Experimental and computational chemistry studies on the inhibition of aluminium and mild steel in 0.1 M HCl by 3-nitrobenzoic acid

Figures & data

Figure 1. Variation of weight loss with time for the corrosion of mild steel in 0.1 M HCl containing various concentrations of NBA at 303, 313, 323 and 333 K.

Figure 2. Variation of weight loss with time for the corrosion of aluminium in 0.1 M HCl containing various concentrations of NBA at 303, 313, 323 and 333 K.

Table 1. Inhibition efficiency of NBA (from weight loss and thermometric measurements) and corrosion rate of mild steel and aluminium metals.

	%IE		CR (gh^−1cm^−2)
System	Mild steel	Al	Mild steel	Al
0.1 M HCl at 303 K		–	0.003421	0.003554
0.002 M NBA + 0.1 M HCl at 303 K	66.11 (71.02)	62.12 (71.68)	0.000100	0.000134
0.004 M NBA + 0.1 M HCl at 303 K	72.46 (79.07)	66.66 (73.32)	0.000094	0.000117
0.006 M NBA + 0.1 M HCl at 303 K	80.33 (82.03)	68.85 (78.35)	0.000081	0.000113
0.008 M NBA + 0.1 M HCl at 303 K	84.66 (86.03)	72.61 (80.66)	0.000060	0.000097
0.010 M NBA + 0.1 M HCl at 303 K	89.97 (90.35)	73.55 (82.23)	0.000023	0.000094
0.1 M HCl at 313 K			0.005071	0.005222
0.002 M NBA + 0.1 M HCl at 313K	62.54	47.25	0.000170	0.000229
0.004 M NBA + 0.1 M HCl at 313K	65.45	45.78	0.000152	0.000208
0.006 M NBA + 0.1 M HCl at 313K	68.85	54.10	0.000143	0.000186
0.008 M NBA + 0.1 M HCl at 313K	77.40	58.59	0.000107	0.000173
0.010 M NBA + 0.1 M HCl at 313K	81.25	62.64	0.000056	0.000159
0.1 HCl at 323 K			0.008952	0.010423
0.002 M NBA + 0.1M HCl at 323 K	54.86	38.80	0.000153	0.000625
0.004 M NBA + 0.1M HCl at 323 K	60.50	40.94	0.000137	0.000613
0.006 M NBA + 0.1M HCl at 323 K	65.54	41.65	0.000126	0.000611
0.008 M NBA + 0.1M HCl at 323 K	70.57	42.05	0.000111	0.000600
0.010 M NBA + 0.1M HCl at 323 K	73.85	47.24	0.000100	0.000563
0.1 M HCl at 333 K			0.014632	0.0016863
0.002 M NBA + 0.1 M HCl at 333 K	49.96	26.84	0.000190	0.001233
0.004 M NBA + 0.1 M HCl at 333 K	53.33	31.20	0.000178	0.001177
0.006 M NBA + 0.1 M HCl at 333 K	57.04	33.25	0.000162	0.001144
0.008 M NBA + 0.1 M HCl at 333 K	62.58	35.55	0.000150	0.001094
0.010 M NBA + 0.1 M HCl at 333 K	66.00	44.87	0.000132	0.000919

Note: Values in parenthesis are from thermometric experiments.

Table 2. Linear and potentiodynamic polarization parameters for the corrosion of aluminium and mild steel in the absence and presence of NBA at 303 K.

		LPR		PDP
Metal	C (M)	Rp (Ω cm^−2)	% I	βa mVdec^−1	βc mVdec^−1	Ecorr (mV)	Icorr (μA)	I %
Mild steel	Blank	27.66	–	126.6	136.4	−496	132.05	–
	0.001	104.11	73.43	117.6	123.0	−548	23.75	82.01
	0.010	218.22	87.32	114.1	118.5	−549	16.00	87.88
	0.015	535.88	94.83	106.5	110.3	−551	13.01	94.69
Aluminium	Blank	22.32	–	124.1	129.2	−455	98.22	–
	0.001	83.28	73.20	106.4	108.3	−504	37.85	61.46
	0.010	178.36	87.49	101.4	103.2	−516	17.23	82.46
	0.015	380.08	94.13	100.0	102.4	−534	14.06	85.69

Figure 3. Potentiodynamic polarization curves for the corrosion of (a) mild steel (b) aluminium in 0.1 MHCl in the absence and presence of different concentrations of NBA.

Figure 4. Arrhenius plots for the corrosion of mild steel and aluminium in 0.1 M HCl containing various concentrations of NBA.

Table 3. Arrhenius and Transition state parameters for the adsorption of NBA on aluminium and mild steel surfaces.

		Arrhenius parameters		Transition state parameters
Metal	C (M)	$E_a\left(\text{Jmo}{\text{l}}^{-1}\right)$	R^2	$\mathrm{\Delta }{H}_{\mathrm{ads}}\left(\text{Jmo}{\text{l}}^{-1}\right)$	$\mathrm{\Delta }{S}_{\mathrm{ads}}\left(\text{Jmo}{\text{l}}^{-1}\right)$	R^2
Mild steel	Blank	44.73	0.9737	38.36	−2.40	0.9947
	0.002	63.70	0.9877	15.15	−3.93	0.9999
	0.004	66.57	0.9861	14.78	−3.96	0.9892
	0.006	67.59	0.9756	16.47	−3.89	0.9984
	0.008	70.77	0.9769	22.80	−3.63	1.0000
	0.010	75.69	0.9662	33.07	−3.19	0.9544
Aluminium	Blank	40.97	0.9954	42.07	−2.22	0.9702
	0.002	17.77	1.0000	61.08	−1.71	0.9866
	0.004	17.40	0.9925	63.95	−1.59	0.985
	0.006	19.09	0.9989	65.01	−1.55	0.9736
	0.008	23.16	0.8823	68.15	−1.41	0.9751
	0.010	35.64	0.9602	64.76	−1.58	0.9635

Figure 5. Transition state plots for the corrosion of mild steel and aluminium in 0.1 M HCl containing various concentrations of NBA.

Table 4. Langmuir and Frumkin parameters for the adsorption of NBA on mild steel and aluminium surfaces.

		Langmuir				Frumkin
Metal	T (K)	Slope	lnkads	ΔGads (kJ/mol)	R^2	Slope	α	R^2
Mild steel	303	0.8080	0.7640	−12.04	0.9989	12.835	6.42	0.9967
	313	0.8368	0.5117	−11.78	0.9945	6.5611	3.28	0.9971
	323	0.8137	0.5441	−12.25	0.9992	5.8528	2.93	0.9943
	333	0.827	0.3560	−12.11	0.9970	5.9322	3.00	0.9981
Aluminium	303	0.893	0.1862	−10.59	0.9998	18.188	9.09	0.9909
	313	0.8121	0.3581	−11.38	0.9853	4.9077	2.45	0.9927
	323	0.9018	−0.3502	−9.85	0.9960	7.6661	3.83	0.9080
	333	0.7239	0.3679	−12.14	0.9775	5.4580	2.73	0.9990

Figure 6. Langmuir isotherm for the adsorption of NBA on mild steel and aluminium surfaces.

Table 5. Frequencies and peak of FTIR absorption by NBA and the corrosion product of mild steel and aluminium in the presence of NBA.

NBA before adsorption		Corrosion product of aluminium		Corrosion product of mild steel
Frequency (cm^−1)	Intensity	Frequency (cm^−1)	Intensity	Frequency (cm^−1)	Intensity	Functional group/assignment
741	27.846	745	26.176	741	5.894	OH bend
				855	13.115	N–H wag
981	60.066	978	42.856	988	8.094	=C–H bend
1072	16.272	1071	17.885			C–O stretch
1128	13.530	1131	17.00			C–N stretch
		1241	15.216			C–O stretch
1298	12.835	1288	15.992			N–O symmetric stretch in nitro
1372	39.619	1382	24.904			C–H rock
1454	26.111	1451	24.739	1456	5.351	C–C stretch in ring
1589	59.932	1590	46.413	1580	6.655	C–C stretch in ring
		1704	15.317			C = O stretch
1746	14.322	1739	14.548	1733	4.225	C = O stretch
1955	96.234	1955	84.724	1952	41.42	Out of phase carbonyl vibration
				2102	49.862	–C≡C– stretch
2658	84.001	2645	56.989	2649	24.86
2858	15.270	2860	18.185			C–H stretch in alkane
2952	14.386	2946	16.793	2922	4.901	C–H aromatic stretch
3516	77.050	3456	28.643	3516	7.662	OH stretch

Figure 7. Frumkin isotherm for the adsorption of NBA on mild steel and aluminium surfaces.

Table 6. Condensed Fukui indices of NBA calculated from DFT and Ab initio levels of theory.

Level of theory	Atom	$q_N$	$q_{N-1}$	$q_{N+1}$	$f_x$	$f_{x^{+}}$
Density functional theory	1 C	−0.0297	0.0862	−0.0804	−0.1159	−0.0507
	2 C	−0.0778	−0.0060	−0.0295	−0.0717	0.0482
	3 C	0.0324	0.0568	0.0394	−0.0243	0.0070
	4 C	0.0499	0.0328	−0.0697	0.0172	−0.1197
	5 C	0.0336	−0.0243	0.0309	0.0579	−0.0027
	6 C	0.0468	0.0371	0.0645	0.0097	0.0177
	7 C	0.0702	0.1263	−0.0249	−0.0561	−0.0952
	8 O	0.071	0.4135	0.0367	−0.3665	−0.0104
	9 O	−0.0192	0.1007	−0.0589	−0.1200	−0.0397
	10 N	0.0833	0.1073	0.0551	−0.0240	−0.0282
	11 O	−0.0422	0.0095	−0.1577	−0.0517	−0.1155
	12 O	−0.0383	−0.1413	−0.1481	0.1030	−0.1098
Ab initio	1 6	0.9504	1.0202	0.9228	−0.0698	−0.0276
	2 6	−0.2598	−0.2256	−0.2399	−0.0342	0.0198
	3 6	−0.1416	−0.1237	−0.1961	−0.0179	−0.0545
	4 6	0.2383	0.2813	0.2363	−0.0430	−0.0020
	5 6	−0.1727	−0.1485	−0.2251	−0.0242	−0.0524
	6 6	−0.2496	−0.2338	−0.2403	−0.0159	0.0094
	7 6	−0.1482	−0.1470	−0.2082	−0.0012	−0.0600
	8 8	−0.6205	−0.2443	−0.6586	−0.3763	−0.0381
	9 8	−0.7284	−0.5994	−0.7274	−0.1290	0.0010
	10 7	0.2680	0.1535	0.1875	0.1145	−0.0806
	11 8	−0.4014	−0.2887	−0.6202	−0.1127	−0.2187
	12 8	−0.3982	−0.2887	−0.6177	−0.1095	−0.2196

Figure 8. Micrographs of the studied metals after dipping in 0.1 M HCl solution for 7 days (a) mild steel alone (b) aluminium alone (c) mild steel + NBA (d) aluminium + NBA.

Figure 9. HOMO and LUMO diagrams of NBA molecule.