Inhibitive Properties of MB – Zn²⁺ System and Its Synergism With SPT

Inhibitive Properties of MB – Zn²⁺ System and Its Synergism With SPT

Y. Brightson Arul Jacob1, J. Jeyasundari 1,*, R. Sayee Kannan2

1Department of Chemistry, NMSSVN College, Madurai-625019, Tamilnadu, India.

2Department of Chemistry, Thiagarajar College, Madurai-625009, Tamilnadu, India.

Abstract

The Inhibition Efficiency (IE) of Methylene Blue (MB) Zn2+ system in controlling corrosion of carbon steel immersed in an aqueous solution has been evaluated by weight loss method. The formulation consisting of 250 ppm of MB and 25 ppm of Zn2+ has 84% inhibition efficiency (IE). The influence of SPT (Sodium Potassium Tartrate) on the IE of MB Zn2+ system has been studied. 250 ppm of MB -25 ppm of Zn2+ and 250 ppm of SPT has 94% inhibition efficiency (IE). Electro Chemical studies such as Potentiodymanic polarization and AC impedance have been used to find the mechanic aspects of corrosion inhibition.

Keywords:

Carbon steel, Corrosion inhibition, Methylene Blue (MB), Sodium Potassium Tartrate(SPT), AC impedance spectra, Potentio dynamic Polarization study.

1. Introduction

Several compounds such as molybdate [1,2], Phosphonic acids [3], Poly acryl amide [4] and Caffeine [5,6] have been used as corrosion inhibitions. Corrosion inhibition of mild steel in acidic media by some organic dyes has been investigated [7]. Qguzie has studied the inhibition of corrosion of mild steel in hydrochloric acid solution by methylene blue dye [8].Eriochrome black T serves as a good corrosion inhibitor for carbon steel in well water [9]. At pH 11 methyl orange along with Zn2+ functions as a good inhibitor in controlling corrosion of Aluminum [10]. However, the stability of the inhibitor lm formed over the metal surface depends on some physicochemical properties of the molecule, related to its functional groups, aromaticity, the possible steric effects, elec-tronic density of donors, type of the corrosive medium and nature of the interaction between the inhibitors with the d -orbital vacant of iron [11-12]. The present work is represent and studies the influence on the corrosion inhibition of mild steel in aqueous solution, of methylene blue dye (MB) which acts as a good inhibitor

2. Experimental

1. Preparation of specimens

   Mild steel specimens were chosen from the same sheet of the following composition 0.1 percent C, 0.026 percent S, 0.06 percent P, 0.4 percent Mn and the balance Fe. Mild steel specimen of the dimensions 1.0×4.0x0.2 cm were polished to mirror trichloro ethylene and used for mass loss and surface examinations studies.

2. Weight loss study

   The weighed specimen in triplicate were suspended by means of glass hooks in 100ml beakers containing 100ml of double distilled water in various concentration of inhibitors in the presence and absence of Zn2+ for 3 days of immersion. After 3days of immersion the specimens were taken out, washed in running water dried and weighed. From the change in weights of the specimen corrosion rates were calculated using the following relationship.

   Loss in weight (mg)

   Corrosion rate = (1)

   Surface area of the specimen (dm2) × Period of immersion (days)

   Corrosion inhibition efficiency (IE) was then calculated using the equation IE = 100[1-W2 / W1] % (2)

   Where W1=corrosion rate in the absence of the inhibitors and W2=corrosion rate in the presence of the inhibitors

3. Electrochemical study

   Polarization studies carried out in a CHI electrochemical workstation with impedance, Model 660 A, a three electrode cell assembly was used. Saturated calomel electrode (SCE) was the reference electrode and platinum was the counter electrode from the polarization study, corrosion parameters such as corrosion potential (Ecorr), corrosion current (I corr) and tafel slopes (anodic= ba and cathodic = bc) were calculated.

4. AC impedance measurements

EG and G electrochemical impedance analyzer model 6310 was used to record AC impedance measurements. A three electrode cell assembly was used. The working electrode was a rectangular specimen of carbon steel with one face of the electrode of constant 1 cm2 area exposed. A rectangular platinum foil was used as the counter electrodes. A time interval of 5 to 10 minutes was given for the system circuit potential. There over this steady state potential an AC potential of 10mV was superimposed. The AC frequency was varied from 100MHz to KHz. the real part (Z) and imaginary part (Z) of the cell impedance were measure in ohm for various frequencies. The Rt (Charge transfer resistance) and Cdl (double layer capacitance) values were calculated. Cdl values were calculated using the following relationship.

1

Cdl= (3)

2×3.14× fmax×Rt

3. Results and Discussion

1. Weight loss study

   The corrosion inhibition efficiencies (IE) of MB (Methylene Blue) in controlling the corrosion of carbon steel immersed in aqueous solution 60 ppm Cl- in the absence and presence of zinc ion. The influence of SPT (Sodium Potassium Tartrate) on MB Zn2+ was studied and IE was found to 94%. The values indicates that the ability of MB- Zn2+ – SPT as a good corrosion inhibition. The values are given in table (1-3) Corrosion rates (CR) of carbon steel in aqueous

   solution in the absence and presence of inhibitors and the efficiencies obtained by weight loss method.

   Table 1. Corrosion rates (CR mdd) carbon steel immersed in an aqueous solution containing 60 ppm of Cl- and the inhibition efficiencies (IE) obtained by weight loss method.

   Immersion period Three days

   MB ppm	Zn2+ ppm	CR mdd	IE %
   0	0	17.27	–
   50	0	15.45	32
   100	0	11.82	48
   150	0	9.09	60
   200	0	7.27	68
   250	0	6.36	72

   Table 2. Corrosion rates (CR mdd) carbon steel immersed in an aqueous solution containing 60 ppm of Cl- and the inhibition efficiencies (IE) obtained by weight loss method

   MB ppm	Zn2+ ppm	CR mdd	IE %
   50	25	18.18	20
   100	25	13.63	52
   150	25	8.18	64
   200	25	5.45	76
   250	25	3.63	84

   Table 3. Corrosion rates (CR mdd) carbon steel immersed in an aqueous solution containing 60 ppm of Cl- and the inhibition efficiencies (IE) obtained by weight loss method

   MB ppm	Zn2+ ppm	SPT ppm	CR mdd	IE %
   50	25	250	15.90	30
   100	25	250	10.00	56
   150	25/p>	250	5.90	74
   200	25	250	2.72	88
   250	25	250	1.36	94

   MB 250 ppm alone has inhibition efficiency 72% increasing the concentration of Zn2+ shown the increasing efficiency. 250 ppm of Methylene Blue (MB) and 25 ppm of Zn2+ has 84% of inhibition efficiency (IE).

2. Influence of SPT on the inhibition efficiency of MB-Zn2+ system

   It is observed that when SPT is added the inhibition efficiency of MB Zn2+ system increases. The increase in IE is more pronounced at 250 ppm of SPT. Synergistic effect exists between MB- Zn2+ system and SPT 250 ppm of MG alone has 74% inhibition efficiency (IE). 250 ppm of Methylene Blue (MB) and 100 ppm of Zn2+ has 84% IE. 250 ppm of SPT is added their combination has 94% IE. (Table 1-4).

3. Analysis of Potentio dynamic Polarization Curves.

   Polarization study has been used to study the formation of protective film on the metal surface. The potentio dynamic polarization curves of carbon steel immersed in an aqueous solution in the absence and presence of inhibitor are shown Figure 1.

   The corrosion parameters namely corrosion potential (Ecorr) Tafel slopes bc and ba linear polarization resistance (LPR) and corrosion current (Icorr) are given in table 4. It is observed figure (1) that when carbon steel immersed in an aqueous solution, the corrosion potential is -578mV Vs SCE (Saturated Calomel Electrode). The LPR value is 1.46 x10-3ohm cm2. The corrosion current value is

   4.293 x 10 -5 A /cm2.

   When 250 ppm of Methylene Blue (MB), 25 ppm of Zn2+, 250 ppm of SPT are added to the above environment the corrosion potential is shifted to the noble side due to the formation of protective film on the metal surface. There is not much change in the value of anodic Tafel slopes (221 and 124 mv/decade).But there is slight change in the anodic Tafel slope (415 and 296 mv/decade).

   Hence MB Zn2+ – SPT system functions as mixed inhibitor. It is observed from table-4. The LPR value was increases and the corrosion current decreases. These observations suggest the formation of protective film on the metal surface.

   Table 4. corrosion parameters of carbon steel immersed in aqueous solution obtained from Potentiodymanic polarization study

   System	Ecorr	ba mv / dec	bc mv / dec	LPR ohm cm2	Icorr A / cm2
   Aqueous solution (Blank)	-578	415	221	1.46×10-3	4.293×10-5
   Aqueous solution containing MB(250ppm) + Zn2+(100ppm)+SPT (250 ppm)	-411	296	124	8.67 x10-4	4.389×10-7

   Figure 1. Polarization curves of mild steel immersed in various test solutions

   1. Aqueous solution (Blank) b) MB (250 ppm) + Zn2+ (25 ppm) + SPT (250 ppm)

4. Analysis of AC impedance spectra

AC impedance spectra of carbon steel in aqueous solution in the absence and presence of inhibitors are shown in Fig (2) (Nyquist plot) Fig (3) (Bode plots).

The corrosion parameters namely charge transfer resistance (Rt) and double layer capacitance (Cdl) derived from Nyquist plots are given in table-5.

The impedance log (Z/ohm) values derived from bode plots are also given in table-5.

It is observed that when carbon steel immersed in an aqueous solution, the Rt value is

48 ohm cm2. The (Cdl) value is 1.19 x 10-8 MF/cm2.The impedance [log (Z/ohm ] is 2.683.

When inhibitors 250 ppm of Methylene Blue (MB),25 ppm of Zn2+, 250 ppm of SPT are added the Rt value increases from 428 to 1326 ohm cm2. The Cdl value decreases from 1.19 x10-8 to 0.384 x 10-8 MF/cm2. The

impedance value increases from 2.683 to 3.939. This observation suggests that a protective film is formed on the metal surface.

Table 5. AC impedance parameters of carbon steel immersed in an aqueous solution and inhibitors

System	Rt ohm cm2	Cdl F/cm2	Impedance (log Z/ohm)
Aqueous solution (Blank)	428	1.19 x 10-8	2.683
Aqueous solution containing MB(250ppm) + Zn2+(25 ppm) +SPT (250 ppm)	1326	0.3842 x 10-8	3.939

Figure 2. AC impedance spectra of mild steel immersed in various test solutions (Nquist Plot)

1. Aqueous solution (Blank)

2. MB (250 ppm) + Zn2+ (25 ppm) + SPT (250 ppm)

   Figure 3a. AC impedance spectra of mild steel immersed in various test solutions (Bode Plot)

   1. Aqueous solution (Blank)

Figure 3b. AC impedance spectra of mild steel immersed in various test solutions (Bode Plot)

a) MB (250 ppm) + Zn2+(25 ppm) + SPT(250 ppm)

4. Conclusion

The results of the weight loss study shows that the formulation consisting of 250 ppm of Methylene Blue (MB) and 25 ppm of Zn2+, 250ppm of SPT has 94% inhibition efficiency (IE) in controlling corrosion of carbon steel in an aqueous solution. A synergetic effect exists between Zn2+ and Methylene Blue (MB) and SPT.

Polarization study reveals that, this formulation function as anodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface.

When the aqueous solution contains 250 ppm of Methylene Blue (MB), 25 ppm of Zn2+ and 250 ppm of SPT is prepared there is formulation of Zn2+-MB and Zn2+-SPT complex in solution.

When carbon steel is immersed in this solution Zn2+-MB and Zn2+-SPT complex diffuses from the bulk of the solution towards metal surface.

On the metal surface Zn2+-MB-SPT complex is converted in to Fe2+-MB, Fe2+-SPT complex on the anodic sites. Zn2+ is released.

Zn2+-MB, Zn2+-SPT+Fe2+ Fe2+-MB,Fe2+-SPT +Zn2+.

The released Zn2+ combines with OH- to form Zn(OH)2 on the cathodic sites.

Zn2+ + 2OH- Zn(OH)2

5.References

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