Paprika extract: a green inhibitor for mitigating carbon steel disintegration in 1 M HCl pickling solution

Figures & data

Figure 1. Chemical structure of the Capsaicin compound.

Table 1. Variation of the corrosion rate, and inhibition efficiency, with the concentration of the Paprika extract at different temperatures.

Temperature ( K)	Concentration (ppm)	Weight Lack (mg/cm^2)	CR (mg/cm^2/min)	IE (%)
298	Blank	0.88	7×10^−3	---
	50	0.68	6×10^−3	22.7 ±0.6
	100	0.48	4×10^−3	45. 5 ±0.4
	150	0.45	4×10^−3	48.9 ±0.3
	200	0.42	4×10^−3	52.2 ±0.5
	250	0.38	3×10^−3	56.8 ±0.8
	300	0.34	3×10^−3	61.4 ±0.2
303	Blank	1.49	12×10^−3	---
	50	0.66	6×10^−3	55.7 ±0.3
	100	0.56	5×10^−3	62.4 ±0.8
	150	0.51	4×10^−3	65.8 ±0.6
	200	0.50	4×10^−3	66.4 ±0.5
	250	0.43	4×10^−3	71.1 ±0.4
	300	0.36	3×10^−3	75.8 ±0.2
308	Blank	6.75	56×10^−3	---
	50	0.91	8×10^−3	86.5 ±0.8
	100	0.73	6×10^−3	89.2 ±0.9
	150	0.62	5×10^−3	90.8 ±0.7
	200	0.56	5×10^−3	91.7 ±0.5
	250	0.46	4×10^−3	93.2 ±0.5
	300	0.11	4×10^−3	93.7 ±0.3
313	Blank	7.79	65×10^−3	---
	50	1.03	9×10^−3	86.8 ±0.2
	100	0.75	7×10^−3	90.7 ±0.4
	150	0.6	6×10^−3	92.3 ±0.7
	200	0.54	6×10^−3	93.1 ±0.9
	250	0.42	5×10^−3	94.6 ±02
	300	0.39	5×10^−3	95± 0.4

Figure 2. Langmuir adsorption isotherms for the Paprika extract on carbon steel different temperatures.

Figure 3. Frumkin adsorption isotherms for the Paprika extract on carbon steel different temperatures.

Figure 4. Freundlich adsorption isotherms for the Paprika extract on carbon steel different temperatures.

Figure 5. Temkin adsorption isotherms for the Paprika extract on carbon steel different temperatures.

Table 2. Adsorption parameters of the Paprika extract on carbon steel in 1M HCl at different temperatures.

Temperature (K)	K ads (M^−1)	-ΔG° (kJmol^−1)	- ΔH° (kJmol^−1)	ΔS° (J mol^−1 K^−1)
298	6.3	14.5	22	−25.1
303	12.9	16.6		−17.7
308	24.6	18.5		−11.4
313	211.9	24.4		7.6

Figure 6. Potentiodynamic Polarization curves for carbon steel in 1 M HCl without and with various concentrations of the Paprika extract at 298 K.

Table 3. Potentiodynamic polarization parameters of carbon steel in 1M HCl without and with various concentrations of the investigated extract at 25°C.

Concentration (ppm)	I × 10^–6 (A / cm^2)	Ecorr × 10^–3 (V)	βa × 10^–3 (V/decade)	-βc × 10^–3 (V/decade)	θ	IE(%)
Blank	404	−527	89.9	121.7	-	-
50	231	−451	139.9	126.9	0.43	43 ±0.5
100	215	−425	102.2	115.9	0.47	47 ±0.3
150	191	−495	149.8	129.0	0.53	53 ±0.8
200	177	−448	167.4	145.4	0.56	56 ±0.7
250	163	−450	131.1	126.7	0.60	60 ±0.2
300	157	−448	178.4	92.7	0.61	61 ±0.5

Figure 7. The Nyquist (a) and Bode-phase angle (b) plots of carbon steel in 1 M HCl in the absence and presence of various concentrations of the Paprika extract at 298 K.

Figure 8. Electrical equivalent circuit used to model the results of impedance.

Table 4. EIS parameters for carbon steel corrosion in the absence and presence of various concentrations of the Paprika extract at 25°C.

Concentration (ppm)	Rct (Ω cm^2)	Cdl × 10^–6 (F cm^−2)	θ	IE (%)
Blank	40.7	67.0	-	-
50	62.5	42.5	0.35	35 ±0.5
100	68.5	25.1	0.40	40 ±0.8
150	86.2	23.4	0.53	53 ±0.5
200	122.6	20.2	0.67	67 ±0.7
250	147.9	15.2	0.73	73 ±0.2
300	160.8	13.5	0.75	75 ±0.6

Figure 9. EFM data for carbon steel in 1 M HCl in the absence and presence of different concentrations of the Paprika extract at 298 K.

Table 5. EFM parameters for carbon steel in 1 M HCl in the absence and presence of different concentrations of the Paprika extract.

Concentration(ppm)	I × 10^−6(A/ cm^2)	βa(V/decade)	-βc(V/decade)	CF-2	CF-3	θ	IE(%)
Blank	628	98	126	2.70	2.90	-	-
50	296	97.7	104.2	2.35	2.84	0.53	53 ±0.2
100	279	101.8	122.5	2.72	2.57	0.56	56 ±0.6
150	247	134.1	156.4	2.58	2.80	0.61	61 ±0.7
200	190	130.7	143.8	2.34	2.98	0.70	70 ±0.2
250	172	133.6	142.7	2.50	3.64	0.73	73 ±0.3
300	160	106.4	130.5	2.08	3.56	0.75	75 ±0.9

Figure 10. ATR-IR spectra of the Paprika extract and Paprika extract in the presence of 1M HCl, and carbon steel.

Figure 11. SEM images of carbon steel in 1 M HCl (a) and in 1M HCl + 300 ppm Paprika extract.

Table 6. Comparison between the tested Paprika extract and other plant extracts reported in the literature.

Name of the extract	I Inhibition efficiency	Reference
Rosa canina	86 % at 800 ppm	[62]
Tinospora crispa	80 % at 1000 ppm	[63]
Glycyrrhiza glabra	88% at 600 ppm	[64]
Euphorbia heterophyllallinneo	69% at 1000 ppm	[65]
Eucalyptus	88 % at 800 ppm	[66]
Dioscorea septemloba	72% at 200 ppm	[67]
Cyptocarya nigra	91% at1000 ppm	[68]
Ziziphora	93 % at 800 ppm	[69]
Pterocarpus santalinoides	90 5 at 700 ppm	[70]
Paprika	95% at 300 ppm	This work

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