Effectiveness of Irvingia wombolu extract on corrosion inhibition of mild steel in hydrochloric acid solution (2025)

Author e-mails

kc.nnakwo@unizik.edu.ng

Author affiliations

¹ Department of Metallurgical and Materials Engineering, Enugu State University of Science and Technology, Agbani, Nigeria

² Department of Metallurgical and Materials Engineering, Nnamdi Azikiwe University, Awka, Nigeria

ORCID iDs

Kingsley Chidi Nnakwo https://orcid.org/0000-0001-7322-9349

Dates

1. Received 30 December 2019
2. Revised 20 February 2020
3. Accepted 21 February 2020
4. Published 2 March 2020

Peer review information

Method:Double-anonymous
Revisions:2
Screened for originality? Yes

Nwazico laboratory Onitsha, Anambra State, Nigeria, supplied the materials used for this experiment. The materials include mild steel, absolute ethanol, 1.5M hydrochloric acid, and distilled water. About 22 coupons of dimensions 2 cm × 2 cm × 1 cm were prepared from a mild steel sample. The mild steel is of composition Fe-99.07, C- 0.15, S-0.03, Si-0.02, Mn-0.71, Cr-0.01, and P-0.02 (in wt%) as obtained from the chemical analysis using x-ray fluorescence. The mild steel underwent surface preparation (grinding and polishing) using a rotating electric grinder and silicon carbide paper of 400 μm, 800 μm, and 1200 μm grit sizes. The ground mild steel coupons were subjected to intense polishing using aluminium oxide powder, degreased with absolute ethanol for 1 h, and dried using Bosch PHG500-2-1600W hot air gun machine.

The fresh Irvingia wombolu leaves obtained from Obolo Afor, Enugu State, Nigeria, as presented in figure 1, underwent thorough washing with distilled water, dried with Bosch PHG500-2-1600W hot air gun machine, and ground using an SB-1872 electric blender. The ground leaves were soaked in 500 ml absolute ethanol for 24 h and filtered using a Whatman paper. The filtrate underwent drying at 70 °C for 6 h, using a KW-1000DC thermostat water bath, and the required extract concentrations (0.2 g, 0.5 g, and 1 g) measured using a BL20001 electronic compact scale.

This present study adopted the weight loss technique in assessing the corrosion level of mild steel in 1.5M hydrochloric acid solution. Firstly, the dimensions and weight of each specimen were determined and recorded. The prepared mild steel specimens were placed inside beakers containing a solution of 1.5M HCl with and without extracts additions. The beakers were placed inside a digital water bath maintained at required temperatures (299 K and 303 K) for 2, 4, 6, 8, 10, and 12 h respectively. On attaining the required time, the beakers were removed from the water bath and the specimens removed from the solution. The specimens were cleaned, dried and the corrosion products in each specimen were scrapped off and kept secured in an air tight container for the FTIR analysis. The corrosion rate and the level of inhibition were determined using equations (1) and (2) respectively (Onah et al 2019).

where Cr_o equals the corrosion rate (in mm yr⁻¹), W_b-W_a equals different in weight of specimen before and after immersion (in gram), z equals area of the specimen (in mm²), t equals the time of exposure (in h) and ρ equals specimen density (in g mm⁻³).

where ε equals the inhibition efficiency, Cr_o equals the corrosion rate with no extracts addition, Cr_i equals the corrosion rate with extracts addition.

The interaction of the extract with the mild steel molecules was determined using equations (3) and (4) (Onah et al 2019). This was done taking into consideration the calculated percentage inhibition efficiency and the extract dispersion on the specimens' surface also known as the surface coverage (θ). Using equation (3), θ was calculated and the interrelationship between the degree of θ and extract concentration was also calculated using equation (4).

where c is the extract concentration and K_ads is the adsorption coefficient.

Table 1 shows the effect of varying concentrations of Irvingia wombolu extract on the corrosion rate of mild steel in 1.5M HCl solution at various immersion times (2–12 h) and solution temperatures (299 K and 303 K). The inhibition efficiency of the extract on mild steel corrosion in 1.5M HCl solution is also revealed in table 1. Table 1 revealed the corrosion rate as a function of time (2–12 h) and temperature, as it increased correspondingly with increasing immersion time and solution temperature. Without extract addition, the corrosion rate increased from 10.884 mm yr⁻¹ to 11.481 mm yr⁻¹ as the solution temperature increased from 299 K to 303 K for 2 h respectively. Increasing the immersion time from 2 h to 12 h at solution temperatures of 299 K and 303 K, the corrosion rate increased from 10.884 mm yr⁻¹ to 18.481 mm yr⁻¹ and from 11.481 mm yr⁻¹ to 21.162 mm yr⁻¹ respectively. At 299 K and 303 K, addition of 0.2 g l⁻¹ Irvingia wombolu extract drastically reduced the corrosion rate from 10.884 mm yr⁻¹ to 3.833 mm yr⁻¹ and from 11.481 mm yr⁻¹ to 4.420 mm yr⁻¹ respectively at immersion time of 2 h. The inhibition efficiencies of the Irvingia wombolu extract (0.2 g l⁻¹) at solution temperatures of 299 K and 303 K for 2 h immersion time are 64.8% and 61.5% respectively, indicating about 5.1% decrease in inhibition performance. Increasing the concentration of Irvingia wombolu extract from 0.2 g l⁻¹ to 1 g l⁻¹ caused a further reduction of the corrosion rate with maximum inhibition efficiency obtained at 12 h immersion time. At 299 K, 1 g l⁻¹ extract reduced the corrosion rate to 2.402 mm yr⁻¹ (77.93% inhibition), but recorded a corrosion rate of 3.224 mm yr⁻¹ (71.92% inhibition) at 303 K, for 2 h immersion time respectively. The corrosion rate decreased to 0.394 mm yr⁻¹ (97.87% inhibition) and 0.490 mm yr⁻¹ (97.68% inhibition) after 12 h immersion time at 299 K and 303 K respectively. Umoren et al (2016) in their study attributed the inhibitive performance of plant extract to adsorption of extract molecules on mild steel surface. Hence, the drastic reduction of the corrosion rate by the Irvingia wombolu extract addition could also be linked to the adsorbed extract functional group (O–H, H–C=O, C–O, –C≡C–H, C–Cl, =C–H, C–F, C–C, N–H, C–H, and –C≡C–) as evidence in the FTIR result.

Minimum corrosion rates, indicating maximum inhibition efficiencies are obtained with higher extract concentration, longer immersion time (12 h), and lower solution temperature (299 K). Table 2 shows the extract dispersion on the surface of mild steel samples (surface coverage (θ)) and the interrelationship between the degree of θ and the extract concentration. Figures 2 and 3 show the LAI plots for Irvingia wombolu extract at different temperatures of immersion (299 K and 303 K) for 12 h. The plots show linear trends with 1.0092 and 0.998 as slopes at 299 K and 303 K respectively. The adsorption of molecules of Irvingia wombolu on the mild steel surface obeys the Langmuir adsorption isotherm.

Table 3 and figures 4 and 5 show the FTIR results of the Irvingia wombolu extract and the corrosion product scrapped from the surfaces of mild steel samples immersed in 1.5M HCl solution containing different concentrations of Irvingia wombolu extract. Figures 4 and 5 showed that the FTIR spectra of the extract and the corrosion product from the mild steel immersed in 1.5M HCl containing different concentrations of Irvingia wombolu extract are similar. Table 3 showed that all the functional groups in the Irvingia wombolu extract are also found in the corrosion product of the inhibited mild steel, but with different wavelength. For example, the C–O stretching at 1246.87 cm⁻¹ shifted to 1252.565 cm⁻¹, N–H stretching at 1499.76 cm⁻¹ shifted to 1603.372 cm⁻¹, –C≡C– stretching at 2044.312 cm⁻¹ shifted to 2154.015 cm⁻¹, and the –C≡C–H stretching at 3261.221 cm⁻¹ shifted to 3309.113 cm⁻¹ on the corrosion product. The hydroxyl (OH) functional group was shifted from 3359.433 cm⁻¹ to 3445.372 cm⁻¹. These shifts in the wavelength of the functional groups in the corrosion product indicate the interaction between molecules of Irvingia wombolu extract and the mild steel surface. This agrees with the findings of Umoren et al (2016).

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