 9. The dependence of (a) IE(%) (solid lines) and (b) C_R (dashed lines) on temperature after 7 h of immersion of Al samples in 1 M HCl at different ALJPE concentrations.

Figure 10. Arrhenius (a) and Transition (b) state diagrams for the uninhibited (blank) and ALJPE-inhibited (200–800 ppm) Al system in corrosive 1 M HCl solution.

Table 4. Gravimetric parameters for the uninhibited and ALJPE-inhibited Al system in 1 M HCl corrosive solution at 303–333 K.

Conc. of ALJPE (ppm)	Ea (kJ.mol^−1)	ΔHa* (kJ.mol^−1)	Ea − ΔHa = RT (kJ.mol^−1)	ΔSa* (kJ.mol^−1)	Qads (kJ.mol^−1) (K)
					303 – 313	313 – 323	323 – 333
0	6.5468	4.7746	1.7722	−200.8483	−	−	−
200	39.0947	36.5258	2.5689	−196.0038	−98.4324	−42.0008	−80.0554
400	39.4380	36.8731	2.5649	−195.9774	−99.7474	−51.3996	−68.9368
600	37.7821	35.1961	2.5860	−196.2460	−133.0566	−46.7402	−76.7598
800	43.6035	41.0187	2.5848	−195.3469	−122.9676	−37.8634	−99.5605

Table 5. Comparison of IE(%) for Al obtained by gravimetry in this work with literature.

ALJPE (ppm) This work	IE(%)	Bassia muricata (ppm) [91]	IE(%)	Piper longum (ppm) [92]	IE(%)	Rosemary (g/L) [93]	IE(%)	Thymus Algerians (g/L) [94]	IE(%)
200	80.63	50	55.2	50	66	0.1	62.7	0.25	36.7
400	83.45	100	61.1	100	75	0.2	76.2	0.50	60.2
600	96.25	150	66.7	200	91	0.3	82.7	0.75	78.7
800	97.22	200	71.5	300	92	0.4	91.3	1	76.6
−	−	250	79.5	400	94	0.5	95.7	−	−
−	−	300	85.9	−	−	−	−	−	−

Figure 11. Gravimetric (a), EIS, and PDP (b) Langmuir adsorption isotherms for Al system with different concentrations of ALJPE in corrosive 1 M HCl solution.

Table 6. Gravimetric, EIS, and PDP Langmuir adsorption isotherm parameters for ALJPE-inhibited Al system in 1 M HCl corrosive solution at different temperatures.

Method	T (K)	R^2	Slope	Intercept	Kads (L.g^−1)	ΔG°ads (kJ.mol^−1)
Gravimetric	303	0.9990	1.0076	0.0554	18.0505	−24.6914
	313	0.9984	1.3694	0.0556	17.9856	−25.4969
	323	0.9827	1.5485	0.1790	5.5866	−23.1716
	333	0.9998	2.8670	0.1038	9.6339	−25.3977
EIS	303	0.9755	0.7392	0.1988	5.0302	−21.4725
PDP	303	0.9984	0.9850	0.0334	29.9401	−25.9662

Table 7. The K_L values for various concentrations of ALJPE at 303 to 333 K from gravimetric Langmuir isotherm parameters.

Conc. of ALJPE (ppm)	KL
	303 K	313 K	323 K	333 K
200	0.2169	0.2175	0.4723	0.3417
400	0.1217	0.1220	0.3092	0.2060
600	0.0845	0.0848	0.2298	0.1475
800	0.0648	0.0650	0.1828	0.1148
Mean	0.1220	0.1223	0.2985	0.2025

Figure 12. Different adsorption geometries of the VBS molecules (VBS 1–4) on the Al(111) surface.

Table 8. Calculated optimized energies for stable VBS adsorption sites on Al(111) surface.

System	dAl–O (Å)	h (Å)	Eint (kcal/mol)	Ebind (kcal/mol)
VBS1/Al(111)	3.321	(Al − H) 2.879	−112.937	112.937
VBS2/Al(111)	2.590	(Al − O) 2.590	−114.620	114.620
VBS3/Al(111)	3.153	(Al − H) 3.079	−107.975	107.975
VBS4/Al(111)	3.661	(Al − H) 2.936	−109.975	109.975

d_Al–O represents the distance between the nearest oxygen atom to the Al surface, and h is the interlayer distance between the topmost atom of the Al surface and the nearest atom of the VBS molecule.

Figure 13. Possible interaction mechanism of ALJPE with the Al surface in corrosive HCl solution.

Figure 14. Contact angles for the untreated Al substrate (a), Al substrate when immersed in uninhibited (b), and ALJPE-inhibited (c) 1 M HCl medium for 7 h.

Figure 15. UV-vis spectra for 1 M HCl solution with ALJPE before immersion of Al sample (HCl + ALJPE), after immersion (HCl + ALJPE–Al³⁺), and the sample without ALJPE (HCl + Al³⁺).

Figure 16. FTIR spectra for uninhibited (Blank–Al³⁺) and ALJPE-inhibited (ALJPE–Al³⁺) Al systems and their solutions (a) and the full-scale ALJPE-inhibited (ALJPE–Al³⁺) Al system (b).

Table 9. FTIR spectral peaks and their identification for ALJPE, Blank–Al³⁺ corrosion products, and ALJPE–Al³⁺ adsorption film on Al in 1 M HCl.

ALJPE		Blank–Al^3+ corrosion products		ALJPE–Al^3+ adsorption film
Wavenumber (cm^–1)	Functional group	Wavenumber (cm^–1)	Functional group	Wavenumber (cm^–1)	Functional group
3390	O–H, N–H	3000–4000	O–H (Al2O3.×H2O)	3000 − 4000	O–H
2924	C–H	–	–	–	–
2855	C–H	2486 − 2040	H–O–H scissor bend	–	–
1702	C=O, C=C	–	–	1620	C=O, C=C^–
1603	COO^–	1600	H–O–H scissor bend	–	–
1519	=C–O–C	–	–	1496	=C–O–C
1443	S = O, C–H, C=C	–	–	1406	S=O, C–H, C=C
1360	S = O, C–F, N = O	–	–	–	–
1223	C–O, P = O, C–F, C–N	–	–	–	–
1157 − 1030	=C–O–C	1151	γ–AlO4	–	–
812 − 760	aromatic rings	–	–	900	γ–AlO4
–	–	502	γ–AlO6	502	γ–AlO6

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