Original Article
Int. J. Chem. Sci, Volume: 16( 2)

Nio-PANI Composite as Potential Inhibitor for Mild Steel in Acidic Corrosion Environment

*Correspondence:
Kamatchi Selvaraj P , Department of Chemistry, Govt. Arts College for Men (AUT), Nandanam, Chennai, Tamil Nadu, India, Tel: 9444568678; E-mail: [email protected]

Received: May 04, 2018; Accepted: May 17, 2018; Published: May 23, 2018

Citation: Kamatchi Selvaraj P, Sivakumar S, Selvaraj S. Nio-PANI Composite as Potential Inhibitor for Mild Steel in Acidic Corrosion Environment. Int J Chem Sci. 2018;16(2):268.

Abstract

Oxidative polymerization of aniline along with NiO nanoparticles using APS as oxidant and DBSA as dopant as well as surfactant at 0ºC yielded water soluble NiO-polyaniline composite. Spectral analysis like FTIR, XRD and SEM confirms the formation of the composite. Potentiality against corrosion is tested by gravimetric method, open circuit potential measurement, potentiodynamic polarization and electrochemical impedance spectroscopy. Effectiveness to give protection up to eight hours with slight changes in efficiency is observed in weight loss method. The results expose that the materials synthesized could give safe working environment in industrial maintenance work.

Keywords

NiO-PANI; Mild steel; OCP; Potentiodynamic polarization; EIS

Introduction

Corrosion, a spontaneous process of deterioration of metallic materials by the environment, reflect impact on economic losses and safeties. Apart from the natural commodities, human activities also initiate corrosion. Industrial maintenance work like acid descaling and acid pickling dissolves the machinery parts and reduces their life time. Inhibitors are widely employed for prophylactic action on metal parts [1-3]. The polar functional groups and π-electrons present in the organic inhibitors act as adsorption site for metal-inhibitor interaction [4-6].

The adsorption may be physical due to electrostatic force of attraction between the inhibitors and substrate surface or chemical ascribable to dispense of electrons among inhibitors and metal or both [7,8]. Conducting polymers have been studied extensively in the place of organic compounds owing to their stability and mechanical strength [9,10]. Polyaniline has been explored as good protective abettor against deterioration of metal [11-13]. Pseudocapacitive electrodes have been developed from various transition metal oxides including NiO [14]. Further nickel oxide is used in electrochromic coating [15], as a catalyst [16], as an adhesive in enamels [17] and as an anode layer in solid oxide fuel cells [18]. The above applications of NiO encourages to incorporate it with PANI to improve the inhibition efficiency of PANI. The present paper focuses on the synthesis of water soluble NiO-PANI composite and its competency against corrosion of mild steel in acidic environment.

Materials and Instrumentation

Materials

Analytical grade aniline purchased from Merck Industries was purified by distillation with zinc dust before it was used for synthesis. Hydrochloric acid, polyethylene glycol, Nickel chloride, oxalic acid, ammoniumperoxydisulphate (APS) and sodium salt of dodecyl benzene sulphonic acid (DBSA) chemicals with AR grade purchased from Merck Industries were used without purification.

Instrumentation

The synthesized composite was characterized by recording the FTIR spectrum (Perkin-Elmer 337 spectrometer) in the frequency range of 4000-450 cm-1 using KBr pellets. Rigaku Maniflex diffractometer (Japan) was used to record the XRD and JSM-6390 Scanning Electron Microscope was adopted to analyze the morphology of the composite. Using ECLAB 10.37 model, EIS and potentiodynamic polarization studies were recorded. CHI electrochemical analyzer instrument 1200B model was used to measure OCP values.

Experimental

Synthesis of Nickel Oxide-Polyaniline composite

The nickel oxide nanoparticles were prepared by the procedure reported in the literature [19]. NiO-Polyaniline composite was synthesized by in-situ chemical oxidative polymerization method [20]. To 100 ml of aqueous solution containing 1 ml of 0.1 M aniline and 3 ml of 0.1 M HCl, another solution, which was prepared by dispersing required amount nickel oxide in 0.1 M DBSA using ultrasonic waves of 42 kHz oscillation frequency for 45 minutes, was added. The mixture was kept at 0°C with constant stirring for 4 hours along with the drop wise addition 100 ml of 0.1 M APS solution. The reaction mixture was kept aside for 24 hours. Green colored precipitate obtained was filtered, washed with double distilled water and acetone for several times sequentially and dried in hot air oven for 24 hours.

Results and Discussion

Characterization of NiO-PANI composite

FTIR analysis: The FTIR spectrum of nickel oxide (FIG. 1a) contains peak around 470 cm-1 due to Ni-O stretching vibration and a broad peak around 3500 cm-1 due to -OH vibration of water molecule [21]. The absorption bands of PANI (FIG. 1b) at 1562 cm-1 and 1443 cm-1 due to nitrogen-quinonoid ring structure and other peaks at 1739 cm-1, 1230 cm-1 and 1033 cm-1 are matches very well with the reported values [22].

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Figure 1a: FTIR spectra of NiO.

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Figure 1b: FTIR spectra of PANI.

The characteristic peaks shown in FTIR spectrum of NiO-PANI composite (FIG. 1c) at 3450 cm-1, 2922 cm-1, 1735 cm-1, 1036 cm-1 ascribable to O-H vibration, C-H and N-H stretching respectively. The shift observed towards higher frequency region than the reported value [23] might be due to the changes adopted in the preparation to make the composite water soluble.

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Figure 1c: FTIR spectra of NiO-PANI composite.

XRD analysis of PANI and NiO-PANI composite: The XRD of NiO-PANI composite (FIG. 2a and 2b) shows peaks around 38°, 44°, 63°, 75° and 79°. These peaks were assigned to nano-NiO by earlier workers [19,21]. The appearance of PANI peaks centered between 2θ=20°-30° [24] indicates that the PANI stains have adsorbed on the surface of nickel oxide [21].

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Figure 2a: XRD spectra of PANI.

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Figure 2b: XRD spectra of NiO-PANI composite.

SEM analysis of NiO and NiO-PANI composite: The structural surface morphology of metal oxide and composite are given in FIG. 3a and 3b. It is noticed from the figures that the metal oxide looks like a uniform spherical ball and the composite appears like a cluster with increase in diameter. This matches very well with the earlier report [23].

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Figure 3: SEM spectra of (a) NiO and (b) NiO-PANI composite.

Preparation of electrode materials

The mild steel coupons having C: 0.21%, Si: 0.035%, Mn: 0.25%, P: 0.082% and 99.28% Fe, were cut in to pieces of dimension 4 cm × 2 cm × 0.2 cm, abraded with different grade abrasive papers starting from 600 to 1200 grit. The abraded coupons were washed with absolute ethanol, double distilled water, dried with acetone and kept in a desiccator. The inhibition efficiency was carried out with freshly polished coupons.

Preparation of electrolytic solutions.

The analytical grade sulphuric acid was diluted with distilled water to prepare the aggressive 1 M and 2 M sulphuric acid solutions. The test solutions were prepared by dissolving 100-500 ppm of composite in 1 M and 2 M sulphuric acid solutions.

Determination of inhibition property

Investigation on weight loss: The gravimetric method is the basic technique for inhibition assessment measurement. It was carried out at room temperature for eight hours continuously. Assessment on weight loss were discovered for the blank and different concentrated test solutions (250 ml) under total immersion of pre-weighed coupons. The specimens were taken out at two hours interval. Washed with bristle brush in absolute ethanol, distilled water and acetone and then dried at room temperature and reweighed. The inhibition efficiency (IE%) and surface coverage (θ) of composite were calculated using the formulae reported earlier [24].

Surface coverage area (θ)=(Wo-Wi/Wo)

Inhibition efficiency (IE %)=(Wo-Wi/Wo) × 100

Where Wo is the loss in weight for uninhibited and Wi is the loss in weight for test solutions. The calculated values are presented in (TABLES 1 and 2).

Conc. of composite (ppm) 2-hours 4-hours 6-hours 8-hours
Weight loss (g)  I.E (%) (θ) Weight loss (g) I.E (%) (θ) Weight loss (g)  I.E (%) (θ) Weight loss (g) I.E (%) (θ)
Blank 0.1351 -- -- 0.2275 -- -- 0.2982 -- -- 0.3666 -- --
125 0.0237 82 0.824 0.0401 82 0.819 0.0523 82 0.824 0.0680 81 0.814
250 0.0193 85 0.857 0.0332 85 0.854 0.0520 83 0.825 0.0676 82 0.816
375 0.0190 86 0.859 0.0321 86 0.858 0.0459 85 0.846 0.0624 83 0.829
500 0.0167 88 0.876 0.0290 87 0.872 0.0413 86 0.861 0.0580 84 0.841

Table 1: IE and θ values calculated from the weight loss measurement in 1 M blank and test solutions.

Conc. of composite (ppm) 2-hours 4-hours 6-hours 8-hours
Weight loss (g)  I.E (%) (θ) Weight loss (g) I.E (%) (θ) Weight loss (g)  I.E (%) (θ) Weight loss (g) I.E (%) (θ)
Blank 0.2412 -- -- 0.4172 -- -- 0.5507 -- -- 0.7046 -- --
125 0.0520 78 0.784 0.0950 77 0.772 0.1300 76 0.764 0.1750 75 0.175
250 0.0479 80 0.801 0.0856 79 0.794 0.1201 78 0.782 0.1550 78 0.780
375 0.0450 81 0.813 0.0848 80 0.797 0.1160 79 0.789 0.1490 79 0.788
500 0.0433 82 0.820 0.0804 81 0.802 0.1110 80 0.798 0.1377 80 0.803

Table 2: IE and θ values calculated from the weight loss measurement in 2 M blank and test solutions.

Careful analysis of the data presented in the (TABLES 1 and 2) reveals that the NiO-PANI composite is capable of giving protection against corrosion environment with slight variation in efficiency up to eight hours when its concentration is greater than 250 ppm.

Open circuit potential: Cell, having 1 cm2 area of mild steel as working electrode, platinum electrode as counter electrode and standard calomel electrode as reference electrode is used to measures the open circuit potential in CHI Electrochemical analyzer 1200B model. The OCP data were recorded for 1 M and 2 M solutions continuously upto 120 minutes and 180 minutes respectively. The results observed are presented in (FIG. 4 and 5).

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Figure 4: OCP plot for mild steel in 1 M H2SO4.

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Figure 5: OCP plot for mild steel in 2 M H2SO4.

For blank solution sharp fall in OCP values is noticed. By increasing the concentration of NiO-PANI composite the OCP values shifted to positive potential value and also only slight variation is recorded with increase in time. This observation is in good agreement with earlier reports [25,26].

Electrochemical measurements: A Potentiostat/Galvanostat EC-LAB Analyzer model 10.37 with three electrode cell assembly was used to measures electrochemical studies. ASTM 415 mild steel specimen of 1 cm2 area was used as working electrode. The remaining area of the working electrode was pasted with araldite epoxy resin. Platinum electrode was used as counter electrode and saturated calomel electrode was used as reference electrode in the cell assembly. Polarization studies were recorded from -200 to +200 mV with scan rate of 0.5 mV s-1. Frequency range of 100 kHz-10 mHz was adopted with amplitude of 10 mV AC sine wave for EIS studies.

Potentiodynamic polarization meassurements: The Tafel plot recorded for blank and test solutions with different amount of NiO-PANI composite are shown in (FIG. 6 and 7). The values of Icorr, Ecorr, bc and ba calculated from the Tafel plots are presented in the (TABLES 3 and 4) respectively. The efficiency of NiO-PANI composite to prevent corrosion is calculated by the formula reported elsewhere [27].

equation

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Figure 6: Potentiodynamic polarization curve of mild steel in 1 M blank and test solutions.

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Figure 7: Potentiodynamic polarization curve of mild steel in 2 M blank and test solutions.

Conc. of composite (ppm) -ECorr
(mV vs. SCE)
ba
(mV dec-1)
bc
(mV dec-1)
Icorr
(μA cm-2)
Inhibition Efficiency (%) Surface coverage (θ)
Blank 455 61 63 1960 -- --
100 495 27 36 1041 47 0.4688
200 477 35 37 517 74 0.7362
300 495 22 16 501 75 0.7456
400 471 22 44 456 77 0.7673
500 485 19 21 433 78 0.7790

Table 3: Corrosion Kinetic Parameters of Mild Steel in 1 M blank and test solution.

Conc. of composite (ppm) -ECorr
(mV vs. SCE)
ba (mV dec-1) bc (mV dec-1) Icorr (μA cm-2) Inhibition efficiency (%) Surface coverage (θ)
Blank 439 44 57 2537 -- --
100 495 41 51 1568 38 0.3819
200 473 22 23 1266 50 0.5009
300 471 15 16 962 62 0.6207
400 450 20 30 783 69 0.6913
500 465 15 17 675 73 0.7339

Table 4: Corrosion kinetic parameters of mild steel in 2 M H2SO4 with composite.

Data presented in (TABLES 3 and 4) exposes that corrosion current increases with increase in concentration of acid. Addition of inhibitor decreases the Icorr value irrespective of the acid strength. Steady decrease in the Icorr value reflects the protection efficiency of the composite. Minimal changes observed on Ecorr, ba and bc by varying concentration of inhibitor exposes it as mixed type inhibitor [28].

Electrochemical impedance measurements: Perfect semicircle appearance of Nyquist representation indicates the resistivity against corrosion and also reflect single charge transfer process [29]. The increase in size of loop with increase in concentration of composite in the (FIG. 8 and 9) discloses that the composite gets adsorbed over the metal surface and prevent the flow of corrosion current and thereby act as a good inhibitor in strong acidic environment. The relationship reported earlier [27] is used to calculate the IE values.

equation

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Figure 8: Impedance plot for mild steel in 1 M blank and test solution.

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Figure 9: Impendence plot for mild steel in 2 M blank and test solution.

The increase in Rct values display that the inhibitor forms a protective film at the electrolyte/metal interface [30]. Decrease in Cdl values exhibit that the electrical double layer thickness formed increases with the more addition of composite (TABLES 5 and 6).

Conc. of
composite (ppm)
Rs (Ω) Cdl (μ F cm-2) Rct (Ω cm2) Inhibition efficiency (%) Surface
Coverage (θ)
Blank 0.9997 542 0.7675 -- --
100 1.0490 552 1.051 27 0.2697
200 1.0940 501 1.226 37 0.3738
300 1.1540 552 1.275 40 0.2981
400 1.0450 383 2.901 73 0.7354
500 0.9898 320 3.846 80 0.8024

Table 5: . Impedance parameters for mild Steel in 1 M blank and test solution.

Conc. of
composite (ppm)
Rs (Ω) Cdl (μ F cm-2) Rct (Ω cm2) Inhibition efficiency (%) Surface
coverage (θ)
Blank 0.6058 850 0.4927 -- --
100 0.6994 887 0.5680 13 0.1325
200 0.6950 721 0.6015 18 0.1809
300 0.5549 594 1.0080 51 0.5112
400 0.6930 705 1.8660 75 0.7490
500 0.6479 538 2.040 76 0.7585

Table 6: Impedance parameters for mild steel in 2 M blank and test solution.

Conclusion

The universal solvent soluble, polymer coated metal oxide composite synthesized exhibit good protection efficiency upto 80% even in strong 2 M acidic condition and is also stable for more than three hours under corrosive environment. Similar increasing trend of protection efficiency with respect to the concentration of composite noticed in gravimetric method, OCP measurements and electrochemical studies implies that the water-soluble material can act as good safeguarding agent during industrial cleaning process.

Acknowledgement

The authors acknowledge the support from Dr. B.V., Dean for Research, SRM group of institutions, Dr. C. Jayaprabha, Associate Professor of Chemistry, University college of Engineering (Anna University) Dindigul-624622 and the Management of Rajalakshmi Engineering college, Chennai for the electrochemical analysis of samples on free of cost. This research did not receive any specific grant from funding agencies in the public, commercial or not for profit sectors.

References