Table 4 Corrosion parameters derived from polarization curves for st-37 in sulfuric acid solution with (a) inhibitor, (b) nano inhibitor, and in hydrochloric acid solution with (c) inhibitor, (d) nano inhibitor in uninhibited, and inhibited solution at 25 ± 1 °C.

C/ppm	i_corr/μA.cm⁻²	− E_corr/mV	β_c/mV.dacade⁻¹	β_a/mV.dacade^-1	θ	IE%
(a) Dracocephalum/H₂SO₄ 0.5 M
Blank	1427	413	67	59	–	–
50	327	440	61	130	0.77	77
100	249	438	55	126	0.82	82
150	222	435	53	129	0.84	84
200	151	440	51	137	0.89	89
250	199	438	53	115	0.86	86
(b) Dracocephalum (nano)/H₂SO₄ 0.5 M
25	197	439	55	143	0.86	86
50	126	447	53	136	0.91	91
75	91	454	56	135	0.94	94
100	105	443	50	135	0.93	93
(c) Dracocephalum/HCl 1.0 M
Blank	752	440	106	138	–	–
100	363	445	92	127	0.52	52
200	209	446	67	111	0.72	72
300	156	447	77	117	0.79	79
400	73	455	75	117	0.90	90
500	111	445	78	119	0.85	85
(d) Dracocephalum (nano)/HCl 1.0 M
50	217	451	71	126	0.71	71
75	168	454	71	125	0.78	78
100	87	445	62	120	0.88	88
125	182	449	68	128	0.76	76

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