Some natural aqueous extracts of plants as green inhibitor for carbon steel corrosion in 0.5 M sulfuric acid

Figures & data

Table 1. The IUPAC name, molecular weight and molecular formula of the major component found in the three natural extracts used as green corrosion inhibitors.

Natural compound	IUPAC name	Molecular weight (g/mol)	Molecular formula
Curcumin extract	(1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6- diene-3,5-dione	368.385	C21H20O6
Parsley extract	chromen-2-one;3,7-dimethylocta-1,6-dien-3-ol;17-(5-ethyl-6-methylheptan-2-yl)-10,13-dimethyl-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol	715.116	C48H74O4
Cassia bark extract	[3,5-dihydroxy-4,6-bis[(3,4,5-trihydroxybenzoyl)oxy]oxan-2-yl]methyl3,4,5-trihydroxybenzoate;(Z)-3-phenylprop-2-enal	768.627	C36H32O19

Figure 1. Effect of various concentrations of cassia bark extract on the galvanostatic polarization curves for C-steel in 0.5 M H₂SO₄. (1) 0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5) 400 ppm and (6) 500 ppm.

Table 2. Corrosion parameters obtained from galvanostatic polarization measurements of C-steel in 0.5 M H₂SO₄ solution containing different concentrations of natural extracts of curcumin, parsley and cassia bark.

Comp.	Cons, ppm	ba, mV dec^−1	bC, mV dec^−1	Ecorr, mV (SCE)	icorr, mA cm^−2	%IE
0.5 M H2SO4	0.5 M H2SO4	69.5	91	478	0.712	–
Curcumin extract	100	153	152	522	0.389	45.36
	200	156	170	541	0.340	52.25
	300	173	180	544	0.242	66.01
	400	180	188	543	0.165	76.82
	500	193	200	551	0.135	81.04
Parsley extract	100	143	141	533	0.372	47.75
	200	164	176	537	0.295	58.56
	300	168	181	541	0.212	70.22
	400	177	188	543	0.144	79.77
	500	190	196	548	0.116	83.70
Cassia bark extract	100	141	165	511	0.366	48.59
	200	148	157	522	0.298	58.14
	300	157	178	537	0.186	72.51
	400	165	183	538	0.142	80.05
	500	175	193	541	0.095	86.66

Figure 2. Potentiodynamic anodic polarization curves of C-steel in 0.5 M H₂SO₄ containing different concentrations of cassia bark extract at a scan rate of 50 mV/s. (1) 0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5) 400 ppm and (6) 500 ppm.

Table 3. Corrosion parameters obtained from potentiodynamic anodic polarization measurements of C-steel in 0.5 M H₂SO₄ containing different concentrations of natural extracts of curcumin, parsley and cassia bark at a scan rate 50 mV/s.

Comp.	Conc, ppm	ip, mA cm^−2	Ep, V (SCE)	%IE
0.5 M H2SO4	0.5 M H2SO4	4.99	0.76	–
Curcumin extract	100	2.74	0.74	45.09
	200	2.46	0.69	50.70
	300	1.62	0.65	67.53
	400	1.13	0.60	77.35
	500	0.88	0.54	82.36
Parsley extract	100	2.69	0.72	46.09
	200	2.35	0.74	52.90
	300	1.54	0.68	69.14
	400	1.08	0.62	78.35
	500	0.77	0.56	84.57
Cassia bark extract	100	2.65	0.66	46.89
	200	2.30	0.63	53.91
	300	1.49	0.49	70.14
	400	1.01	0.38	79.75
	500	0.62	0.35	87.57

Figure 3. Potentiodynamic anodic polarization curves of carbon steel in 0.5 M H₂SO₄ + 0.5 M NaCl solutions containing different concentrations of cassia bark extract at a scan rate1 mV/s. (1) 0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5) 400 ppm and (6) 500 ppm.

Figure 4. The relation between the pitting potential of C-steel and logarithm the concentration of natural extracts. (1) Curcumin extract, (2) parsley extract and (3) cassia bark extract.

Figure 5. Weight loss as a function of time of C-steel in 0.5 M H₂SO₄ solution without and with cassia bark extract: (1) 0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5) 400 ppm and (6) 500 ppm.

Table 4. Variation of degree of surface coverage (θ), corrosion rate (k) and percentage inhibition efficiency (%IE) of C-steel in the presence of different concentrations of curcumin, parsley and cassia bark extracts.

Comp.	Conc, ppm	K, mg cm^−2 min^−1	θ	%IE
0.5 M H2SO4	0.5 M H2SO4	7.35	–	–
Curcumin extract	100	4.12	0.439	43.94
	200	3.45	0.531	53.06
	300	2.46	0.665	66.53
	400	1.75	0.762	76.19
	500	1.27	0.827	82.72
Parsley extract	100	3.85	0.476	47.62
	200	3.38	0.540	54.01
	300	2.25	0.694	69.38
	400	1.58	0.785	78.50
	500	1.12	0.848	84.76
Cassia bark extract	100	3.73	0.492	49.25
	200	3.12	0.575	57.55
	300	2.08	0.717	71.70
	400	1.42	0.807	80.68
	500	0.88	0.880	88.02

Figure 6. Curve fitting of the corrosion data for C-steel in 0.5 M H₂SO₄ solution in presence of different concentrations of natural extracts to the Temkin’s adsorption isotherm. (1) Curcumin extract, (2) parsley extract and (3) cassia bark extract.