The strict environmental legislations and increasing ecological awareness among scientists have led to the development of “green” alternatives to mitigate corrosion. In the present work, literature on green corrosion inhibitors has been reviewed, and the salient features of our work on green corrosion inhibitors have been highlighted. Among the studied leaves, extract
Among the several methods of corrosion control and prevention, the use of corrosion inhibitors is very popular. Corrosion inhibitors are substances which when added in small concentrations to corrosive media decrease or prevent the reaction of the metal with the media. Inhibitors are added to many systems, namely, cooling systems, refinery units, chemicals, oil and gas production units, boiler, and so forth. Most of the effective inhibitors are used to contain heteroatom such as O, N, and S and multiple bonds in their molecules through which they are adsorbed on the metal surface. It has been observed that adsorption depends mainly on certain physicochemical properties of the inhibitor group, such as functional groups, electron density at the donor atom,
Plant extracts investigated as corrosion inhibitors by other authors.
S. no. | Inhibitors used | Active constituents | Inhibition efficiency (%) | Remarks |
(1) | 95.0 | The aqueous extract of the leaves of henna (lawsonia) as the corrosion inhibitor was reported in C steel, nickel and zinc in acidic, neutral and alkaline solutions, using the polarization technique [ | ||
(2) | 92.2 | The temperature effects were investigated on mild steel corrosion in 2.0 M of HCl and H2SO4 in the absence and presence of aqueous extract of fenugreek leaves (AEFLs) with the help of gravimetric method [ | ||
(3) | 93.0 | The inhibitive action of the aqueous extract of olive leaves was reported towards the corrosion of C-steel in 2 M HCl solution using weight loss measurements, Tafel polarization, and cyclic voltammetry [ | ||
(4) | Anagyrine, cytisine | 67.0 | Plant extracts were investigated on the corrosion of X52 mild steel in aqueous 20% (2.3 M) sulphuric acid. Weight loss determinations and electrochemical measurements were also performed [ | |
(5) | 99.6 | The inhibition effect of | ||
(6) | Reserpine, ajmalicine, ajmaline, isoajmaline, ajmalinine, chandrine | 94.0 | ||
(7) | 86.5 | The behaviour of the inhibitive effect of lupine ( | ||
(8) | 91.3 | The acid extracts of | ||
(9) | Monoterpene, triterpene indole alkaloid, saponins | 76.0 | The inhibitive action of ethanol extracts from leaves (LV), bark (BK), and roots (RT) of | |
(10) | 97.4 | The efficacy of an acid extracts of leaves of | ||
(11) | 99.3 | The inhibitive effect of the extract of Khillah ( | ||
(12) | Emblicanin A&B, puniglucanin, pedunculagin, tannic acid, chebulinic acid, and gallic acid | 80% | Extracts were used in 5% (w/v) commercial hydrochloric acid as corrosion inhibitors of mild steel exposed into 5% (w/v) hydrochloric acid at 328 K on mild steel. Both Tafel polarization and linear polarization resistance techniques were used. Remarkable decrease in corrosion current and increase in linear polarization resistance values were observed in the presence of the acid extracts [ | |
(13) | Papain, carpaine, chymopapain, azadirachtin, salannin, gedunin, and azadirone | 87% | Extracts were used as corrosion inhibitors for corrosion of mild steel. The percentage inhibition of efficiency was found to increase with the increase in concentration of both inhibitors [ | |
(14) | Pulegone | 80% | Natural oil extracted from pennyroyal mint ( | |
(15) | Terpineol, isoxazolidine, and imidazolinedione | 85% | The inhibition effect of | |
(16) | Thyme | Thymol, malic acid, salicin, glutamic acid, leucine, and methionine | 85% | Electrochemical impedance spectroscopy has been successfully used to evaluate the performance of these compounds. The ac measurements showed that the dissolution process is activation controlled. Potentiodynamic polarization curves indicate that the studied compounds are mixed-type inhibitors. Thyme, which contained the powerful antiseptic thymol as the active ingredient, offers excellent protection for steel surface [ |
(17) | Lawsone, esculetin, fraxetin, allantoin, sterols, and hordenine | 90% | Extracts were used as corrosion inhibitors for steel, aluminum, copper, and brass in acid chloride and sodium hydroxide solutions using weight loss, solution analysis, and potential measurements. Only, | |
(18) | Scopolamine, b-sitosterol, daturadiol, tropine, and daturilin | 86% | Acid extract of the | |
(19) | Ricinoleic or ricinic acid, ricinolein, and palmitin | 84% | The corrosion behaviour of plant extract ( | |
(20) | Pugelone, alpha-pinene, limonene, methone, and piperitone | 80% | ||
(21) | Chymopapain, pectin, carposide, carpaine, pseudocarpaine, dehydrocarpines, carotenoids, cryptoglavine, | 92% | Acid extracts of the different parts of | |
(22) | Catechu, dimethyltryptamine (DMT) | 95% | The inhibitive effect of the gum exudate from | |
(23) | a-and b-Amyrins, cyanidin-3-rhamnoglucoside, cycloart-23-en-3b, 25-diol, cyclosadol | 89% | Extract of the | |
(24) | Centellin, asiaticin, and centellicin | 86% | ||
(25) | Allyl cysteine sulfoxide, methyl allyl thiosulfinate, allicin, diallyl disulfide, diallyl trisulfide, ajoene, pogostone, friedelin, epifriedelinol, pachypodol, retusine, and oleanolic acid | 94% | Plant extracts on the corrosion of steel in aqueous solution of I N sulphuric acid were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques [ | |
(26) | Tannic acid | 83% | Mature leaves of | |
(27) | Alkaloids, flavonoids, geraniin, hypophyllanthin, and phyllanthin | The inhibitive action of leaves (LV), seeds (SD), and a combination of leaves and seeds (LVSD) extracts of | ||
(28) | azadirachtin, azadirone, gedunin, nimbin, nimbandiol, nimbinene, nimbolide, nimonol, nimbolin, salannin,margolone, melianol, vilasanin, and flavanoids | 80% | The inhibitive action of leaves (LV), root (RT), and seeds (SD) extracts of | |
(29) | Gallocatechin and dopamine | 71% | The inhibition of the corrosion of mild steel by ethanol extract of | |
(30) | 80% | The inhibitive action of extract of curry leaves ( | ||
(31) | biotin, cytidine, inosine, guanine, guanosine, and riboflavin | 90% | The inhibitive effect of water and alcoholic extracts of | |
(32) | Liriodenine, azafluorenones alkaloids | 86% | The inhibition effect of alkaloids extract from | |
(33) | Vasicine, vasicinone, asiaticoside, wedelolactone, | 99% | The inhibitive action of the extracts of | |
(34) | 99% | A comparative study of the inhibitory effect of plant extracts, | ||
(35) | Liriodenine and oxoanalobine | 84% | Alkaloids extract from | |
(36) | The paper provides information on the use of ethanol extract of | |||
(37) | The inhibition of low-carbon-steel corrosion in 1 M HCl and 0.5 M H2SO4 by extracts of | |||
(38) | 87% | Corrosion inhibition efficiency of acid extract of dry | ||
(39) | 3-epikatonic acid 7-o-beta-(2-rhamnosyl-glucosyl) myricetin, ash, astragalin, caffeic acid, and chlorogenic acid | 92% | The role of seed extract of |
In a previous work, the authors have investigated the extract of plants, namely,
Aqueous extracts of
The inhibitive effect of the aqueous extract of Jasmin (
The inhibitive effects of aqueous extracts of
Ascorbic acid in combination with DQ-2000 (aminotrimethyl phosphonic acid) and DQ-2010 (1-hydroxyethylidine 1,1-diphosphonic acid) was used to reduce the concentration of zinc in the blowdown of the cooling systems. All the inhibitors used were found to be effective. The maximum inhibition efficiency 99.2% was obtained with DQ-2010 100 ppm + Ascorbic acid 200 ppm concentration. Inhibitors follow Langmuir isotherm which showed that they inhibit corrosion through adsorption [
In present work, authors have used the extract of (Kalmegh)
Plant extracts used by us as corrosion inhibitors.
S. no. | Plant used | Active constituents | Common name | Inhibition efficiency (%) |
---|---|---|---|---|
(A) | 96.7 | |||
(1) | Murrafoline-I | |||
(2) | Pyrayafoline-D | |||
(3) | Mahabinine-A | |||
(B) | 96.2 | |||
(1) | Skimmianine | |||
(C) | 98.1 | |||
(1) | Andrographolide | |||
(D) | 94.2 | |||
(1) | Ellagic acid | |||
(2) | Gallic acid | |||
(3) | Quercetin | |||
(4) | Cafeic acid | |||
(E) | 97.6 | |||
(1) | Karanjin | |||
(2) | Pongapine | |||
(3) | Kanjone | |||
(4) | Pongaglabrone | |||
(F) | Brucine | 98.2 | ||
(G) | 97.6 | |||
(1) | Piperine | |||
(2) | Piplartine | |||
(3) | Rutin | |||
(H) | 98.6 | |||
(1) | Arginine | |||
(I) | 89.6 | |||
(1) | Threonine | |||
(J) | 88.9 | |||
(1) | b-Sitosterol | |||
(K) | 88.8 | |||
(1) | Lanosterol | |||
(L) | 95.2 | |||
(1) | Bacoside A | |||
(2) | Bacoside B |
Prior to all measurements, the mild steel specimens, having composition (in wt%) 0.076 C, 0.012 P, 0.026 Si, 0.192 Mn, 0.050 Cr, 0.135 Cu, 0.023 Al, 0.050 Ni, and the remainder iron, were polished successively with fine grade Emery papers from 600 to 1200 grades. The specimens were washed thoroughly with double-distilled water and finally degreased with acetone and dried at room temperature. The aggressive solution 1 M HCl was prepared by dilution of analytical grade HCl (37%) with double-distilled water, and all experiments were carried out in unstirred solutions.
AC impedance (EIS) measurements and potentiodynamic polarization studies were carried out using a GAMRY PCI 4/300 electrochemical work station based on ESA 400. Gamry applications include EIS 300 (for EIS measurements) and DC 105 software (for corrosion) and Echem Analyst (5.50 V) software for data fitting. All electrochemical experiments were performed in a Gamry three-electrodes electrochemical cell under the atmospheric conditions with a platinum counter electrode and a saturated calomel electrode (SCE) as the reference electrode. The working electrode mild steel (7.5 cm long stem) with the exposed surface of 1.0 cm2 was immersed into aggressive solutions with and without inhibitor, and then the open circuit potential was measured after 30 minutes. EIS measurements were performed at corrosion potentials,
The leaves extract of
Electrochemical impedance and Tafel data at 308 K.
Name of inhibitor | Inhibitor concentration | ||||||
---|---|---|---|---|---|---|---|
1 M HCl | — | 8.5 | 68.9 | — | 446 | 1540.0 | — |
240.0 | 180.3 | 59.0 | 95.3 | 480 | 71.0 | 95.5 | |
300.0 | 256.2 | 58.2 | 96.6 | 469 | 48.0 | 96.9 | |
600.0 | 344.3 | 50.5 | 97.5 | 472 | 47.0 | 97.0 | |
200.0 | 101.9 | 59.2 | 91.7 | 457 | 159.0 | 89.3 | |
300.0 | 151.1 | 44.1 | 94.4 | 466 | 100.0 | 93.5 | |
400.0 | 264.8 | 30.7 | 96.7 | 499 | 60.0 | 96.0 | |
300.0 | 99.0 | 56.9 | 91.4 | 489 | 82.0 | 94.6 | |
600.0 | 108.0 | 52.4 | 92.1 | 462 | 59.0 | 96.1 | |
1200.0 | 491.0 | 40.4 | 98.2 | 486 | 30.6 | 98.0 |
Nyquist plots and Tafel plots for mild steel in 1 M HCl in the absence and presence of different inhibitors at their optimum concentration.
The higher inhibitive performance of
We have used seed extracts of
Electrochemical impedance, Tafel, and linear polarization resistance data at 308 K.
Name of inhibitor | Inhibitor concentration | ||||||
---|---|---|---|---|---|---|---|
1 M HCl | — | 8.5 | 68.9 | — | 446 | 1540.0 | — |
240.0 | 97.1 | 67.6 | 91.2 | 443 | 165.0 | 89.2 | |
300.0 | 117.5 | 56.1 | 92.7 | 462 | 98.0 | 93.5 | |
600.0 | 238.5 | 53.7 | 96.4 | 469 | 60.0 | 96.0 | |
300.0 | 129.5 | 39.6 | 92.9 | 461 | 84.0 | 94.0 | |
350.0 | 150.6 | 38.7 | 93.5 | 482 | 77.0 | 95.0 | |
400.0 | 239.8 | 35.7 | 96.5 | 471 | 49.0 | 97.0 | |
250.0 | 130.3 | 52.0 | 93.5 | 461 | 132.0 | 91.4 | |
300.0 | 159.9 | 47.1 | 94.7 | 463 | 97.0 | 93.7 | |
350.0 | 263.9 | 43.3 | 96.7 | 494 | 27.5 | 98.2 |
Nyquist plots and Tafel plots for mild steel in 1 M HCl in the absence and presence of different inhibitors at their optimum concentrations.
The best performance of
We have used fruits extract of
Electrochemical impedance, Tafel, and linear polarization resistance data at 308 K.
Name of inhibitor | Inhibitor concentration | ||||||
---|---|---|---|---|---|---|---|
1 M HCl | — | 8.5 | 68.9 | — | 446 | 1540.0 | — |
240.0 | 213.2.1 | 46.4 | 96.0 | 464 | 53.0 | 96.5 | |
300.0 | 273.3 | 33.1 | 96.9 | 469 | 46.0 | 96.9 | |
600.0 | 355.5 | 27.3 | 97.6 | 479 | 41.0 | 97.3 | |
200.0 | 215.0 | 43.0 | 96.0 | 503 | 59.0 | 96.1 | |
250.0 | 324.5 | 41.4 | 97.3 | 472 | 38.0 | 97.5 | |
300.0 | 644.9 | 32.4 | 98.6 | 493 | 28.0 | 98.1 | |
300.0 | 23.5 | 68.5 | 68.9 | 466 | 430.0 | 72.0 | |
600.0 | 58.2 | 65.4 | 85.4 | 515 | 212.0 | 86.2 | |
1200.0 | 65.2 | 56.3 | 87.0 | 464 | 160.0 | 89.6 |
Nyquist plots and Tafel plots for mild steel in 1 M HCl in the absence and presence of different inhibitors at their optimum concentrations.
Good performance of fruits extract as corrosion inhibitors for mild steel in 1 M HCl solutions may be due to the presence of heteroatoms,
Stem extracts of
Electrochemical impedance, Tafel, and linear polarization resistance data at 308 K.
Name of inhibitor | Inhibitor concentration | ||||||
---|---|---|---|---|---|---|---|
1 M HCl | — | 8.5 | 68.9 | — | 446 | 1540.0 | — |
300.0 | 17.0 | 67.4 | 50.5 | 478 | 785.0 | 49.0 | |
600.0 | 26.2 | 48.9 | 67.9 | 461 | 713.0 | 53.7 | |
1200.0 | 75.9 | 38.8 | 88.9 | 469 | 220.0 | 85.7 | |
300.0 | 28.7 | 63.9 | 70.7 | 444 | 407.0 | 54.0 | |
600.0 | 37.8 | 63.0 | 77.7 | 481 | 301.0 | 80.4 | |
1200.0 | 75.6 | 37.6 | 88.8 | 464 | 190.0 | 87.6 | |
240.0 | 41.9 | 53.5 | 79.9 | 464 | 518.0 | 66.3 | |
300.0 | 74.2 | 44.2 | 88.6 | 486 | 218.0 | 85.8 | |
600.0 | 175.2 | 39.4 | 95.2 | 489 | 75.0 | 95.1 |
Nyquist plots and Tafel plots for mild steel in 1 M HCl in the absence and presence of different inhibitors at their optimum concentrations.
All the studied plant extracts obtained from leaves, seeds, fruits, and stem showed good inhibition efficiency (>95%) at their optimum concentrations for mild steel in 1 M HCl. The optimum concentration is considered as a concentration beyond which increase in extract concentration showed no significant change in the inhibition efficiency. The good performance may be attributed to the synergism between the different compounds present in the extracts.
In acidic solutions, transition of the metal/solution interface is attributed to the adsorption of the inhibitor molecules at the metal/solution interface, forming a protective film. The rate of adsorption is usually rapid, and hence, the reactive metal surface is shielded from the acid solutions [
Generally, two modes of adsorption were considered. In one mode, the neutral molecules of leaves extract can be adsorbed on the surface of mild steel through the chemisorption mechanism, involving the displacement of water molecules from the mild steel surface and the sharing electrons between the heteroatoms and iron. The inhibitor molecules can also adsorb on the mild steel surface based on donor-acceptor interactions between
Since all the different parts of plant extract possess several heteroatoms containing active constituents, therefore there may be a synergism between the molecules accounting for the good inhibition efficiencies.
All the extracts studied showed good inhibition efficiency.
All the extracts were found to be the mixed type of inhibitors.
All the results obtained from EIS, LPR, and weight loss are in good agreement with each other.