Electrochemical and Economic Evaluation of the Cocoa Bean Shell as a Corrosion Inhibitor in Acidic Medium

Carvalho, Mayara Cristina Fernandes de; Almeida, Nayara Maria Santos de; Silva, Iago Magella Fernandes Costa Rossi e; Cotting, Fernando; Aoki, Idalina Vieira; Capelossi, Vera Rosa

doi:10.1590/1980-5373-MR-2021-0125

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Article • Mat. Res. 25 • 2022 • https://doi.org/10.1590/1980-5373-MR-2021-0125 copy

Electrochemical and Economic Evaluation of the Cocoa Bean Shell as a Corrosion Inhibitor in Acidic Medium

Authorship SCIMAGO INSTITUTIONS RANKINGS

The inhibition effect of the cocoa bean shell powder (CBSP) on SAE 1008 carbon steel was studied in acidic medium (HCl 0.5 mol L^-1) by electrochemical techniques and gravimetric measurements. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to the chemical and morphological characterization. The gravimetric and EIS results showed that the corrosion rate decreases with increasing inhibitor concentration, reaching the maximum value of 97.92% in 1.77 g L^-1 inhibitor (highest concentration studied). Even at the lowest concentration (0.44 g L^-1) good corrosion inhibition efficiency (96.03%) was observed. The polarization curves indicated that the CBSP acts as a mixed type inhibitor. The inhibitory molecules adsorption followed the Langmuir isotherm model. The inhibitor economic evaluation showed that the use of CBSP is 48-616 times cheaper than traditional inhibitors. The results showed that CBSP is an efficient corrosion inhibitor for carbon steel and its production is financially attractive.

Keywords:
Carbon Steel; Cocoa bean shell; Natural Corrosion Inhibitor; EIS; SVET

Compound	*Concentration (g L^-1)*	Efficiency (%)
Pyrazolone	0.90	78.0
Benzethonium chloride	0.16	92.3
Benzotriazole	0.30	90.0
Benzothiazole	0.40	94.0
Dibenzylthiourea	0.05	90.0

Compound	*Average price (USD kg^-1)*
Pyrazolone	150 ± 34
Benzethonium chloride	333 ± 44
Benzotriazole	195 ± 46
Benzothiazole	192 ± 44
Dibenzylthiourea	1930 ± 150

Bands Wavenumber (cm^-1)	Functional Group attribution
3600 – 3200	O-H
3500 – 3100	N-H
3000 – 2850	C-H alkanes (stretching)
2900 – 2800	C-H (aldehyde)

*Inhibitor Concentration (g L^-1)*	*R_s (Ω cm²)*	*R_ct (Ω cm²)*	CPE_dl (F cm^-2s^(α-1))	α	χ ²	Inhibition Efficiency (%)
Blank	6.09	11.6	4.79x10^-4	0.88	1.25x10^-4	-
0.44	6.36	293.0	5.72x10^-5	0.87	1.76x10^-4	96.03
0.77	5.95	356.9	5.22x10^-5	0.87	3.01x10^-4	96.74
1.11	6.14	454.4	5.44x10^-5	0.87	1.84x10^-4	97.44
1.44	6.14	485.6	5.06x10^-5	0.87	1.65x10^-4	97.60
1.77	6.20	559.4	5.04x10^-5	0.87	2.42x10^-4	97.92

*Inhibitor concentration (g L^-1)*	E_corr (mV)	*I_corr (µA cm^-2)*	*b_a (mV dec^-1)*	*- b_c (mV dec^-1)*	IE _Icorr ( %)
Blank	- 389	1989	166	258	-
0.44	- 374	103	75	138	94.83
0.77	- 376	61	73	127	96.92
1.11	- 380	52	75	129	97.39
1.44	- 387	39	74	122	98.03
1.77	- 383	35	72	118	98.22

*Inhibitor concentration (g L^-1)*	*C_R (g cm^-2 h^-1)*	*i_corr (A cm^-2)*	Θ	η (%)
Blank	2.24x10^-3	2.15x10^-3	-	-
0.44	1.55x10^-4	1.49x10^-4	0.930	93.05
0.77	1.14x10^-4	1.10x10^-4	0.949	94.92
1.11	1.05x10^-4	1.01x10^-4	0.953	95.31
1.44	6.73x10^-5	6.46x10^-5	0.969	96.99
1.77	5.95x10^-5	5.71x10^-5	0.973	97.34

Adsorption Isotherms	R²	Equations of a straight line
Langmuir (C/θ versus C)	0.9999	y = 0.0329 + 1.0104x
Freundlich (log θ versus log C)	0.9637	y = – 0.0198 + 0.0324x
Temkin (θ versus log C)	0.9626	y = 0.9555 + 0.0710x
Frumkin (log (θ/(1–θ)/C) versus θ)	0.4760	y = 4.5104 – 3.2989x
El-Awady (log(θ/1– θ)) versus log C)	0.7981	y = 1.0064x + 1.4112

Item	*Cost (USD kg^-1)*
Transport	1.94
Drying process	0.72
Grinding process	0.02
Sieving process	0.01
Total	2.69

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