Green Corrosion Inhibitors for Metal and Alloys Protection in Contact with Aqueous Saline

Abstract

Corrosion is an inevitable and persistent issue that affects various metallic infrastructures, leading to significant economic losses and safety concerns, particularly in areas near or in contact with saline solutions such as seawater. Green corrosion inhibitors are compounds derived from natural sources that are biodegradable in various environments, offering a promising alternative to their conventional counterparts. Despite their potential, green corrosion inhibitors still face several limitations and challenges when exposed to NaCl environments. This comprehensive review delves into these limitations and associated challenges, shedding light on the progress made in addressing these issues and potential future developments as tools in corrosion management. Explicitly the following aspects are covered: (1) attributes of corrosion inhibitors, (2) general corrosion mechanism, (3) mechanism of corrosion inhibition in NaCl, (4) typical electrochemical and surface characterization techniques, (5) theoretical simulations by Density Functional Theory, and (6) corrosion testing standards and general guidelines for corrosion inhibitor selection. This review is expected to advance the knowledge of green corrosion inhibitors and promote further research and applications.

Keywords: corrosion; green corrosion inhibitors; metals and alloys; saline environment.

Figure 1

Number of publications per year with the keywords “Green inhibitor corrosion protection neutral” searched in Web of Science.

Figure 2

Flow diagram scheme of database collection and methodology for the review and analysis of information on green corrosion inhibitors.

Figure 3

(a) Cathodic–anodic processes due to Cl⁻ ions without a green inhibitor, (b) passivating mechanism of anodic green inhibitor, and (c) organic compounds acting as a film through surface adsorption, forming cathodic or anodic products known as rust. Based on Kumar et al.’s results [64], where O-atoms of the Lawsonia inermis molecule form covalent bonds with Fe atoms of the metallic surface (red ball: oxygen, white ball: hydrogen, gray ball: carbon, and green ball: hydroxide).

Figure 4

Molecules structures derived from Lupine extracts. (a) lupanine, (b) multiflorine, (c) sparteine and damsissa extract (d) damsin, (e) ambrosin, (f) parthenin, (g) scopoletin, (h) umbelliferone, and (i) esculetin. Red ball: oxygen, white ball: hydrogen, gray ball: carbon, green ball: hydroxide, pink ball: CH₃, and blue ball: nitrogen.

Figure 5

Molecules structures of active compounds present in plant-based corrosion inhibitors. (a) catechin, (b) Lawsonia inermis, (c) Hibiscus rosa-sinensis Linn (Quercetin-3-O-glucoside), (d) anabasine, (e) 7-dehydrocholesterol, (f) halfabar, (g) capsaicin, (h) croweacin, (i) chitosan. Red ball: oxygen, white ball: hydrogen, gray ball: carbon, and green ball: hydroxide, pink ball: CH₃, blue ball: nitrogen.

Figure 6

Molecules structures of active compounds present in plant-based corrosion inhibitors: (a) niacin, (b) benzodiazepine, (c) Catharanthus roseus, (d) citrate, (e) curcumin. Red ball: oxygen, white ball: hydrogen, gray ball: carbon, and green ball: hydroxide, pink ball: CH₃, blue ball: nitrogen.

Figure 7

Potentiodynamic polarizations for mild steel in 3.5% NaCl solution in the absence and presence of various concentrations of hexane extract of Vicia faba at 298 K [174].

Figure 8

Electrochemical results for carbon steel in 0.5 M NaCl + 600 ppm DR (N₂) at different immersion times: (a) polarization curves; (b) Nyquist diagram; (c) Bode magnitude diagram; and (d) Bode phase angle diagram. Marks and continuous lines in EIS diagrams indicate the experimental and fitted data, respectively [166].

Figure 9

SEM/EDS micrographs of iron after immersion for 24 h in 3% NaCl solution without (Blank) and with 100 ppm ethanol extract of Lentisk leaf (EELL) [177].

Figure 10

FTIR results of Aerva lanata [93].

Figure 11

C 1s, O 1s, N 1s, and Zn 2p XPS deconvoluted profiles for zinc surface treated with Bagassa guianensis plant extract in 3% NaCl at 25 °C [92].

Figure 12

AFM 2D and 3D micrographs for α-brass electrode after 24 h immersion in 3.5% NaCl polluted by 16 ppm of sulfur ions (A) without and (B) with 300 ppm myrrh extract [123].

Figure 13

Two-dimensional and three-dimensional atomic force micrographs of 316L stainless steel: (a,a′) before immersion (polished), (b,b′) after immersion in 3% NaCl, and (c,c′) after immersion in 3% NaCl + 1600 ppm Thymus satureoides during 24 h, (d) calculated roughness (z-z*) factor for 316L stainless steel: (a) before immersion (polished), (b) after immersion in 3% NaCl, and (c) after immersion in 3% NaCl + 1600 ppm Thymus satureoides inhibitor during 24 h [181].

Figure 14

SEM image of 316L stainless steel: (a) before immersion (polished), (b) after immersion in 3% NaCl, and (c) after immersion in 3% NaCl + 1600 ppm inhibitor during 24 h [181].

Figure 15

(a) HOMO and LUMO surfaces of neutral main alkaloids of C. roseus and (b) scheme of C. roseus extracts adsorbed on 111 mild steel surface [79].

Figure 16

Advantages of using plant extracts as corrosion inhibitors.