Aqueous Extracts of the Castor Beans as a Corrosion Inhibitor of Mild Steel in HCl Media

Abstract

The present work studied aqueous extracts of castor beans as a natural inhibitor of the corrosion of mild steel in 1 M HCl using gravimetric tests, potentiodynamic polarization curves, linear polarization method, electrochemical impedance measurements, surface analysis by scanning electron microscopy (SEM) and chemical characterization by Fourier transform infrared spectroscopy (FTIR). Gravimetric tests showed that inhibition efficiency (IE) increased with immersion time and concentration of the extract, reaching 97.8% in the presence of 800 mg L −1 inhibitor after 24 h immersion time. For the gravimetric tests varying the temperature, a decrease of the activation energy (E a) was observed, suggesting chemical adsorption of extract components on the metal surface. The extracts from the castor beans acted as a good corrosion inhibitor, and the macromolecules present in the high molecular weight fraction (HMWF) have a fundamental participation in this process since it presented 93.7% of IE for 200 mg L −1 .

Application of an Aqueous Extract of Cotton Seed as a Corrosion Inhibitor for Mild Steel in HCl Media

“…It is also stated that extremely low concentrations of ACSE provided a high IE result as 88.5% for 10 mg L −1 , and that the presence of 400 mg L −1 of the HMWF showed a similar loop seen for 800 mg L −1 of ACSE; resulting in the same IE (97.3%). These results suggest once again that the macromolecules can be the main responsible for the inhibitory effect 10,11,16,23,24,26 . The diagrams of Bode ( Figure 5) show a single time constant for all curves with a little frequency shift towards lower frequencies in the presence of the inhibitor, where the maximum phase angle for the blank assay is close to 39° and this value increases significantly in the presence of 10 mg L −1 of CSE (~ 61°), however above 50 mg L −1 the phase angle keeps quite constant, achieving a value close to 65° at 800 mg L −1 .…”

“…The presence of ACSE and its HMWF displaced the OCP to more positive values with a maximum displacement of +24 mV while the E corr shifted to more negative values, with a maximum displacement of −26 mV in the presence of 400 mg L −1 ACSE, demonstrating that the extract acts as a mixed-type inhibitor with a cathodic character when polarized. The anodic Tafel constant did not significantly change with the extracts addition, suggesting that both ACSE and its HMWF do not change the mechanism of the anodic reaction 11,23,29 . However, the cathodic Tafel constant increased (in module) from the addition of 50 mg L −1 of ACSE and its HMWF which can be explained by a change of the cathodic reaction mechanism.…”

“…We have studied the inhibitory action of some aqueous oilseed extracts like castor beans and soybean meal extracts towards the mild steel corrosion in acidic media. 800 mg L −1 aqueous castor beans and soybean meal extracts showed inhibition efficiency of 94.4 and 88.8%, respectively, from weight loss data after 2 h immersion 23,24 . The idea would be the use of the cotton cake, a residue obtained from the oil and biodiesel cotton production, as a new corrosion inhibitor.…”

“…In this sense, oil-bearing seeds could be an excellent source of compounds with anti-corrosion properties. Brazil has a diversity of oilseeds such as cotton, castor beans, soybean and oil palm, a variety of plants and natural products 23,24 . Cotton seeds (Gossypium hirsitum L.) contain carbohydrates (45.06% w/w), lipids (21.29% w/w), proteins (23.28% w/w), water (6.92% w/w) and mineral residue known as ashes (3.44% w/w) 25 .…”

“…As cotton seed presents high protein content, it may perform an important role in inhibiting steel acidic corrosion. In our previous works it was showed that the macromolecules as proteins and/or polyssacharides can be important in the inhibitive action towards the mild steel corrosion in acidic medium 11,16,[21][22][23][24]26 . We have studied the inhibitory action of some aqueous oilseed extracts like castor beans and soybean meal extracts towards the mild steel corrosion in acidic media.…”