Corrosion Inhibition Performance of Lignin Extracted from Black Liquor on Mild Steel in 0.5 M H2SO4 Acidic Media

The inhibition efficiency of lignin on mild steel corrosion in 0.5 M H2SO4 increases with lignin concentration.

“Results of these studies show that lignin does inhibit the corrosion of mild steel by sulfuric acid, and that the inhibition efficiency increased with lignin's concentration.”

• Also stated in: § Weight loss measurement · boosted

  “From the results, it is clear that, as the concentration of the inhibitor increased, the surface coverage increased, leading to better inhibition efficiencies and, consequently, to lower corrosion rates.”

• Also stated in: § Conclusions · plain

  “The corrosion inhibition efficiency increases with an increased concentration of lignin, up to 1000 ppm, due to increased adsorption.”

In polarization curves for mild steel in 0.5 M H2SO4, the anodic and cathodic branches in the presence of lignin are shifted towards lower currents.

“As it can be seen from the figure and the table, the anodic and cathodic branches of the polarization curves, in the presence of lignin, are shifted towards lower currents.”

At lignin concentrations above 400 ppm, the corrosion rate of mild steel in 0.5 M H2SO4 is almost uniform at different time intervals.

“Also, at higher concentrations of lignin (above 400 ppm), the corrosion rate is almost uniform at different time intervals, indicating better and maximum surface coverages at these concentrations, even when they are exposed to lignin solutions for higher time intervals.”

Surface coverage on mild steel in 0.5 M H2SO4 increases with lignin concentration.

“From the results, it is clear that, as the concentration of the inhibitor increased, the surface coverage increased, leading to better inhibition efficiencies and, consequently, to lower corrosion rates.”

The decrease in cathodic currents is predominant compared to anodic currents in the presence of lignin.

“The extent of decrease in cathodic currents is predominant, compared to anodic currents, suggesting a higher inhibition of cathodic reactions (hydrogen or oxygen reduction), in the presence of lignin, accompanied by a weaker inhibition towards the anodic dissolution of mild steel.”

Lignin extracted from black liquor inhibits the corrosion of mild steel by 0.5 M H2SO4.

“Results of these studies show that lignin does inhibit the corrosion of mild steel by sulfuric acid, and that the inhibition efficiency increased with lignin's concentration.”

• Also stated in: § Electrochemical impedance spectroscopy (EIS) · plain

  “In Fig. 5d, pits are hardly observed, because of the inhibition action of lignin towards the corrosion of mild steel by acid.”

• Also stated in: § Conclusions · boosted

  “Based on the results of this study, it can be claimed that lignin effectively adsorbs onto the surface of mild steel, making it less prone to corrosion, even in acidic environments.”

Charge transfer resistance associated with the electrochemical reaction at the interface was much lower in the absence of inhibitor than in its presence.

“The charge transfer resistance associated with the electrochemical reaction at the interface was much lower in the absence of the inhibitor (see Table 3), indicating the ease of a corrosion reaction [13].”

In SEM micrograph after polarization of mild steel in lignin solution in 0.5 M sulfuric acid, pits are hardly observed because of inhibition action of lignin.

“In Fig. 5d, pits are hardly observed, because of the inhibition action of lignin towards the corrosion of mild steel by acid.”

After polarization, a large number of pits formed on the surface of mild steel due to corrosion by acid.

“It is very clear from the image (Fig. 5b) that, after polarization, a large number of pits was formed on the surface of the mild steel, due to its corrosion by the acid.”

Upon lignin adsorption onto mild steel in 0.5 M H2SO4, charge transfer resistance increased.

“However, when lignin was adsorbed onto the metal surface, the charge transfer resistance increased, leading to a decrease in corrosion.”

An optimum concentration of lignin is required for better corrosion inhibition of mild steel in 0.5 M H2SO4.

“Hence, it seems to be required an optimum concentration of lignin to get better corrosion inhibition results.”

EDS mapping for carbon and oxygen on mild steel surface suggests uniform adsorption of inhibitor onto substrate surface.

“EDS mapping for carbon and oxygen (main elements in lignin) given in, respectively Fig. 6a and b, on the mild steel surface, suggests uniform adsorption of the inhibitor onto the substrate's surface.”

Lignin adsorption decreases corrosion of mild steel in 0.5 M H2SO4.

“However, when lignin was adsorbed onto the metal surface, the charge transfer resistance increased, leading to a decrease in corrosion.”

The lower charge transfer resistance in the absence of inhibitor indicates ease of corrosion reaction.

“indicating the ease of a corrosion reaction [13].”

• cites [13] 13. Tsuru T, Haruyama S, Gijutsu B. J Jpn Soc Corros Eng. 1978;27:573.Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Lignin effectively adsorbs onto the surface of mild steel.

“Based on the results of this study, it can be claimed that lignin effectively adsorbs onto the surface of mild steel, making it less prone to corrosion, even in acidic environments.”

Lignin inhibits cathodic reactions (hydrogen or oxygen reduction) more than anodic dissolution of mild steel in 0.5 M H2SO4.

“The extent of decrease in cathodic currents is predominant, compared to anodic currents, suggesting a higher inhibition of cathodic reactions (hydrogen or oxygen reduction), in the presence of lignin, accompanied by a weaker inhibition towards the anodic dissolution of mild steel.”

The increase in inhibition efficiency with lignin concentration suggests a higher and better inhibitive surface modification of mild steel due to adsorption of more lignin molecules, hindering the electrochemical corrosion process.

“The inhibition efficiency increased with an increase in lignin's concentration, suggesting a higher and better inhibitive (or passive) surface modification of mild steel, due to the adsorption of more lignin molecules onto the surface, hindering the electrochemical corrosion process [14].”

• cites [14] 14. Benalli O, Larabi L, Traisnel M, et al. Appl Surf Sci. 2007;253:6130.Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Lignin contains functional groups such as -OH, -RCOOH and -ROCH3 that can adsorb onto a metal surface by sharing their lone pair of electrons with the free d-orbital of a metal.

“Thus, lignin contains various functional groups such as -OH, -RCOOH and -ROCH3 groups (Fig. 1) that can adsorb onto a metal surface by sharing their lone pair of electrons with the free d-orbital of a metal, a property that may be effectively utilized for corrosion control.”

Very high concentrations of lignin may result in increased competition between lignin molecules and adsorption sites, leading to inefficient adsorption and reduction in inhibition activity.

“However, very high concentrations of lignin may result in an increased competency between the lignin molecules and adsorption sites, leading to an inefficient adsorption, and thereby causing a reduction in inhibition activity.”

Lignin adsorption makes mild steel less prone to corrosion even in acidic environments.

“Based on the results of this study, it can be claimed that lignin effectively adsorbs onto the surface of mild steel, making it less prone to corrosion, even in acidic environments.”

Lignin is a suitable material for corrosion inhibition.

“Lignin, a phenolic polymer, is one of the suitable materials for the said purpose [13,14], as it is the second most abundant natural polymeric material, after cellulose.”

• cites [13] 13. Tsuru T, Haruyama S, Gijutsu B. J Jpn Soc Corros Eng. 1978;27:573.Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites [14] 14. Benalli O, Larabi L, Traisnel M, et al. Appl Surf Sci. 2007;253:6130.Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The shift in corrosion potentials towards more negative values in the presence of lignin suggests inhibition of cathodic reactions.

“The shift in the corrosion potentials towards more negative values, in the presence of the inhibitor, is further suggestive of the inhibition of cathodic reactions.”