Spirulina platensis

C. Kamal; M.G. Sethuraman

doi:10.1016/j.arabjc.2010.08.006

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Original article

5 (

); 155-161

doi:

10.1016/j.arabjc.2010.08.006

Spirulina platensis – A novel green inhibitor for acid corrosion of mild steel

C. Kamal, M.G. Sethuraman^*

Department of Chemistry, Gandhigram Rural Institute-Deemed University, Gandhigram 624 302, Tamil Nadu, India

*Corresponding author. Tel.: +91 (0) 451 2452371; fax: +91 (0) 451 2454466 mgsethu@rediffmail.com (M.G. Sethuraman)

Received: 2010-7-14, Accepted: 2010-8-5, Published: 2010-04-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Available online 11 August 2010

Abstract

The inhibition of the corrosion of mild steel in 1 M HCl and 1 M H₂SO₄ by Spirulina platensis has been studied at different temperatures viz., 303 K, 313 K and 323 K by weight loss method, potentiodynamic polarization method, electrochemical impedance spectroscopy measurements and SEM analysis. The inhibition efficiency increased with increasing concentration of the inhibitor in both HCl and H₂SO₄ media. The results of weight loss studies correlated well with those of impedance and polarization studies. From the results of weight loss studies at various temperatures, the mode of adsorption is confirmed to be physisorption. Further the adsorption has been found to follow Temkin isotherm. From this isotherm, the free energy of adsorption (ΔG) and entropy (ΔS) are calculated. The study reveals the corrosion inhibition potential of S. platensis in both the acid media, thus bringing to light another facet of this microalga as it has so far been used only to produce antioxidant principles, finding extensive use in medicine especially as neutraceutical.

Keywords

Green inhibitors

Corrosion inhibitors

Physisorption

Impedance

Polarization

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1 Introduction

Acids such as HCl and H₂SO₄ are widely used as pickling, descaling and cleaning agents in several industries for the removal of undesirable oxide films and corrosion products (Bothi Raja and Sethuraman, 2009a). In many industries, mild steel (MS) is the material of choice in the fabrication of reaction vessels, storage tanks etc., which get corroded easily in the presence of acids (Bothi Raja and Sethuraman, 2009b).

Among the methods of corrosion control, use of inhibitors is very popular due to the ease of application. Mostly, the heterocyclic compounds containing O, S and N as heteroatoms serve as good inhibitors for corrosion (Senthil Kumar et al., 2009). In view of the disadvantages of the compounds of synthetic origin, there has been an upsurge in screening of compounds of natural origin for their corrosion inhibition effect (Bothi Raja and Sethuraman, 2008). In the present study, a marine alga viz., Spirulina platensis is examined for its potential to control corrosion of MS in acid media.

S. platensis belongs to the family, Oscillatoriaceae which has several therapeutic properties such as hypocholesterolemic, immunological, antiviral and antimutagenic (Herrero et al., 2004; Aleisa, 2008; Belay et al., 1993 ). This alga is reported to contain amino acids such as methionine, γ-linolenic acid, peptides, proteins, carbohydrates and phycocyanins (Chamorro-Cevallosa et al., 2008). S. platensis finds use as an antioxidant especially for the production of nutraceuticals (Wang and Zhao, 2005). Further, it is widely used in food industries due to its rich protein content (Diraman et al., 2009; Rahman et al., 2006; Pelizer et al., 2003 ; http://www.nbent.com/spirulina.htm).

In the present study, the corrosion inhibitive property of S. platensis has been investigated in both HCl and H₂SO₄ media by weight loss method, electrochemical method as well as SEM analysis.

2 Experimental

2.1

2.1 Preparation of S. platensis sample

Powdered form of S. platensis (100 g) supplied by Ms. Sanat Food Products Pvt. Ltd., Kodai Road, Dindigul Dist., India was extracted with absolute ethanol using Soxhlet apparatus. The ethanolic extract was distilled to obtain a solid residue, which was used as the inhibitor. Then, the inhibitor was dissolved in 1 M HCl and 1 M H₂SO₄ separately and appropriately diluted to get solutions of desired concentrations.

2.2

2.2 Specimen preparation

MS specimens of the composition C = 0.07%, Mn = 0.34%, P = 0.08% and the remaining % of Fe were chosen for the present study. Mild steel specimens of the size 1.5 × 5.0 × 0.2 cm were used for weight loss studies, while coupons of size 1 cm² were used for electrochemical studies and SEM analysis. The specimens were well cleaned and then degreased with acetone, prior to use.

2.3

2.3 Weight loss study

The mechanically polished and preweighed mild steel specimens of uniform size were suspended in 100 ml test solutions with and without S. platensis at different concentrations for a period of 2 h at three different temperatures viz., 303 K, 313 K and 323 K. Then the specimens were washed, dried and weighed. From the weight loss data, the inhibition efficiency (IE) was calculated as follows (Bothi Raja and Sethuraman, 2009a),

(1)

IE (%) = \frac{W_{2} - W_{1}}{W_{1}} \times 100

where W₁ and W₂ are the weights of the MS coupons in presence and absence of inhibitor, respectively.

2.4

2.4 Electrochemical studies

The CHI electrochemical analyzer Model No. 650B was used to record Tafel polarization curve and impedance curve. MS plates served as working electrode while platinum and calomel electrodes were used as counter electrode and the reference electrode, respectively. The electrodes were immersed for 30 min to obtain steady state open circuit potential. Impedance measurements were carried out at E_corr potential at the range from 0.1 to 1000 Hz at an amplitude of 10 mV. The impedance diagrams are given in Nyquist representation (Bothi Raja and Sethuraman, 2009b). The impedance and polarization parameters such as double layer capacitance (C_dl), charge transfer resistance (R_ct), corrosion current (i_corr), corrosion potential (E_corr), anodic Tafel slope (b_a) and cathodic Tafel slope (b_c) were computed from the polarization curves and Nyquist plots (Bothi Raja and Sethuraman, 2009a).

The IE values were calculated from potentiodynamic polarization measurements using the Eq. (2),

(2)

IE (%) = \frac{I_{corr} - I_{corr (1)}}{I_{corr}} \times 100

where I_corr is the corrosion current without inhibitor and I_corr₍₁₎ is the corrosion current with inhibitor.

To obtain the double layer capacitance (C_dl), the frequency at which the imaginary component of the impedance is maximum, (−Z_max), is found and C_dl values are obtained from the equation:

(3)

f (- Z^{″} \max) = \frac{1}{2 π C_{dl} R_{ct}}

From a.c. impedance measurements, the IE values were calculated from the following relation,

(4)

IE = \frac{R_{ct (i)} - R_{ct (b)}}{R_{ct (i)}} \times 100

where

R_{ct (i)}

and

R_{ct (b)}

were the inhibited and uninhibited charge transfer values, respectively.

2.5

2.5 SEM images

For taking SEM images, the MS specimens were immersed in the solution without inhibitor as well as in the solution containing optimum concentration of inhibitor (500 ppm) separately for 2 h. Then, the specimens were removed and rinsed with rectified spirit quickly. The images were taken using HITACHI – Model S – 3000 H Scanning Electron Microscope.

3 Results and discussion

3.1

3.1 Weight loss study

The inhibition efficiency was obtained from weight loss measurements at different concentrations of inhibitor at various temperatures viz., 303 K, 313 K and 323 K in the usual way (Senthil Kumar et al., 2009). The variation in inhibition efficiency with concentration of the green inhibitor is shown in Table 1. From the values of Table 1, it is clear that the S. platensis effectively inhibits the corrosion rate of MS in both HCl and H₂SO₄ media with higher IE in H₂SO₄ medium. This is due to the availability of more sites on metal surface for adsorption in H₂SO₄ medium because of lesser adsorption of the sulphate ions on the metal surface (Ahamad and Quraishi, 2009).

Table 1 Effect of S. platensis on MS in acid media (weight loss studies).

S. No.	Concentration of inhibitor (ppm)	% of IE (in H₂SO₄)			% of IE (in HCl)
S. No.	Concentration of inhibitor (ppm)	303 K	313 K	323 K	303 K	313 K	323 K
1	100	54.62	48.98	41.42	50.56	48.88	37.41
2	200	60.32	52.72	44.88	56.81	51.68	41.98
3	300	70.04	62.99	53.64	66.29	56.17	52.29
4	400	76.39	68.89	59.52	68.38	65.16	57.63
5	500	82.65	73.54	64.57	74.15	70.79	61.45

Inhibition efficiency was found to increase with the concentration of inhibitor (Table 1), with maximum IE at a concentration of 500 ppm. The increase in inhibition efficiency is due to the increase in the number of constituent molecules of S. platensis adsorbed on the metal surface at higher concentrations (Zhang and Hua, 2009), so that the active sites of the metal are protected by the inhibitor molecules.

In both HCl and H₂SO₄ media, the inhibition efficiency decreased as the temperature increased. This may be due to the fact that constituents of inhibitor are adsorbed physically on the surface of the mild steel. The increase of the temperature might cause the desorption of the inhibitor constituents from the surface of the metal, due to the decrease in the strength of adsorption process at higher temperatures (Abboud et al., 2009).

3.2

3.2 Adsorption isotherms

The adsorption isotherms provide the basic information on the interaction between the green inhibitor and the mild steel surface (Senthil Kumar et al., 2009). The areas of surface coverage (θ) computed from the weight loss data were plotted against concentration to fit into Temkin isotherm (Figs. 1a and 1b).

Temkin isotherm of S. platensis on MS in 1 M H2SO4.

Temkin isotherm of S. platensis on MS in 1 M HCl.

From the slope of the Temkin isotherm, ΔG was calculated by the following relation (Bothi Raja and Sethuraman, 2009b),

(5)

Δ = - RT ln (55.5 K)

where R is universal gas constant in kJ mol⁻¹, 55.5 is a concentration of water in mol/L (Bouklah et al., 2006), T is the temperature and K is the equilibrium constant.

The negative values of ΔG (Table 2) in both the acids reflect a spontaneous adsorption of phytoconstituents of S. platensis on the surface of the MS (Bentiss et al., 2009). The ΔG values are less than −40 kJ mol⁻¹, which indicated that the molecules are physisorbed (De Souza and Spinelli, 2009) in the following ways.

Green inhibitor may be adsorbed through the donor (inhibitor)–acceptor (metal) interaction between the π-electrons and the unshared electron pairs of the heteroatoms of the constituents of S. platensis to make a bond with vacant d orbitals of the metal surface (Bothi Raja and Sethuraman, 2008) and
–NH₂ groups of amino acids present in S. platensis may be readily protonated in acid media by which, it might be adsorbed over the metal surface through negatively charged acid anions (Cl⁻, ${SO}_{4}^{2 -}$ ) (Bothi Raja and Sethuraman, 2008).

Table 2 Thermodynamic parameters for of S. platensis on MS in acid media.

S. No.	Medium	Temperature (K)	ΔG (kJ mol⁻¹)	ΔS (kJ mol⁻¹)
1	H₂SO₄	303	−12.02	8.2764
		313	−12.04	8.3521
		323	−12.06	8.3574
2	HCl	303	−11.99	8.2741
		313	−12.01	8.3512
		323	−12.05	8.3523

Further, the entropy (ΔS) is calculated by the following equation,

(6)

Δ S = \frac{Δ H - Δ G}{T}

where ΔG and ΔH are the free energy of adsorption and enthalpy, respectively, and T is the temperature.

3.3

3.3 Electrochemical studies

3.3.1

3.3.1 Potentiodynamic polarization

From the anodic and cathodic polarization curves (Figs. 2a and 2b) for S. platensis in 1 M HCl and H₂SO₄ media at different concentrations, various electrochemical parameters were computed and listed (Tables 3 and 4). From the i_corr values, the inhibition efficiency was calculated as in Eq. (2) (Senthil Kumar et al., 2009).

Tafel plots of S. platensis on MS in 1 M H2SO4.

Tafel plots of S. platensis on MS in 1 M HCl.

Table 3 Effect of S. platensis on MS in 1 M H₂SO₄ (polarization studies).

S. No.	Concentration of inhibitor (ppm)	b_a (mV dec⁻¹)	b_c (mV dec⁻¹)	E_corr (mV)	I_corr (μA cm⁻²)	% of IE
1	0	116.26	179.46	−0.4961	1192	–
2	100	105.21	154.51	−0.4593	678.22	43.01
3	200	66.35	122.98	−0.4572	315.24	73.55
4	300	64.97	119.11	−0.4561	256.57	78.48
5	400	60.64	116.25	−0.4536	218.96	81.63
6	500	59.41	116.13	−0.4502	214.61	81.99

Table 4 Effect of S. platensis on MS in 1 M HCl (polarization studies).

S. No.	Concentration of inhibitor (ppm)	b_a (mV dec⁻¹)	b_c (mV dec⁻¹)	E_corr (mV)	I_corr (μA cm⁻²)	% of IE
1	0	106.55	201.32	−0.4857	488.2	–
2	100	93.37	133.28	−0.4651	367.8	24.66
3	200	92.67	127.35	−0.4593	290.9	40.41
4	300	92.42	126.93	−0.4531	241.9	50.45
5	400	92.33	125.18	−0.4514	185.8	61.94
6	500	90.99	125.03	−0.4502	163.2	66.57

From Figs. 2a and 2b, it can be seen that, the inhibitor begins to desorb at a potential closer to −350 mV/SCE, which can be called as desorption potential. The similar behaviour has been obtained with other organic compounds (Lorenz and Mansfeld, 1981; Aksut et al., 1982; El Azar et al., 2002 ).

From the Tables 3 and 4, it is observed that the E_corr values were shifted slightly to the anodic region. Both the anodic and cathodic Tafel slope values decreased with the increase in the concentration of the inhibitor, thus indicating the mixed mode of inhibition with predominantly anodic type of inhibition (El-Etre et al., 2004).

This reveals that the green inhibitor reduces anodic dissolution along with the reduction of cathodic hydrogen evolution.

3.3.2

3.3.2 Impedance studies

The Nyquist plots for MS in both acid media as shown in Figs. 3a and 3b are not perfect semicircles, which is attributed to non-homogeneity of the surface and roughness of the metal (Bentiss et al., 2009). From the plots, it could be seen that impedance response of mild steel is increased by the addition of green inhibitor (Ahamad and Quraishi, 2009). For a corrosion system, the formation of double layer at metal/solution interface can be represented by the electronic equivalent circuit (Fig. 3c).

Nyquist plots of S. platensis on MS in 1 M H2SO4.

Nyquist plots of S. platensis on MS in 1 M HCl.

Equivalent circuit model for Nyquist plots.

The C_dl and R_ct values calculated from the Nyquist plots are listed in Tables 5 and 6.

Table 5 Effect of S. platensis on MS in 1 M H₂SO₄ (impedance studies).

S. No.	Concentration of inhibitor (ppm)	R_ct (Ω cm⁻²)	C_dl (μF cm⁻²)	% of IE
1	0	9.12	1765.22	–
2	100	17.18	436.58	46.91
3	200	36.09	252.99	74.72
4	300	37.2	246.17	75.41
5	400	45.11	245.93	79.77
6	500	46.93	240.53	80.21

Table 6 Effect of S. platensis on MS in 1 M HCl (impedance studies).

S. No.	Concentration of inhibitor (ppm)	R_ct (Ω cm⁻²)	C_dl (μF cm⁻²)	% of IE
1	0	24.48	93.26	–
2	100	31.43	88.23	22.11
3	200	49.72	85.28	50.76
4	300	80.32	83.58	69.52
5	400	87.53	81.97	72.03
6	500	101.25	80.42	75.82

The R_ct values increased with the increase of the concentration of inhibitor, which shows protection of MS surface by the inhibitor while the values of C_dl decreased with the increase in the concentration of inhibitor, which is due to the increase in the thickness of protective layer at higher concentrations (Xu et al., 2008; Elayyachy et al., 2006).

Inhibition efficiency, calculated from the values of R_ct (Eq. (3)) El-Etre et al., 2004, was found to be maximum at a concentration of 500 ppm of the inhibitor. The results of electrochemical studies were in good agreement with the results of gravimetric studies with slight deviations. This is due to the difference in immersion period of MS in the aggressive media (El-Etre et al., 2004).

3.4

3.4 SEM images

Scanning Electron Microscope (SEM) images were indicative of the changes that accompany the corrosion and protection on the MS surface of the mild steel (Figs. 4–6b ). Figs. 5a and 6a showed the damage caused to the surface by the acids, while Figs. 5b and 6b revealed the formation of a protective layer by the constituents of S. platensis.

SEM micrograph of the polished MS specimen.

SEM micrograph of MS in 1 M H2SO4 with green inhibitor (500 ppm).

SEM micrograph of MS in 1 M HCl with green inhibitor (500 ppm).

4 Conclusions

The following conclusions are drawn from the present study:

S. platensis inhibits the corrosion of mild steel in both HCl and H₂SO₄ media in a concentration dependent manner.
The inhibition efficiency is better in H₂SO₄ medium than in HCl medium.
S. platensis inhibits the corrosion through adsorption following Temkin isotherm. The values of ΔG were indicative of the physisorption.
The inhibitor altered both anodic and cathodic Tafel slopes, which showed the mixed mode of action of the inhibitor molecules.
The increase in R_ct values and decrease in C_dl values confirm the formation of an insulated protective layer over the mild steel surface, which was supported by SEM images.
The corrosion inhibitive effect shown by S. platensis can be correlated to the presence of phytoconstituents such as amino acids (methionine), fatty acids (γ-linolenic acid), peptides and proteins.

Acknowledgements

One of the authors (CK) is grateful to the UGC for the fellowship under Research Fellowship in Sciences for Meritorious Students. The authors are thankful to Dr. S. Abraham John, Asst. Professor of Chemistry, GRI, for providing instrumental facilities. Authors also thank the authorities of GRI for the encouragement.

References

Abboud Y., Abourriche A., Saffaj T., Berrada M., Charrouf M., Bennamara A., Hannache H., . A novel azo dye, 8-quinolinol-5-azoantipyrine as corrosion inhibitor for mild steel in acidic media. Desalination. 2009;237:175-189.
[Google Scholar]
Ahamad I., Quraishi M.A., . Bis (benzimidazol-2-yl) disulphide: An efficient water soluble inhibitor for corrosion of mild steel in acid media. Corros. Sci.. 2009;51:2006-2013.
[Google Scholar]
Aksut A.A., Lorenz W.J., Mansfeld F., . Determination of corrosion rates by electrochemical d.c. and a.c. methods – II. Systems with discontinuous steady state polarization behavior. Corros. Sci.. 1982;22:611-619.
[Google Scholar]
Aleisa A.M., . Cytological and biochemical effects of St. John’s Wort supplement (a complex mixture of St. John’s Wort, Rosemary and Spirulina) on somatic and germ cells of Swiss Albino mice. Int. J. Environ. Res. Pub. Health. 2008;5:408-417.
[Google Scholar]
Belay A., Ota Y., Miyakama K., Shimamatsu H., . Current knowledge on potential health benefits of Spirulina. J. Appl. Phycol.. 1993;5:235-241.
[Google Scholar]
Bentiss F., Jama C., Mernari B., El Attari H., El Kadi L., Lebrini M., Traisnel M., Lagren M., . Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole in normal hydrochloric acid medium. Corros. Sci.. 2009;51:1628-1635.
[Google Scholar]
Bothi Raja P., Sethuraman M.G., . Natural products as corrosion inhibitors for metals in corrosive media – a review. Mater. Lett.. 2008;62:113-116.
[Google Scholar]
Bothi Raja P., Sethuraman M.G., . Inhibition of corrosion of mild steel in sulphuric acid medium by Calotropis procera. Pig. Res. Tech.. 2009;38:33-37.
[Google Scholar]
Bothi Raja P., Sethuraman M.G., . Strychnos nux-vomica – an eco-friendly corrosion inhibitor for mild steel in 1 M sulfuric acid medium. Mater. Corros.. 2009;59:22-28.
[Google Scholar]
Bouklah M., Hammouti B., Lagrenee M., Bentiss F., . Thermodynamic properties of 2,5-bis(4-methoxyphenyl)-1,3,4-oxadiazole as a corrosion inhibitor for mild steel in normal sulfuric acid medium. Corros. Sci.. 2006;48:2831-2842.
[Google Scholar]
Chamorro-Cevallosa G., Garduno-Sicilianoa L., Barronb B.L., Madrigal-Bujaidarc E., Cruz-Vegad D.E., Pagese N., . Chemoprotective effect of Spirulina (Arthrospira) against cyclophosphamide-induced mutagenicity in mice. Food Chem. Toxicol.. 2008;46:567-574.
[Google Scholar]
De Souza F.S., Spinelli A., . Caffeic acid as a green corrosion inhibitor for mild steel. Corros. Sci.. 2009;51:642-649.
[Google Scholar]
Diraman H., Koru E., Digeklioglu H., . Fatty acid profile of Spirulina platensis used as a food supplement. Israeli J. Aquaculture. 2009;61:134-142.
[Google Scholar]
El Azar E., Traisnel M., Mernari B., Gengembre L., Bentiss F., Lagrenee M., . Electrochemical and XPS studies of 2,5-bis(n-pyridil)-1,3,4-thiadiazoles adsorption on mild steel in perchloric acid solution. Appl. Surf. Sci.. 2002;185:197-205.
[Google Scholar]
Elayyachy M., El Idrissi A., Hammouti B., . New thio-compounds as corrosion inhibitor for steel in 1 M HCl. Corros. Sci.. 2006;48:2470-2479.
[Google Scholar]
El-Etre A.Y., Abdallah M., El-Tantaury Z.E., . Corrosion inhibition of some metals using Lawsonia extract. Corros. Sci.. 2004;47:385-395.
[Google Scholar]
Herrero M., Ibanez E., Javier S., cifuenttes A., . Pressurized liquid extracts from Spirulina platensis microalga determination of their antioxidant activity and preliminary analysis by micellar electrokinetic chromatography. J. Chromatogr. A. 2004;1047:195-203.
[Google Scholar]
Lorenz W.J., Mansfeld F., . Determination of corrosion rates by electrochemical DC and AC methods. Corros. Sci.. 1981;21:647-672.
[Google Scholar]
Pelizer Lucia Helena, Danesi Eliane Dalva G., Rangel Carlota de O., Sassano Carlos E.N., Carvalho Joao Carles O., Sato Sunao, Moraes Iracema O., . Influence of inoculums age and concentration in Spirulina platensis. J. Food Eng.. 2003;56:371-375.
[Google Scholar]
Rahman M.H., Sikder M.H., Maidul Islam A.Z.M., Wahab M.A., . Spirulina as food supplement is effective in arsenicosis. Pakistan Assoc. Dermatologists. 2006;16:86-92.
[Google Scholar]
Senthil Kumar A.N., Tharini K., Sethuraman M.G., . Corrosion inhibitory effect of few piperidin-4-one oximes on mild steel in hydrochloric medium. Surf. Rev. Lett.. 2009;16:141-147.
[Google Scholar]
Wang Z.P., Zhao Y., . Morphological reversion of Spirulina (arthrospira) platensis (Cyanophyta): from linear to helical. J. Phycol.. 2005;41:622-628.
[Google Scholar]
Xu F., Duan J., Zang S., Hou B., . The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative. Mater. Lett.. 2008;62:4072-4074.
[Google Scholar]
Zhang Q.B., Hua Y.X., . Corrosion inhibition of mild steel by alkyl-imidazolium ionic liquids in hydrochloric acid. Electrochim. Acta. 2009;54:1881-1887.
[Google Scholar]

Introduction

Experimental

Preparation of S. platensis sample
Specimen preparation
Weight loss study
Electrochemical studies
SEM images

Results and discussion

Weight loss study
Adsorption isotherms
Electrochemical studies
SEM images

Conclusions

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[1] Abboud Y., Abourriche A., Saffaj T., Berrada M., Charrouf M., Bennamara A., Hannache H., . A novel azo dye, 8-quinolinol-5-azoantipyrine as corrosion inhibitor for mild steel in acidic media. Desalination. 2009;237:175-189.
[Google Scholar]

[2] Ahamad I., Quraishi M.A., . Bis (benzimidazol-2-yl) disulphide: An efficient water soluble inhibitor for corrosion of mild steel in acid media. Corros. Sci.. 2009;51:2006-2013.
[Google Scholar]

[3] Aksut A.A., Lorenz W.J., Mansfeld F., . Determination of corrosion rates by electrochemical d.c. and a.c. methods – II. Systems with discontinuous steady state polarization behavior. Corros. Sci.. 1982;22:611-619.
[Google Scholar]

[4] Aleisa A.M., . Cytological and biochemical effects of St. John’s Wort supplement (a complex mixture of St. John’s Wort, Rosemary and Spirulina) on somatic and germ cells of Swiss Albino mice. Int. J. Environ. Res. Pub. Health. 2008;5:408-417.
[Google Scholar]

[5] Belay A., Ota Y., Miyakama K., Shimamatsu H., . Current knowledge on potential health benefits of Spirulina. J. Appl. Phycol.. 1993;5:235-241.
[Google Scholar]

[6] Bentiss F., Jama C., Mernari B., El Attari H., El Kadi L., Lebrini M., Traisnel M., Lagren M., . Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole in normal hydrochloric acid medium. Corros. Sci.. 2009;51:1628-1635.
[Google Scholar]

[7] Bothi Raja P., Sethuraman M.G., . Natural products as corrosion inhibitors for metals in corrosive media – a review. Mater. Lett.. 2008;62:113-116.
[Google Scholar]

[8] Bothi Raja P., Sethuraman M.G., . Inhibition of corrosion of mild steel in sulphuric acid medium by Calotropis procera. Pig. Res. Tech.. 2009;38:33-37.
[Google Scholar]

[9] Bothi Raja P., Sethuraman M.G., . Strychnos nux-vomica – an eco-friendly corrosion inhibitor for mild steel in 1 M sulfuric acid medium. Mater. Corros.. 2009;59:22-28.
[Google Scholar]

[10] Bouklah M., Hammouti B., Lagrenee M., Bentiss F., . Thermodynamic properties of 2,5-bis(4-methoxyphenyl)-1,3,4-oxadiazole as a corrosion inhibitor for mild steel in normal sulfuric acid medium. Corros. Sci.. 2006;48:2831-2842.
[Google Scholar]

[11] Chamorro-Cevallosa G., Garduno-Sicilianoa L., Barronb B.L., Madrigal-Bujaidarc E., Cruz-Vegad D.E., Pagese N., . Chemoprotective effect of Spirulina (Arthrospira) against cyclophosphamide-induced mutagenicity in mice. Food Chem. Toxicol.. 2008;46:567-574.
[Google Scholar]

[12] De Souza F.S., Spinelli A., . Caffeic acid as a green corrosion inhibitor for mild steel. Corros. Sci.. 2009;51:642-649.
[Google Scholar]

[13] Diraman H., Koru E., Digeklioglu H., . Fatty acid profile of Spirulina platensis used as a food supplement. Israeli J. Aquaculture. 2009;61:134-142.
[Google Scholar]

[14] El Azar E., Traisnel M., Mernari B., Gengembre L., Bentiss F., Lagrenee M., . Electrochemical and XPS studies of 2,5-bis(n-pyridil)-1,3,4-thiadiazoles adsorption on mild steel in perchloric acid solution. Appl. Surf. Sci.. 2002;185:197-205.
[Google Scholar]

[15] Elayyachy M., El Idrissi A., Hammouti B., . New thio-compounds as corrosion inhibitor for steel in 1 M HCl. Corros. Sci.. 2006;48:2470-2479.
[Google Scholar]

[16] El-Etre A.Y., Abdallah M., El-Tantaury Z.E., . Corrosion inhibition of some metals using Lawsonia extract. Corros. Sci.. 2004;47:385-395.
[Google Scholar]

[17] Herrero M., Ibanez E., Javier S., cifuenttes A., . Pressurized liquid extracts from Spirulina platensis microalga determination of their antioxidant activity and preliminary analysis by micellar electrokinetic chromatography. J. Chromatogr. A. 2004;1047:195-203.
[Google Scholar]

[18] Lorenz W.J., Mansfeld F., . Determination of corrosion rates by electrochemical DC and AC methods. Corros. Sci.. 1981;21:647-672.
[Google Scholar]

[19] Pelizer Lucia Helena, Danesi Eliane Dalva G., Rangel Carlota de O., Sassano Carlos E.N., Carvalho Joao Carles O., Sato Sunao, Moraes Iracema O., . Influence of inoculums age and concentration in Spirulina platensis. J. Food Eng.. 2003;56:371-375.
[Google Scholar]

[20] Rahman M.H., Sikder M.H., Maidul Islam A.Z.M., Wahab M.A., . Spirulina as food supplement is effective in arsenicosis. Pakistan Assoc. Dermatologists. 2006;16:86-92.
[Google Scholar]

[21] Senthil Kumar A.N., Tharini K., Sethuraman M.G., . Corrosion inhibitory effect of few piperidin-4-one oximes on mild steel in hydrochloric medium. Surf. Rev. Lett.. 2009;16:141-147.
[Google Scholar]

[22] Wang Z.P., Zhao Y., . Morphological reversion of Spirulina (arthrospira) platensis (Cyanophyta): from linear to helical. J. Phycol.. 2005;41:622-628.
[Google Scholar]

[23] Xu F., Duan J., Zang S., Hou B., . The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative. Mater. Lett.. 2008;62:4072-4074.
[Google Scholar]

[24] Zhang Q.B., Hua Y.X., . Corrosion inhibition of mild steel by alkyl-imidazolium ionic liquids in hydrochloric acid. Electrochim. Acta. 2009;54:1881-1887.
[Google Scholar]