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Materials Chemistry and Physics 122 (2010) 374–379

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

nhibition of mild steel corrosion in 1 M hydrochloric acid by-(N,N-dimethylaminobenzilidine)-3-mercapto-6-methyl-,2,4-triazin(4H)-5-one (DAMMT)

am John, Bincy Joseph, K.K. Aravindakshan, Abraham Joseph ∗

epartment of Chemistry, University of Calicut, Calicut – 673 635, Kerala, India

r t i c l e i n f o

rticle history:eceived 11 July 2009eceived in revised form 11 February 2010

a b s t r a c t

The corrosion behaviour of mild steel in 1 M HCl was studied using 4-(N,N-dimethylaminobenzilidine)-3-mercapto-6-methyl-1,2,4-triazin(4H)-5-one (DAMMT) as inhibitor using the conventional weight loss

ccepted 6 March 2010

eywords:orrosion inhibitionlectrochemical impedance spectroscopyydrochloric aciduantum chemical calculations

method, potentiodynamic polarisation studies(Tafel), linear polarisation studies (LPR), electrochemicalimpedance spectroscopy studies (EIS) adsorption studies and quantum chemical calculations. The effectof inhibitor concentrations, inhibition time, corrosion rate and surface coverage are investigated. Thecorrosion rate and other parameters evaluated for different inhibitor concentrations and the probablemechanism is proposed. The results showed that DAMMT posses excellent inhibition effect towards MSand the compound act as a mixed type inhibitor. The inhibitor molecules were first adsorbed on the MSsurface and blocking the reaction sites available for acid attack.

. Introduction

The use of inhibitors is one of the most practical methods forrotecting metals against corrosion and it is becoming increas-

ngly popular. In recent years, considerable efforts have beenade to develop environmentally benign and chemically efficient

orrosion inhibitors. Organic and inorganic molecules containingulphur and/or nitrogen have been found to be particularly effec-ive [1–5]. It is well known that a particular inhibitor that givesery high efficiency for a particular metal in a specific media mayot work with the same efficiency for other metals in the sameedia. Hackerman, Hurd, Anand and Aramaki [6–9] published a

eries of papers on polymethylene imines as inhibitors for steelorrosion in hydrochloric acid. These studies were extended tonclude polymeric amines, and the results showed that solubleolymeric molecules containing multiple repeating units identical

n functionality are more efficient corrosion inhibitors than the cor-esponding monomers. Riggs and Hurd reported the effectivenessf quaternary amines as adsorption inhibitors for steel corrosion in

ydrochloric acid. The strength of the adsorption depends mainlyn the electronic structure of the organic ligands [10–15]. Currently,he research is oriented to the development of ‘green corrosionnhibitors’ with good efficiency and low risk of environmental pol-ution [15–17].

∗ Corresponding author.E-mail address: drabrahamj@gmail.com (A. Joseph).

254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2010.03.008

© 2010 Elsevier B.V. All rights reserved.

The corrosion inhibition efficiency of organic molecules mainlydepends on their ability to get adsorb on the metal surface withthe replacement of water molecules at a corroding interface [18].The adsorption of organic molecules at the metal/solution inter-face is of great interest in surface science and can markedlychange the corrosion resisting properties of metals. The aimof the present work is to investigate the corrosion inhibitionefficiency of 4-(N,N-dimethylaminobenzilidine)-3-mercapto-6-methyl-1,2,4-triazin(4H)-5-one (DAMMT) towards mild steel in1 M hydrochloric acid.

2. Experimental

2.1. Inhibitor

The inhibitor, DAMMT is prepared by condensing 4-amino-3-mercapto-6-methyl-1,2,4-triazine-4H-5-one with N,N-dimethyamine benzaldehyde. The formercompound is synthesised in the laboratory by reacting pyruvic acid with thiocarbo-hydrazide procured from E.merk. The purified and recrystallised DAMMT sample ischaracterised by elemental analysis, FTIR and HNMR. The elemental analysis resultsshows the percentage of various elements in the compound are Cal (Expt.) C; 53.96(52.89), H; 5.23 (5.03), N; 24.2 (23.26), O; 5.23, S; 11.8 (10.73).

The probable assignments of FTIR (KBr) � (cm−1) 3194.5 (N–H), 3100.7 (Ar–H),2911.9 (C–H), 1704.7 (C O), 1592.9 (C N), 1540 (1515.7) (N–H), 1426.1 (–NCS),

1

1064.5 (N–N), 680 (Ar); and H NMR (DMSO-d6) (ppm) �: 7.5–7.6 (dd, J = 8.55 Hz,4H, Ar), 3.3–3.4 (S, J = 6.99 Hz, 6H, –N(CH3)2), 9 (S, 1H, N CH), 13.63 (S, 1H, –NH),2.08 (S, 1H, –CH3).

The compound is readily soluble in water at room temperature and its variousconcentrations were tested in the present study. The structure of the compound isgiven in Fig. 1.

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inhibitive efficiency is not very significant. The weight loss datawere used to calculate the corrosion rates and inhibition effi-ciencies. The variation of corrosion rate with exposure time atvarious inhibitor concentrations are given in Table 1 and the cor-rosion inhibition efficiency with different inhibitor concentrations

Table 1Corrosion rates of MS in 1 M HCl in the presence of DAMMT.

Conc. (ppm) Corrosion rate (mm/year) with time in hours

24 48 72 96

Blank 2112 1456 1008 777

Fig. 1. Structure of the inhibitor molecule (DAMMT).

.2. Medium

The medium for the study was prepared from reagent grade HCl from E.merknd doubly distilled water. All the tests were performed in aerated medium at roomemperature (27 ◦C) and normal atmospheric pressure.

.3. Materials

The materials were of the following composition (wt); C (0.20%), Mn (1%), P0.03%), S (0.02%), and Fe (98.75%). The mild steel specimens used in the weight loss

easurements were cut in to 4.8 × 1.9 cm2 coupons. The same types of coupons weresed for the electrochemical studies also. However, in electrochemical studies onlycm2 area is exposed. Before both the measurements, the samples were polishedsing different grade emery papers followed by washing in ethanol, acetone andnally with distilled water.

.4. Weight loss measurements

The weight loss experiments were carried out under total immersion conditionsn test solution maintained at 300 K. Mild steel specimens of required dimension isrst rubbed with different grade of emery papers to remove rust particles and thenubjected to the action of a buffing machine attached with a cotton wheel and abre wheel having buffing soap to ensure mirror bright finish. All specimens wereleaned according ASTM standard G-1-72 procedure [19–24]. The experiments werearried out in 250-ml beaker containing the solution. After the exposure periodhe specimens were removed, washed initially under running tap water, to removehe loosely adhering corrosion products and finally cleaned with a mixture of 20%aOH and 200 g/L zinc dust for 5 min followed by acetone. Similar experimentsere performed at the same temperature with different inhibitor concentrations tond out the most suitable inhibitor concentration that shows maximum inhibitivefficiency. From the weight loss in each experiment the corrosion rate was calculatedn mills per year (mpy). In each case duplicate experiments were conducted andhowed that the second results were within ±1% of the first. Whenever the variationsere very large, the data were confirmed by a third test. The inhibition efficiencyas taken to represent the surface coverage (�). The percentage inhibitive efficiencyas calculated using the relation:

E% = W0 − W

W0× 100 (1)

here W0 and W are the weight losses in the uninhibited and inhibited solution,espectively.

.5. Potentiodynamic polarisation studies

For the electrochemical measurements Gill AC Computer controlled electro-hemical workstation from ACM, UK (Model number: 1475) was used. A single wallne-compartment cell with a three-electrode configuration with a platinum sheet1 cm2 surface area) and SCE electrode were used as the auxiliary and the refer-nce electrodes respectively. The working electrode was first immersed in the testolution and after establishing a steady state open circuit potential, the electrochem-cal measurements were carried out. The polarisation curves were obtained in theotential ranges from −250 mV to +250 mV with a sweep rate of 1000 mV/min. Thelectrochemical parameters like corrosion potential (Ecorr), corrosion current den-

ity (Icorr), corrosion rate (CR) and inhibition efficiency (�%) values were calculatedrom these curves. The inhibition efficiency IE% was calculated from polarisation

easurements according to the relation:

= Icorr∗ − Icorr

Icorr∗× 100 (2)

d Physics 122 (2010) 374–379 375

where Icorr∗ and Icorr are uninhibited and inhibited corrosion current density, respec-tively.

2.6. Linear polarisation method

In order to determine the polarisation resistance, Rp, the potential of the workingelectrode was ramped ±10 mV in the vicinity of the corrosion potential at a scanrate of 1000 mV/min. Polarisation resistance were determined from the slope of thepotential versus current lines:

Rp = AdE

di

where A is the surface area of the electrode.The percentage inhibition efficiency is evaluated as follows:

IE% =R◦

p − Rp

R◦p

× 100

where Rp◦ and Rp are the polarisation resistance values in the absence and presence

of the inhibitor respectively.

2.7. Electrochemical Impedance Studies

Electrochemical tests were carried out in a conventional three-electrode con-figuration with platinum sheet (1 cm2 surface area) as auxiliary electrode andsaturated calomel electrode (SCE) as the reference electrode. The working electrodewas first immersed in the test solution and after establishing a steady state OCP,the electrochemical measurements were carried out in a Gill A C computer con-trolled electrochemical workstation (ACM, UK, model no: 1475). Electrochemicalimpedance spectroscopy (EIS) measurements were carried out in frequency rangeof 10 KHz to 10 Hz with amplitude of 10 Mv (RMS) using a.c. signals at open circuitpotential.

2.8. Quantum chemical calculations

Computational quantum chemical calculations were performed using ab ini-tio SCHF, 6-31G* basis set in order to investigate the charge distribution on DAMMTmolecule. The Mullicken charge distribution of DAMMT molecule as well as the high-est occupied molecular orbital (HOMO) and lowest unoccupied molecular orbitalLUMO) were calculated. In order to understand the adsorption phenomenon andthe adsorption energy, the Monte Carlo simulation studies have been made usingDAMMT molecule on Fe2O3 (1 1 1) surface.

2.9. Adsorption studies

It is generally assumed that the adsorption of the inhibitors on the metal surfaceis the essential step in the inhibition mechanism. To determine the adsorption mode,various isotherms were tested and the Langmuir should be the best, which give astraight-line graph for the plot of log�/1 – � vs. log C. Where � = Uo − Ui/Uo; Uo is theuninhibited corrosion rate, Ui is the inhibited corrosion rate, C is the concentrationof the inhibitor in moles/litre.

3. Results and discussion

3.1. Weight loss

The weight loss enhances with increasing exposure time anddecreases with increasing inhibitor concentration. If it increasesbeyond a particular concentration (threshold), the change in the

10 1025 616 457 39050 636 406 318 277100 391 300 250 225200 126 84 74 66400 104 69 61 56

376 S. John et al. / Materials Chemistry and Physics 122 (2010) 374–379

Table 2Percentage inhibition efficiency of DAMMT in 1 M HCl.

Conc. (ppm) % Inhibition efficiency with time in hours

24 48 72 96

Blank – – – –10 51.45 57.00 52.80 51.29

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50 69.85 72.13 68.44 65.37100 81.47 79.39 75.20 71.91200 94.01 94.18 92.68 92.26400 95.06 95.24 93.00 92.00

n mm/yr are given in Table 2. For a given exposure time theorrosion rate initially decreases considerably with inhibitor con-entration and reaches a minimum and later tends to stabilizer increase. The corrosion rate decreases and inhibition efficiencyncreases with increasing concentration of DAMMT. The corrosionnhibition efficiency however shows a reverse trend with exposureime.

.2. Polarisation studies

Polarisation curves for MS in 1 M HCl in the absence and pres-nce of DAMMT at room temperature are shown in Fig. 2. It islear from the figure that both the anodic metal dissolution andathodic hydrogen evolution reactions were inhibited after theddition of DAMMT to the aggressive medium. The inhibitions ofhese reactions are more pronounced with the increasing inhibitoroncentration while the corrosion potential values remained nearlyhe same. These results suggest that DAMMT acts as mixed type cor-osion inhibitor. The inhibitor molecules are first adsorbed on theS surface and blocking the available reaction sites [25]. The sur-

ace coverage increases with increase in inhibitor concentrations.he presence of defects on the metal surface permits free accesso H+ ions [26] and a significant dissolution of metal takes place,ollowed by desorption of the inhibitor film from the metal surface27]. The observed phenomenon is generally described as the cor-osion inhibition of the metal with the formation of a protectiveayer of adsorbed species at the metal surface [28,29]. It is clearrom these plots that both the anodic and cathodic current val-es were considerably increased in uninhibited 1 M HCl solutionshen compared with the inhibited solutions (Fig. 2). This observa-

ion can be explained with an increase in surface area of the metal

ue to the excess dissolution of iron. It is evident that the corrosionurrent density (Icorr) of the MS is much smaller when DAMMTs added to the aggressive solution. The change in the slope ofathodic current–potential line and anodic current–potential linendicates the modification of both anodic and cathodic reaction

ig. 2. Potentiodynamic polarisation curves for of MS in 1 M HCl in the absence andresence of different concentrations of DAMMT at 300 K.

Fig. 3. Equivalent circuit of constant phase element (CPE).

mechanisms in inhibited solution with time (Fig. 2). The forma-tion of the inhibitor film on the MS surface provides considerableprotection to the metal against corrosion. The corrosion currentdensity, inhibition efficiency and corrosion rate are given in Table 3.

3.3. Electrochemical impedance spectroscopy

The performance of the organic coatings on the metal can beevaluated from the EIS studies and this has been widely used forinvestigation of the protective properties of organic inhibitors onmetals. It does not disturb the double layer at the metal/solutioninterface [30,31]. Therefore, more reliable results can be obtainedfrom this technique (Equivalent circuitis is given in Fig. 3). TheNyquist plots and the Bode diagrams for the MS in uninhibited 1 MHCl those containing various inhibitor concentrations after 1 h ofimmersion are given in Fig. 4. It is clear from these figures that inuninhibited solution, Nyquist plot yields a slightly depressed semi-circles and only one time constant in Bode format. This indicatesthe corrosion of the MS in the absence of inhibitor and mainly con-trolled by a charge transfer process [28,29,32]. In the evaluation ofNyquist plots, the difference in real impedance at lower and higherfrequencies is commonly considered as a charge transfer resistance.The charge transfer resistance must be corresponding to the resis-tance between the metal and OHP (Outer Helmholtz Plane). Thecontribution of all resistances correspond to the metal/solutioninterface, i.e., charge transfer resistance (Rct), diffuse layer resis-tance (Rd), accumulation resistance (Ra), film resistance (Rf), etc.must be taken into account. Therefore, in this study, the differencein real impedance at lower and higher frequencies is considered asthe polarisation resistance (Rp) [28–33]. The addition of DAMMTto the aggressive solution leads to a change of the impedance dia-

high frequency part of the spectrum. As seen from Fig. 5, the Rp

values increased with the DAMMT concentration, which can beattributed to the formation of a protective layer at the metal surface

Fig. 4. Nyquist plots for MS in 1 M HCl in the absence and presence of differentconcentrations of DAMMT at 300 K.

S. John et al. / Materials Chemistry and Physics 122 (2010) 374–379 377

Table 3Electrochemical parameters for mild steel obtained from polarisation curves in 1 M HCl at 300 K.

Conc. (ppm) Ecorr (mV) LPR (� cm2) ˇa (mV dec−1) ˇc (mV dec−1) Icorr (�A cm−2) CR (mm year−1) � (%P)

Blank −502 9.8 172 204 4190 30.82 –10 −523 15.4 107 171 1869 9.24 55.3850 −523 15.4 96 160 1703 7.92 59.34100 −505 19.7 85 128 1128 2.51 73.00200 −503 31.8 78 88 568 0.60 86.44400 −486 53.7 68 55 227 0.13 94.56

Table 4AC impedance data of MS with DAMMT in 1 M HCl solutions at 300 K.

Conc. (ppm) Rct (� cm2) Cdl (�F cm−2) Icorr (�A cm−2) CR (mm year−1) � (%P)

Blank 8.0 24.56 3259 37.26 –10 21.82 81.50 1195 13.67 63.34

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nd this layer acts as a barrier for the mass and the charge transfers.he values of polarisation resistance and percentage inhibition effi-iency values determined from the EIS measurements are given inable 4. The inhibition efficiency was calculated using the equation:

E% = R◦ct − Rct

R◦ct

× 100 (3)

here Rct◦ and Rct are values of the charge transfer resistance

bserved in the absence and presence of DAMMT. In this case, theS corrosion takes place only on the free surface of the metal and/orithin the pores must diffusion of dissolved oxygen or chlorine

hrough the pores of the protective layer [33]. The values of botholarisation resistance and corrosion inhibition efficiency (IE%) cor-esponding to the EIS and the LPR after 1 h immersion is given inables 3 and 4. The IE% values obtained from the EIS are com-arable and run parallel with those obtained from the LPR andhe potentiodynamic polarisation measurements. It is clear that a

oderate decrease of the Rp value in blank solution was obtainedith the increased immersion time. However, the Rp value in the

nhibited solution increases up to 24 h, and then tends to decreaseTables 5 and 6).

.4. Linear polarisation studies

Polarisation resistance values were obtained from the slope ofhe polarisation curves in the potential range ±10 mV with respecto the corrosion potential at a sweep rate of 1000 mV/min. Straight

ig. 5. Bode curves for mild steel in 1 M HCl in the presence of different concentra-ions of DAMMT at 300 K.

1069 12.23 67.21280 3.21 91.45104 1.20 96.78

43 0.50 98.65

lines were obtained in the potential range. In general, Rp valuesincreased with increasing inhibitor concentration as seen in Fig. 6.The rest potential values were used to calculate the inhibition effi-ciency. The parallel increase in the corrosion inhibition efficiencyfor MS in 1 M HCl with increasing inhibitor concentration can beexplained because of inhibitor adsorption. In blank solution, theEcorr values of the MS shifts towards more positive potentials con-tinuously up to 24 h and then stabilises around −0.490 mV. Theaddition of 100 ppm of DAMMT to 1 M HCl solution produce aconsiderable noble Ecorr value and tends to possess more cathodicvalues with increasing immersion time (Figs. 7 and 8). After 24 h,more negative Ecorr values were obtained in the inhibited solutionsand then tend to shift towards cathodic potential up to 96 h. Theresults clearly show the adsorption of DAMMT molecules on themetal surface.

3.5. Adsorption studies

Adsorption plays a significant role in the inhibition of metal-lic corrosion by organic molecules. Many investigators have usedLangmuir’ adsorption isotherm to study inhibitor characteris-tics assuming that the inhibitors adsorbed on the metal surface

decrease the surface area available for electrode reactions to takeplace [34–38]. According to Hoar and Holliday, the Langmuirisotherm should give a straight-line graph for the plot of log�/1 – �vs. log C. Where � = Uo − Ui/Uo; Uo is the uninhibited corrosion rate,Ui is the inhibited corrosion rate, C is the concentration of the

Fig. 6. Linear polarisation curves for mild steel in 1 M HCl in the absence and pres-ence of different concentrations of DAMMT at 300 K.

378 S. John et al. / Materials Chemistry and Physics 122 (2010) 374–379

Table 5AC impedance data of mild steel with 100 ppm of DAMMT at different exposure time.

Time in hours Rct (� cm2) Cdl (�F cm−2) Icorr (�A cm−2) CR (mm year−1) � (%P)

0 60.80 74.02 429 4.91 –2 205.71 51.05 126 1.45 70.44

24 440.90 65.40 59 0.68 86.21

Table 6Electrochemical parameters for MS in 1 M HCl with 100 ppm of DAMMT at different exposure period.

Time in hours Ecorr (mV) LPR (� cm2) ˇa (mV dec−1) ˇc (mV dec−1) Icorr (�A cm−2) CR (mm year−1) � (%P)

0 −521 43.2 622 −509 138.1 54

24 −494 261.2 40

FD

i(daoiOosibp

Fa

simulation for adsorption of DAMMT molecule adsorbed on Fe(1 1 1) plane are presented in Table 7 and the simulated adsorption

ig. 7. Nyquist plots for MS in 1 M HCl in the absence and presence of 100 ppmAMMT at different immersion times at 300 K.

nhibitor in moles/litre. The plots at the experimental temperature300 K) corresponding to mild steel is a straight line, but the gra-ients are not equal to unity as is expected for the ideal Langmuirdsorption isotherm (Fig. 9). This may be due to the interactionf adsorbed molecules on the metal surface, which is completelygnored during the derivation of Langmuir equation (R2 = 0.9898).rganic molecules having polar atoms or groups being adsorbedn the metal surface may interact by mutual attraction or repul-ion. These interactions would affect the heat of adsorption of the

nhibitors. If the interaction is repulsive, the heat of adsorption wille negative and if it is attractive, the heat of adsorption will beositive. The cathodic hydrogen evolution reaction may be given

ig. 8. Linear polarisation curves for mild steel in 1 M HCl in the presence of DAMMTt different immersion times at 300 K.

97 382 2.42 –66 94 0.55 75.2744 35 0.17 90.07

as follow:

Fe + H+ ↔ [FeH+]ads

[FeH+]ads + e− → [FeH]ads

[FeH]ads + H+ + e− → Fe + H2

The protonated DAMTT molecule are adsorbed at cathodic sitesin competition with hydrogen ions that going to reduce H2 gasevolution [37].

3.6. Quantum chemical calculations

Molecular modelling studies give clear indication of strongmolecular attraction between the metal and DAMMT molecule.In Monte Carlo simulation, DAMMT molecule is placed on theFe2O3 (1 1 1) surface and performed molecular dynamics studies.The adsorption energy; the sum of the rigid adsorption energy anddeformation energy for the adsorbate components have been cal-culated. The rigid adsorption energy reports the energy released inkcal mol−1, when the unrelaxed adsorbate components adsorbedon the substrate. The deformation energy reports the energyreleased when the adsorbed adsorbate components are relaxedon the substrate surface. The total energy, rigid adsorption energydeformation energy, and dEad/dNi calculated by the Monte Carlo

diagram is given in Fig. 10 [39,40].The inhibition efficiency of a molecule depends on the energy

gap between the HOMO and LUMO levels. A good inhibitor

Fig. 9. Langmuir adsorption isotherm for mild steel in 1 M HCl 300 K in the presenceof DAMMT.

S. John et al. / Materials Chemistry and Physics 122 (2010) 374–379 379

Table 7Various quantum chemical parameters calculated by computational/simulation studies.

Adsorption parameters Quantum chemical parameters

Total energy (kcal mol−1) −405.0940 Total energy (kcal mol−1) 781,608.82Adsorption energy (kcal mol−1) −77.4862Rigid adsorption energy (kcal mol−1) −323.4404Deformation energy (kcal mol−1) −77.1629dEad/dNi (kcal mol−1) −77.4862

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[37] R. Solmaz, G. Kardas, M. Culha, B. Yazici, M. Erbil, Electrochim. Acta 53 (2008)

Fig. 10. Model of adsorption of DAMMT on Fe2O3 surface (1 1 1).

olecule offers electrons to the unoccupied orbital of metal butlso accept free electrons from metal. That is a charge transferhenomenon may takes place. In order to investigate the chargeistribution on DAMMT molecule ab initio quantum chemicalalculations were performed using SCHF, 6-31G* basis set. Theullicken charge distribution of DAMMT molecule as well as the

ighest occupied molecular orbital (HOMO) and lowest unoccupiedolecular orbital LUMO) were calculated. The charge distribution

f DAMMT molecule ranges from −0.820 to +0.820. The dipoleoment of the molecule is calculated to be 3.6292 D. From quan-

um chemical calculation it is clear that higher the HOMO energy ofhe inhibitor, greater is the trend of donating electrons to the unoc-upied ‘d’ orbital of the metal, and higher the corrosion inhibitionfficiency. The lower the LUMO energy level makes easy accep-ance of electrons from the metal surface. The magnitude of �Ealue (�E = ELUMO − EHOMO) also helps to predict probable roots ofhe inhibitory action. In DAMMT molecule the �E value approxi-

ately 10 eV. Smaller the �E value greater is the inhibitory action.he total energy, EHOMO and ELUMO are also presented in Table 7.

. Conclusion

The corrosion of mild steel in 1 M Hydrochloric acid can be inhib-ted by the use of DAMMT. DAMMT showed a very high inhibitivefficiency for mild steel in 1 M hydrochloric acid. Its percentagenhibitive efficiency increases with increase in concentration andecreases with longer exposure periods at 300 K. A higher coveragef the inhibitor on the metal surface was obtained in solutions withhe higher inhibitor concentrations.

Results of polarisation studies suggest that the inhibitor,AMMT, acts as mixed type inhibitor. The inhibitor molecules

dsorb on the MS surface and blocking the reaction sites. The sur-ace area available for the attack of the corrosive species decreasesith increasing inhibitor concentrations. Quantum chemical calcu-

ations show that the inhibitor molecule is having �E value in therder of 10 eV which confirms the insulating property of DAMMT

[[

[

EHOMO (eV) −8.0274ELUMO (eV) 2.2041�E (eV) 10.2315Dipole moment (D) 3.6292

molecule. Molecular simulation studies suggest the probable rootsthrough which the inhibitor molecules adsorb on the MS surface.

Acknowledgements

The authors are very much grateful to Kerala State Council forScience Technology and Environment (KSCSTE) for financial sup-port in the form of a major research project 018/SRSPS/2006/CSTE.

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