Allium Sativum ( Garlic ) Extract as Nontoxic Corrosion Inhibitor

e inhibition efficiency (IE) of an aqueous extract of garlic in controlling corrosion of carbon steel in well water in the absence and presence of Zn has been evaluated by mass-loss method. e formulation consisting of 2mL of garlic extract and 25 ppm Zn offers 70% inhibition efficiency to carbon steel immersed in well water. Polarization study reveals that this formulation controls the anodic reaction predominantly. FTIR spectra reveal that the protective �lm consists of Fe-allicin complex and Zn(OH)2.


Introduction
Environmental friendly inhibitors have attracted several researchers.Natural products are nontoxic, biodegradable, and readily available.ey have been used widely as inhibitors.Natural products such as caffeine [1,2] have been used as inhibitors.Corrosion inhibition of steel by plant extracts in acidic media has been reported [3,4].Scale inhibiting nature of plant extracts for various kinds of metals are summarized brie�y [5].Aqueous extract of Rosemary leaves [6], Zanthoxylum alatum [7], and Lawsonia [8] have been used to inhibit corrosion of metals.Corrosion inhibition of iron in hydrochloric acid solutions by naturally occurring henna has been investigated [9].Corrosion inhibition of carbon steel in low chloride media by an aqueous extract of Hibiscus rosasinensis Linn has been evaluated [10].Corrosion inhibition investigation of natural inhibitors is particularly interesting because they are nonexpensive, ecologically friendly, and possess no threat to the environment.e present work is undertaken: (i) to evaluate the inhibition efficiency (IE) of an aqueous extract of garlic in controlling the corrosion of carbon steel in well water in the absence and presence of Zn 2+ (ii) to analyze the protective �lm formed on the carbon steel by FTIR spectra, (iii) to understand the mechanistic aspects of corrosion inhibition by potentiodynamic polarization study, (iv) and to propose a suitable mechanism for corrosion inhibition.with Clarke's solution [11].e inhibition efficiency (IE) was then calculated using the following equation:

Experimental Procedure
where  1 is the corrosion rate in the absence of the inhibitor, and  2 is the corrosion rate in the presence of the inhibitor.

Surface Examination
. e carbon steel specimens were immersed in various test solutions for a period of 3 days, taken out and dried.e nature of the �lm formed on the surface of metal specimens was analyzed by FTIR spectroscopic study.

Potentiodynamic Polarization.
Polarization studies were carried out in an H&CH electrochemical work station impedance analyzer model CHI 660A.A three-electrode cell assembly was used.e working electrode was carbon steel.A saturated calomel electrode (SCE) was used as the reference electrode, and a rectangular platinum foil was used as the counter electrode.
2.6.FTIR Spectra.FTIR spectra were recorded in a Perkin-Elmer 1600 spectrophotometer.e �lm was carefully removed, mixed thoroughly with KBr, made into pellets, and FTIR spectra were recorded.

Analysis of Polarization
Curves.e potentiodynamic polarization curves of carbon steel immersed in well water in the absence and presence of inhibitors are shown in Figures 1(a) and 1(b).e corrosion parameters are given in Table 3.When carbon steel is immersed in well water the corrosion potential is −704 mV versus SCE (saturated calomel electrode).e corrosion current is 2.600 × 10 −6 A/cm 2 .When 2 mL of garlic extract and 25 ppm of Zn 2+ are added to the above system, the corrosion potential shied to the anodic side (−690 mV versus SCE).is suggests that this formulation controls the anodic reaction predominantly.In the presence of the inhibitor system, the corrosion current decreases from 2.600 × 10 −6 A/cm 2 to 2.353 × 10 −6 A/cm 2 .is suggests the inhibitive nature of this inhibitor system [14,15].

Analysis of FTIR Spectra. e active principle in an aqueous extract of garlic is allicin. It consists of S=O and S group.
A few drops of an aqueous extract of garlic were dried on a glass plate.A solid mass was obtained.Its FTIR spectrum is shown Figure 2(a).Vinyl group appeared at 1026.28 cm −1 .S=O appeared at 1026 cm −1 and S at 1237.58 cm −1 .us the structure of allicin is con�rmed by FTIR spectra (Scheme 1) [16].e FTIR spectrum of complex prepared by mixing garlic extract and Zn 2+ is shown in Figure 2(b).e band due to conjugated double bonds shis from 3757.23 cm −1 to 3819.62 cm −1 .e band at 608.46 corresponds to Zn-O stretching.e OH stretching frequency appears at 3407.06 cm −1 .is con�rms the formation of Zn(OH) 2 on the cathodic sites of the metal surface [17][18][19].Since there is complete coordination between Fe 2+ and allicin, the band due to the formation of the complex gets vanished in the FTIR spectrum of the �lm formed on the surface of carbon steel by garlic extract (Figure 2(b)) [20,21].

Mechanism of Corrosion Inhibition.
Mass-loss study reveals that the formulation consisting of 2 mL of garlic extract +25 ppm of Zn 2+ offers 70% IE to carbon steel immersed in well water.Polarization study reveals that this formulation controls the anodic reaction predominantly.FTIR spectra reveal that the protective �lm consists of Fe 2+allicin complex and Zn(OH) 2 .In order to explain the above facts in a holistic way, the following mechanism of corrosion inhibition is proposed.
(i) When the formulation consisting of well water, garlic extract, and Zn 2+ is prepared, there is formation of Zn 2+ -allicin complex in solution.
(ii) When carbon steel is immersed in the solution, the Zn 2+ -allicin complex diffuses from the bulk of the solution towards the metal surface.(iii) On the metal surface, Zn 2+ -allicin complex is converted into Fe 2+ -allicin complex.Zn 2+ is released.

Conclusions
e present study leads to the following conclusions: (i) the formulation consisting of 2 mL garlic extract and 25 ppm of Zn 2+ offers 70% inhibition efficiency to carbon steel immersed in well water; (ii) polarization study reveals that this formulation controls the anodic reaction predominantly; (iii) FTIR spectra reveal that the protective �lm consists of Fe 2+ -allicin complex and Zn(OH) 2 .

F 2 :
(a) FTIR spectra of solid mass obtained by evaporating the garlic extract.(b) FTIR spectra of �lm formed on surface of the carbon steel specimen aer immersion in well water containing 2 mL of garlic extract and 25 ppm of Zn 2+ .
[12,13]on rate (CR) of carbon steel immersed in well water in the absence and presence of inhibitors and the inhibition efficiency (IE) obtained by mass-loss method.Immersion period: 3 days; inhibitor: garlic extract + Zn 2+ .given in the Table.It is seen from Table2that the aqueous extract of garlic is a good inhibitor to carbon steel in well water.2mL of garlic shows 50% IE.As concentration of garlic extract increases, IE also increases.atis,athigherconcentrations,garlicaccelerates corrosion inhibition[12,13].3.1.1.In�uence of �n 2+ on the Inhibition Efficiency of GarlicExtract.e in�uence of Zn 2+ on the IE of garlic extract is given in Table2.In the presence of Zn 3.1.Analysis of Results of Mass-LossMethod.ecorrosionrate(CR) of carbon steel immersed in well water (whose composition is given in Table1) in the absence and presence of inhibitor systems is given in Table2.e inhibition T 2: 2+ (25 ppm), excellent inhibitive property is shown by garlic extract.For example, 2 mL of garlic extract accelerate corrosion of carbon steel (IE = 50%); 25 ppm of Zn 2+ have 20% IE, but their combination has 70%.