Research Article The Inhibition Effect of Potassium...
Transcript of Research Article The Inhibition Effect of Potassium...
Research ArticleThe Inhibition Effect of Potassium Iodide on the Corrosion ofPure Iron in Sulphuric Acid
Tarik Attar12 Lahcegravene Larabi1 and Yahia Harek1
1 Laboratory of Analytical Chemistry and Electrochemistry Department of Chemistry Faculty of Sciences PO Box 119University Abou-Bekr Belkaıd 13000 Tlemcen Algeria
2 University Center of Naama BP 66 45000 Naama Algeria
Correspondence should be addressed to Tarik Attar t attarmailuniv-tlemcendz
Received 29 June 2014 Accepted 8 September 2014 Published 24 September 2014
Academic Editor Armando Zarrelli
Copyright copy 2014 Tarik Attar et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The use of inorganic inhibitors as an alternative to organic compounds is based on the possibility of degradation of organiccompounds with time and temperature The inhibition effect of potassium iodide on the corrosion of pure iron in 05M H
2SO4
has been studied by weight loss It has been observed from the results that the inhibition efficiency (IE) of KI increases from8217 to 9751 with the increase in inhibitor concentration from 1sdot10minus4 to 2sdot10minus3MThe apparent activation energy (119864
119886) and the
equilibrium constant of adsorption (119870ads) were calculated The adsorption of the inhibitor on the pure iron surface is in agreementwith Langmuir adsorption isotherm
1 Introduction
Corrosion is the deterioration of materials by chemical inter-action with their environment [1] Corrosion can cause disas-trous damage to metal and alloy structures causing economicconsequences in terms of repair replacement product lossessafety and environmental pollution [2] Several protectivemeasures are taken to control and prevent corrosion Oneof these is the use of corrosion inhibitors which are usuallychemical substances when added in a small concentration toa corrosive medium they reduce effectively the corrosion ofthe metal andor alloy [3 4] The use of corrosion inhibitorsconstitutes one of the most economical ways to mitigate thecorrosion rate [5] The corrosion and corrosion protection ofiron in corrosive environments have attracted the attentionof many investigators [6ndash8] Iron plays a central role as oneof the most widely used materials in our daily life becauseof its so many applications [9] The inhibition efficiencydepends on the parameters of the corrosive system [pHtemperature duration metal composition etc] and on thenature of the inhibitor [10] Sulfuric acid is one of the mostaggressive acids for iron and its alloys and is often used duringcleaning pickling descaling acidizing and so forth [11 12]The inhibitor molecules get bonded to the metal surface
by chemisorption physisorption or complexation with thepolar groups acting as the reactive centers in the molecules[13]
2 Experimental
21 Materials The weight loss experiments were conductedin a 150mL beaker the electrolyte volume is 100mL Julabothermostat brand keeps the electrolyte at the desired temper-ature (plusmn01∘C)
The test pieces were mechanically polished with emerypaper (a coarse paper was used initially and then progres-sively finer grades were employed 400 to 1200 grade) Thespecimens were weighed by electronic digital analytical bal-ance with five decimal accuracies before and after exposure
22 Electrolyte The corrosive solution 05M H2SO4 was
obtained by dilution of analytical grade 98 sulphuric acidwith bidistilled water The concentration range of inhibitoremployed was 1sdot10minus4 to 2sdot10minus3M in the sulphuric acid
23 Weight Loss Method The test pieces were washed withbidistilled water degreased with acetone washed again
Hindawi Publishing CorporationAdvances in ChemistryVolume 2014 Article ID 827514 5 pageshttpdxdoiorg1011552014827514
2 Advances in Chemistry
with bidistilled water dried between two filter papers andweighed After specified periods of time 3 test pieces weretaken out of the test solution rinsed with bidistilled waterdried as before and weighed again The average weight lossat a certain time for each set of three samples was taken Theweight loss experiments were performed after an exposureof 2 h The inhibition efficiency of potassium iodide wasexpressed in terms of percentage inhibition calculated using
IE () = (119908corr minus 119908inh119908corr
) times 100 (1)
where 119882corr is the corrosion rate of blank sulfuric acid and119882inh is the corrosion rate after adding inhibitor
The corrosion rate (119882) was calculated from the followingequation
119908 = (
119898
1minus 119898
2
119878 sdot 119905
) (2)
where1198981is the mass of the specimen before corrosion119898
2is
the mass of the specimen after corrosion 119878 is the total area ofthe specimen 119905 is the corrosion time and119882 is the corrosionrate
The degree of surface coverage (Θ) was calculated usingthe following equation
120579 = 1 minus
119908inh119908corr (3)
3 Results and Discussion
31 Effect of Inhibitor Concentration Thevalues of percentageinhibition efficiency (IE) and corrosion rate (w) at differentconcentrations of KI at 303K are summarized in Table 1Figure 1 shows the results obtained fromweight lossmeasure-ments for pure iron in 05M H
2SO4solutions in the absence
and presence of different concentrations of KI It has beenobserved from the results that the IE of KI increases from8217 to 9751 with the increase in inhibitor concentrationfrom 1sdot10minus4 to 2sdot10minus3M The optimum concentration of thiseffect is 2sdot10minus3M
Figure 2 shows that the corrosion rate decreases withincreasing concentration of inhibitor which explains theeffect of protection against the corrosion by the type ofinhibitor selected
32 Effect of Immersion Time Theweight loss measurementswere performed in 05M H
2SO4in absence and presence of
KI at 2sdot10minus3M concentration for 30min to 6 h immersiontime at temperature of 303K Inhibition efficiencies wereplotted against immersion time as seen in Figure 3This figureshows that inhibition efficiency of the potassium iodide wasincreased with increasing immersion time The increase ininhibition efficiency up to 2 h reflects the inorganic inhibitoradsorption of constituents on the pure iron surface Thisresult indicates a stabilization of the inhibition rate from 2hours of immersion According to this study it was found thatKI is a very effective inhibitor for pure iron in H
2SO405M
because after an immersion time of half an hour the power ofprotection already achieved 9491
975
900
825
00 50 times 10minus4
10 times 10minus3
15 times 10minus3
20 times 10minus3
IE (
)
C (molL)
Figure 1 Variation of inhibition efficiency with KI concentration
00 05 10 15 20
030
025
020
015
010
005
C (molL)
w(m
gcm
2middoth)
times10minus3
Figure 2 Plot of corrosion rate versus inhibitor concentration forpure iron test specimens after 2 hrs of exposure
33 Effect of Temperature In order to study the effect of tem-perature on the inhibition efficiencies of potassium iodideweight loss measurements were carried out in the tempera-ture range 293ndash323K in absence and presence of inhibitor atoptimumconcentration during 2 hours of immersion Table 2shows the effect of temperature on the corrosion rate of pureiron in absence and presence of inhibitor It is evident fromthis table that inhibition efficiency increases with increasingtemperature
The apparent activation energy Ea for pure iron corrosionin 05MH
2SO4in the absence and presence of inhibitors was
evaluated from Arrhenius equation [14]
ln (119908) = minus119864
119886
119877119879
+ 119860 (4)
where 119908 is the corrosion rate determined from gravimetricmeasurements 119860 is the Arrhenius frequency factor 119877 is themolar gas constant and 119879 is the absolute temperature
The plots of ln(119908) against 1119879 were linear as shown in(Figure 4) 119864
119886values were obtained from the slope and are as
presented in Table 3
Advances in Chemistry 3
Table 1 Corrosion parameters for pure iron in aqueous solution of05MH2SO4 in presence and absence of different concentrations ofKI at 303K for 2 h
119862 (molL) 119908 (mgsdotcmminus2sdothminus1) IE ()H2SO4 05 160383 mdash
KI
1 sdot 10
minus4 028593 821725 sdot 10
minus4 010956 93165 sdot 10
minus4 007787 951575 sdot 10
minus4 005445 96601 sdot 10
minus3 004169 97112 sdot 10
minus3 003986 9751
Table 2 Effect of temperature on pure iron in the presence andabsence of KI at 2 h
119879 (K) 119908
0(mgcm2
sdoth1) 119908inh (mgcm2sdoth1) IE ()
293 015107 000622 9588303 034152 001329 9610313 132256 005035 9619323 343109 011280 9671
Table 3 The values of activation parameters for pure iron in05MH2SO4 in the absence and the presence of inhibitor of 2sdot10
minus3Mconcentration at 2 h
Concentrationof inhibitor (M)
119864
119886
(kJmol)Δ119867
119886
(kJmol)119864
119886minus Δ119867
119886
(kJmol)05H2SO4 8432 8165 2672 sdot 10
minus3 KI 7889 7622 267
Aplot of ln(119908119879) versus 1119879 gave a straight line (Figure 5)with a slope of minus(Δ119867
119886119877) from which the value of Δ119867
119886was
calculated and listed in Table 3The 119864
119886values in the presence of inhibitor are lower than
in the absence of inhibitor indicating that the inhibition effi-ciency increases with increases in temperature The positivesign of enthalpy of activation reflects the endothermic natureof the steel dissolution process
34 Adsorption Isotherm Adsorption isotherms provideinformation about the interaction of the adsorbed moleculeswith the electrode surface [15] The adsorption of theinhibitors can be described by two main types of interactionphysical adsorption and chemisorptions [16 17] These areinfluenced by the chemical structure of the inhibitor the typeof the electrolyte pH the charge and nature of the metal andtemperature [18] The phenomenon of interaction betweenthe metal surface and the inhibitor can be better understoodin terms of adsorption isothermThe plots of119862inh120579 against119862(Figure 6) yield a straight line with approximately unit slopeindicating that the inhibitor under study obeys Langmuiradsorption isotherm According to this isotherm 120579 is relatedto 119862inh by [19]
119862inh120579
=
1
119870ads+ 119862inh (5)
0 1 2 3 4 5 6
980
975
790
965
960
955
950
945
IE (
)
Time (h)
Figure 3 Variation of inhibition efficiency of KI with immersiontime
15
00
minus15
minus30
minus45
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
)(m
gcm
2middoth)
Figure 4 Adsorption isotherm plots for ln 119908 versus 1119879
minus45
minus60
minus75
minus90
minus105
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
T)(m
gcm
2middothmiddotK)
Figure 5 Adsorption isotherm plots for ln(119908119879) versus 1119879
4 Advances in Chemistry
20
15
10
05
00 05 10 15 20
Cinh (molL) times10minus3
times10minus3
Cin
h120579
(mol
L)
Figure 6 Relationship between (119862inh120579) and inhibitor concentra-tion 119862inh
The119870ads values can be calculated from the intercept lineson the 119862inh120579-axis This is related to the standard free energyof adsorption (Δ119866ads) with the following equation [20]
119870ads = (1
555
) exp(minusΔ119866ads119877119879
) (6)
where
Δ119866ads = minus119877119879 ln (555119870ads) (7)
where119877 is the gas constant and119879 is the absolute temperatureThe constant value of 555 is the concentration of water insolution in moldm3 [21]
The intercept permits the calculation of the equilib-rium constant 119870ads which is 617 times 104 Lmol respectivelyThe value of 119870ads which indicates the binding power ofthe inhibitor to the pure iron surface leads to calcula-tion of adsorption energy Value of Δ119866ads is minus3755 kJmolrespectively The negative values of Δ119866ads showed that theadsorption of inhibitor molecules on the metal surface isspontaneous [22]
Generally the standard free energy values of minus20 kJmolor less negative are associated with an electrostatic interac-tion between charged molecules and charged metal surface(physical adsorption) those of minus40 kJmol or more nega-tive involves charge sharing or transfer from the inhibitormolecules to the metal surface to form a co-ordinate covalentbond (chemical adsorption)
Note that our measures were carried out without inertatmosphere In 1M H+ the iodide ion becomes hydrogeniodide which reacts with oxygen to form molecule iodideI2 The formed molecule could be adsorbed onto iron and
occupying the surface it strikes the adsorption of iodideAt the end a lower efficiency of adsorption of iodide wasobtained but the inhibition efficiency of the studied inhibitorKI increases due to adsorption of I
2
Otherwise the value of Δ119866ads (minus3755 kJmol) near tominus40 kJmol indicates that in our case the adsorption isneither typical chemisorption nor typical physisorption but
it is a complex mixed type That is the adsorption inhibitormolecule on the iron surface in the present study involvesboth chemisorption (of I
2) and physisorption (of Iminus) but
chemisorption is the predominant mode of adsorptionThis assumption is supported by the data obtained fromtemperature dependence of inhibition process reported inTables 2 and 3 which show that the inhibition efficiency ofthe studied compound as inhibitor increases with increasein temperature and that the value of 119864
119886in absence of the
inhibitor is lower than that in its presence [23] On the otherhand it is known that the iron surface acquires positive chargein H2SO405M [24] while iodide ion is negatively charged
as a result the physisorption (electrostatic attraction) of theiodide ion occurs onto iron surface
4 Conclusion
On the basis of the experimental results obtained in thepresent study the following conclusions can be drawn
(1) Potassium iodide is a good inhibitor for pure ironcorrosion in 05M H
2SO4solution The inhibition
efficiency increases with increased KI concentrationto attain a maximum value of 9751 at 2sdot10minus3M
(2) The adsorption of KI on pure iron obeyed Langmuiradsorption isotherm
(3) At higher experimental temperature inhibitormolecules are adsorbed into the metal surface
(4) The negative value of Δ119866ads is a sign of spontaneousadsorption on the metal surface
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] B Eker and E Yuksel ldquoSolutions to corrosion caused byagricultural chemicalsrdquo Trakia Journal of Sciences vol 3 no 7pp 1ndash6 2005
[2] N Patni S Agarwal and P Shah ldquoGreener Approach towardsCorrosion Inhibitionrdquo Chinese Journal of Engineering vol 2013Article ID 784186 10 pages 2013
[3] T H Ibrahim and M A Zour ldquoCorrosion inhibition of mildsteel using fig leaves extract in hydrochloric acid solutionrdquoInternational Journal of Electrochemical Science vol 6 no 12pp 6442ndash6455 2011
[4] E-S M Sherif ldquoElectrochemical and gravimetric study on thecorrosion and corrosion inhibition of pure copper in sodiumchloride solutions by two azole derivativesrdquo International Jour-nal of Electrochemical Science vol 7 no 2 pp 1482ndash1495 2012
[5] P Rajeev A O Surendranathan and C S N Murthy ldquoCorro-sion mitigation of the oil well steels using organic inhibitorsmdashareviewrdquo Journal of Materials and Environmental Science vol 3no 5 pp 856ndash869 2012
Advances in Chemistry 5
[6] E-S M Sherif ldquoCorrosion and corrosion inhibitionof pure iron in neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquo International Journal ofElectrochemical Science vol 6 no 8 pp 3077ndash3092 2011
[7] H Amar A Tounsi A Makayssi A Derja J Benzakour andA Outzourhit ldquoCorrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3 mediardquo Corro-sion Science vol 49 no 7 pp 2936ndash2945 2007
[8] E-SM Sherif RM Erasmus and JD Comins ldquoIn situ Ramanspectroscopy and electrochemical techniques for studying cor-rosion and corrosion inhibition of iron in sodium chloridesolutionsrdquo Electrochimica Acta vol 55 no 11 pp 3657ndash36632010
[9] E SM Sherif ldquoCorrosion and corrosion inhibition of pure ironin neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquoInternational Journal of Electrochemical Science vol 6 pp 3077ndash3092 2011
[10] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012
[11] T Poornima N Jagannatha and A Nityananda Shetty ldquoStudieson corrosion of annealed and aged 18 Ni 250 grade maragingsteel in sulphuric acid mediumrdquo Portugaliae ElectrochimicaActa vol 28 no 3 pp 173ndash188 2010
[12] P Kumar and A N Shetty ldquoElectrochemical investigation onthe corrosion of 18Ni M250 grade maraging steel underwelded condition in sulfuric acid mediumrdquo Surface Engineeringand Applied Electrochemistry vol 49 no 3 pp 253ndash260 2013
[13] I Lukovits E Kalman and F Zucchi ldquoCorrosion inhibitorsmdashcorrelation between electronic structure and efficiencyrdquo Corro-sion vol 57 no 1 pp 3ndash8 2001
[14] M A Quraishi and S Khan ldquoThiadiazoles-A potential class ofheterocyclic inhibitors for prevention of mild steel corrosionin hydrochloric acid solutionrdquo Indian Journal of ChemicalTechnology vol 12 no 5 pp 576ndash581 2005
[15] E A Noor and A H Al-Moubaraki ldquoThermodynamicstudy of metal corrosion and inhibitor adsorptionprocesses in mild steel1-methyl-4[41015840(-X)-styryl pyridiniumiodideshydrochloric acid systemsrdquo Materials Chemistry andPhysics vol 110 no 1 pp 145ndash154 2008
[16] L Larabi O Benali and Y Harek ldquoCorrosion inhibition ofcopper in 1 M HNO
3solution by N-phenyl oxalic dihydrazide
and oxalic N-phenylhydrazide 1198731015840-phenylthiosemicarbaziderdquoPortugaliae Electrochimica Acta vol 24 no 3 pp 337ndash3462006
[17] L Larabi Y Harek M Traisnel and A Mansri ldquoSynergisticinfluence of poly(4-vinylpyridine) and potassium iodide oninhibition of corrosion of mild steel in 1M HClrdquo Journal ofApplied Electrochemistry vol 34 no 8 pp 833ndash839 2004
[18] M A Ameer and A M Fekry ldquoInhibition effect of newlysynthesized heterocyclic organicmolecules on corrosion of steelin alkaline medium containing chloriderdquo International Journalof Hydrogen Energy vol 35 no 20 pp 11387ndash11396 2010
[19] M Benabdellah A Aouniti A Dafali et al ldquoInvestigation ofthe inhibitive effect of triphenyltin 2-thiophene carboxylate oncorrosion of steel in 2 M H
3PO4solutionsrdquo Applied Surface
Science vol 252 no 23 pp 8341ndash8347 2006[20] A M Fekry and M A Ameer ldquoCorrosion inhibition of mild
steel in acidic media using newly synthesized heterocyclicorganic moleculesrdquo International Journal of Hydrogen Energyvol 35 no 14 pp 7641ndash7651 2010
[21] O Olivares N V Likhanova B Gomez et al ldquoElectrochemicaland XPS studies of decylamides of 120572-amino acids adsorptionon carbon steel in acidic environmentrdquo Applied Surface Sciencevol 252 no 8 pp 2894ndash2909 2006
[22] A Dabrowski ldquoAdsorption-from theory to practicerdquo Advancesin Colloid and Interface Science vol 93 no 1ndash3 pp 135ndash2242001
[23] T Szauer and A Brandt ldquoOn the role of fatty acid in adsorptionand corrosion inhibition of iron by amine-fatty acid salts inacidic solutionrdquo Electrochimica Acta vol 26 no 9 pp 1257ndash1260 1981
[24] B S Prathibha P Kottees waram and R V Bheema ldquoStudyon the inhibition of mild steel corrosion by quaterwareyAmmonium compound in H
2SO4mediumrdquo Research Journal of
Recent Sciences vol 2 no 4 pp 1ndash10 2013
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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2 Advances in Chemistry
with bidistilled water dried between two filter papers andweighed After specified periods of time 3 test pieces weretaken out of the test solution rinsed with bidistilled waterdried as before and weighed again The average weight lossat a certain time for each set of three samples was taken Theweight loss experiments were performed after an exposureof 2 h The inhibition efficiency of potassium iodide wasexpressed in terms of percentage inhibition calculated using
IE () = (119908corr minus 119908inh119908corr
) times 100 (1)
where 119882corr is the corrosion rate of blank sulfuric acid and119882inh is the corrosion rate after adding inhibitor
The corrosion rate (119882) was calculated from the followingequation
119908 = (
119898
1minus 119898
2
119878 sdot 119905
) (2)
where1198981is the mass of the specimen before corrosion119898
2is
the mass of the specimen after corrosion 119878 is the total area ofthe specimen 119905 is the corrosion time and119882 is the corrosionrate
The degree of surface coverage (Θ) was calculated usingthe following equation
120579 = 1 minus
119908inh119908corr (3)
3 Results and Discussion
31 Effect of Inhibitor Concentration Thevalues of percentageinhibition efficiency (IE) and corrosion rate (w) at differentconcentrations of KI at 303K are summarized in Table 1Figure 1 shows the results obtained fromweight lossmeasure-ments for pure iron in 05M H
2SO4solutions in the absence
and presence of different concentrations of KI It has beenobserved from the results that the IE of KI increases from8217 to 9751 with the increase in inhibitor concentrationfrom 1sdot10minus4 to 2sdot10minus3M The optimum concentration of thiseffect is 2sdot10minus3M
Figure 2 shows that the corrosion rate decreases withincreasing concentration of inhibitor which explains theeffect of protection against the corrosion by the type ofinhibitor selected
32 Effect of Immersion Time Theweight loss measurementswere performed in 05M H
2SO4in absence and presence of
KI at 2sdot10minus3M concentration for 30min to 6 h immersiontime at temperature of 303K Inhibition efficiencies wereplotted against immersion time as seen in Figure 3This figureshows that inhibition efficiency of the potassium iodide wasincreased with increasing immersion time The increase ininhibition efficiency up to 2 h reflects the inorganic inhibitoradsorption of constituents on the pure iron surface Thisresult indicates a stabilization of the inhibition rate from 2hours of immersion According to this study it was found thatKI is a very effective inhibitor for pure iron in H
2SO405M
because after an immersion time of half an hour the power ofprotection already achieved 9491
975
900
825
00 50 times 10minus4
10 times 10minus3
15 times 10minus3
20 times 10minus3
IE (
)
C (molL)
Figure 1 Variation of inhibition efficiency with KI concentration
00 05 10 15 20
030
025
020
015
010
005
C (molL)
w(m
gcm
2middoth)
times10minus3
Figure 2 Plot of corrosion rate versus inhibitor concentration forpure iron test specimens after 2 hrs of exposure
33 Effect of Temperature In order to study the effect of tem-perature on the inhibition efficiencies of potassium iodideweight loss measurements were carried out in the tempera-ture range 293ndash323K in absence and presence of inhibitor atoptimumconcentration during 2 hours of immersion Table 2shows the effect of temperature on the corrosion rate of pureiron in absence and presence of inhibitor It is evident fromthis table that inhibition efficiency increases with increasingtemperature
The apparent activation energy Ea for pure iron corrosionin 05MH
2SO4in the absence and presence of inhibitors was
evaluated from Arrhenius equation [14]
ln (119908) = minus119864
119886
119877119879
+ 119860 (4)
where 119908 is the corrosion rate determined from gravimetricmeasurements 119860 is the Arrhenius frequency factor 119877 is themolar gas constant and 119879 is the absolute temperature
The plots of ln(119908) against 1119879 were linear as shown in(Figure 4) 119864
119886values were obtained from the slope and are as
presented in Table 3
Advances in Chemistry 3
Table 1 Corrosion parameters for pure iron in aqueous solution of05MH2SO4 in presence and absence of different concentrations ofKI at 303K for 2 h
119862 (molL) 119908 (mgsdotcmminus2sdothminus1) IE ()H2SO4 05 160383 mdash
KI
1 sdot 10
minus4 028593 821725 sdot 10
minus4 010956 93165 sdot 10
minus4 007787 951575 sdot 10
minus4 005445 96601 sdot 10
minus3 004169 97112 sdot 10
minus3 003986 9751
Table 2 Effect of temperature on pure iron in the presence andabsence of KI at 2 h
119879 (K) 119908
0(mgcm2
sdoth1) 119908inh (mgcm2sdoth1) IE ()
293 015107 000622 9588303 034152 001329 9610313 132256 005035 9619323 343109 011280 9671
Table 3 The values of activation parameters for pure iron in05MH2SO4 in the absence and the presence of inhibitor of 2sdot10
minus3Mconcentration at 2 h
Concentrationof inhibitor (M)
119864
119886
(kJmol)Δ119867
119886
(kJmol)119864
119886minus Δ119867
119886
(kJmol)05H2SO4 8432 8165 2672 sdot 10
minus3 KI 7889 7622 267
Aplot of ln(119908119879) versus 1119879 gave a straight line (Figure 5)with a slope of minus(Δ119867
119886119877) from which the value of Δ119867
119886was
calculated and listed in Table 3The 119864
119886values in the presence of inhibitor are lower than
in the absence of inhibitor indicating that the inhibition effi-ciency increases with increases in temperature The positivesign of enthalpy of activation reflects the endothermic natureof the steel dissolution process
34 Adsorption Isotherm Adsorption isotherms provideinformation about the interaction of the adsorbed moleculeswith the electrode surface [15] The adsorption of theinhibitors can be described by two main types of interactionphysical adsorption and chemisorptions [16 17] These areinfluenced by the chemical structure of the inhibitor the typeof the electrolyte pH the charge and nature of the metal andtemperature [18] The phenomenon of interaction betweenthe metal surface and the inhibitor can be better understoodin terms of adsorption isothermThe plots of119862inh120579 against119862(Figure 6) yield a straight line with approximately unit slopeindicating that the inhibitor under study obeys Langmuiradsorption isotherm According to this isotherm 120579 is relatedto 119862inh by [19]
119862inh120579
=
1
119870ads+ 119862inh (5)
0 1 2 3 4 5 6
980
975
790
965
960
955
950
945
IE (
)
Time (h)
Figure 3 Variation of inhibition efficiency of KI with immersiontime
15
00
minus15
minus30
minus45
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
)(m
gcm
2middoth)
Figure 4 Adsorption isotherm plots for ln 119908 versus 1119879
minus45
minus60
minus75
minus90
minus105
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
T)(m
gcm
2middothmiddotK)
Figure 5 Adsorption isotherm plots for ln(119908119879) versus 1119879
4 Advances in Chemistry
20
15
10
05
00 05 10 15 20
Cinh (molL) times10minus3
times10minus3
Cin
h120579
(mol
L)
Figure 6 Relationship between (119862inh120579) and inhibitor concentra-tion 119862inh
The119870ads values can be calculated from the intercept lineson the 119862inh120579-axis This is related to the standard free energyof adsorption (Δ119866ads) with the following equation [20]
119870ads = (1
555
) exp(minusΔ119866ads119877119879
) (6)
where
Δ119866ads = minus119877119879 ln (555119870ads) (7)
where119877 is the gas constant and119879 is the absolute temperatureThe constant value of 555 is the concentration of water insolution in moldm3 [21]
The intercept permits the calculation of the equilib-rium constant 119870ads which is 617 times 104 Lmol respectivelyThe value of 119870ads which indicates the binding power ofthe inhibitor to the pure iron surface leads to calcula-tion of adsorption energy Value of Δ119866ads is minus3755 kJmolrespectively The negative values of Δ119866ads showed that theadsorption of inhibitor molecules on the metal surface isspontaneous [22]
Generally the standard free energy values of minus20 kJmolor less negative are associated with an electrostatic interac-tion between charged molecules and charged metal surface(physical adsorption) those of minus40 kJmol or more nega-tive involves charge sharing or transfer from the inhibitormolecules to the metal surface to form a co-ordinate covalentbond (chemical adsorption)
Note that our measures were carried out without inertatmosphere In 1M H+ the iodide ion becomes hydrogeniodide which reacts with oxygen to form molecule iodideI2 The formed molecule could be adsorbed onto iron and
occupying the surface it strikes the adsorption of iodideAt the end a lower efficiency of adsorption of iodide wasobtained but the inhibition efficiency of the studied inhibitorKI increases due to adsorption of I
2
Otherwise the value of Δ119866ads (minus3755 kJmol) near tominus40 kJmol indicates that in our case the adsorption isneither typical chemisorption nor typical physisorption but
it is a complex mixed type That is the adsorption inhibitormolecule on the iron surface in the present study involvesboth chemisorption (of I
2) and physisorption (of Iminus) but
chemisorption is the predominant mode of adsorptionThis assumption is supported by the data obtained fromtemperature dependence of inhibition process reported inTables 2 and 3 which show that the inhibition efficiency ofthe studied compound as inhibitor increases with increasein temperature and that the value of 119864
119886in absence of the
inhibitor is lower than that in its presence [23] On the otherhand it is known that the iron surface acquires positive chargein H2SO405M [24] while iodide ion is negatively charged
as a result the physisorption (electrostatic attraction) of theiodide ion occurs onto iron surface
4 Conclusion
On the basis of the experimental results obtained in thepresent study the following conclusions can be drawn
(1) Potassium iodide is a good inhibitor for pure ironcorrosion in 05M H
2SO4solution The inhibition
efficiency increases with increased KI concentrationto attain a maximum value of 9751 at 2sdot10minus3M
(2) The adsorption of KI on pure iron obeyed Langmuiradsorption isotherm
(3) At higher experimental temperature inhibitormolecules are adsorbed into the metal surface
(4) The negative value of Δ119866ads is a sign of spontaneousadsorption on the metal surface
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] B Eker and E Yuksel ldquoSolutions to corrosion caused byagricultural chemicalsrdquo Trakia Journal of Sciences vol 3 no 7pp 1ndash6 2005
[2] N Patni S Agarwal and P Shah ldquoGreener Approach towardsCorrosion Inhibitionrdquo Chinese Journal of Engineering vol 2013Article ID 784186 10 pages 2013
[3] T H Ibrahim and M A Zour ldquoCorrosion inhibition of mildsteel using fig leaves extract in hydrochloric acid solutionrdquoInternational Journal of Electrochemical Science vol 6 no 12pp 6442ndash6455 2011
[4] E-S M Sherif ldquoElectrochemical and gravimetric study on thecorrosion and corrosion inhibition of pure copper in sodiumchloride solutions by two azole derivativesrdquo International Jour-nal of Electrochemical Science vol 7 no 2 pp 1482ndash1495 2012
[5] P Rajeev A O Surendranathan and C S N Murthy ldquoCorro-sion mitigation of the oil well steels using organic inhibitorsmdashareviewrdquo Journal of Materials and Environmental Science vol 3no 5 pp 856ndash869 2012
Advances in Chemistry 5
[6] E-S M Sherif ldquoCorrosion and corrosion inhibitionof pure iron in neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquo International Journal ofElectrochemical Science vol 6 no 8 pp 3077ndash3092 2011
[7] H Amar A Tounsi A Makayssi A Derja J Benzakour andA Outzourhit ldquoCorrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3 mediardquo Corro-sion Science vol 49 no 7 pp 2936ndash2945 2007
[8] E-SM Sherif RM Erasmus and JD Comins ldquoIn situ Ramanspectroscopy and electrochemical techniques for studying cor-rosion and corrosion inhibition of iron in sodium chloridesolutionsrdquo Electrochimica Acta vol 55 no 11 pp 3657ndash36632010
[9] E SM Sherif ldquoCorrosion and corrosion inhibition of pure ironin neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquoInternational Journal of Electrochemical Science vol 6 pp 3077ndash3092 2011
[10] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012
[11] T Poornima N Jagannatha and A Nityananda Shetty ldquoStudieson corrosion of annealed and aged 18 Ni 250 grade maragingsteel in sulphuric acid mediumrdquo Portugaliae ElectrochimicaActa vol 28 no 3 pp 173ndash188 2010
[12] P Kumar and A N Shetty ldquoElectrochemical investigation onthe corrosion of 18Ni M250 grade maraging steel underwelded condition in sulfuric acid mediumrdquo Surface Engineeringand Applied Electrochemistry vol 49 no 3 pp 253ndash260 2013
[13] I Lukovits E Kalman and F Zucchi ldquoCorrosion inhibitorsmdashcorrelation between electronic structure and efficiencyrdquo Corro-sion vol 57 no 1 pp 3ndash8 2001
[14] M A Quraishi and S Khan ldquoThiadiazoles-A potential class ofheterocyclic inhibitors for prevention of mild steel corrosionin hydrochloric acid solutionrdquo Indian Journal of ChemicalTechnology vol 12 no 5 pp 576ndash581 2005
[15] E A Noor and A H Al-Moubaraki ldquoThermodynamicstudy of metal corrosion and inhibitor adsorptionprocesses in mild steel1-methyl-4[41015840(-X)-styryl pyridiniumiodideshydrochloric acid systemsrdquo Materials Chemistry andPhysics vol 110 no 1 pp 145ndash154 2008
[16] L Larabi O Benali and Y Harek ldquoCorrosion inhibition ofcopper in 1 M HNO
3solution by N-phenyl oxalic dihydrazide
and oxalic N-phenylhydrazide 1198731015840-phenylthiosemicarbaziderdquoPortugaliae Electrochimica Acta vol 24 no 3 pp 337ndash3462006
[17] L Larabi Y Harek M Traisnel and A Mansri ldquoSynergisticinfluence of poly(4-vinylpyridine) and potassium iodide oninhibition of corrosion of mild steel in 1M HClrdquo Journal ofApplied Electrochemistry vol 34 no 8 pp 833ndash839 2004
[18] M A Ameer and A M Fekry ldquoInhibition effect of newlysynthesized heterocyclic organicmolecules on corrosion of steelin alkaline medium containing chloriderdquo International Journalof Hydrogen Energy vol 35 no 20 pp 11387ndash11396 2010
[19] M Benabdellah A Aouniti A Dafali et al ldquoInvestigation ofthe inhibitive effect of triphenyltin 2-thiophene carboxylate oncorrosion of steel in 2 M H
3PO4solutionsrdquo Applied Surface
Science vol 252 no 23 pp 8341ndash8347 2006[20] A M Fekry and M A Ameer ldquoCorrosion inhibition of mild
steel in acidic media using newly synthesized heterocyclicorganic moleculesrdquo International Journal of Hydrogen Energyvol 35 no 14 pp 7641ndash7651 2010
[21] O Olivares N V Likhanova B Gomez et al ldquoElectrochemicaland XPS studies of decylamides of 120572-amino acids adsorptionon carbon steel in acidic environmentrdquo Applied Surface Sciencevol 252 no 8 pp 2894ndash2909 2006
[22] A Dabrowski ldquoAdsorption-from theory to practicerdquo Advancesin Colloid and Interface Science vol 93 no 1ndash3 pp 135ndash2242001
[23] T Szauer and A Brandt ldquoOn the role of fatty acid in adsorptionand corrosion inhibition of iron by amine-fatty acid salts inacidic solutionrdquo Electrochimica Acta vol 26 no 9 pp 1257ndash1260 1981
[24] B S Prathibha P Kottees waram and R V Bheema ldquoStudyon the inhibition of mild steel corrosion by quaterwareyAmmonium compound in H
2SO4mediumrdquo Research Journal of
Recent Sciences vol 2 no 4 pp 1ndash10 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Advances in Chemistry 3
Table 1 Corrosion parameters for pure iron in aqueous solution of05MH2SO4 in presence and absence of different concentrations ofKI at 303K for 2 h
119862 (molL) 119908 (mgsdotcmminus2sdothminus1) IE ()H2SO4 05 160383 mdash
KI
1 sdot 10
minus4 028593 821725 sdot 10
minus4 010956 93165 sdot 10
minus4 007787 951575 sdot 10
minus4 005445 96601 sdot 10
minus3 004169 97112 sdot 10
minus3 003986 9751
Table 2 Effect of temperature on pure iron in the presence andabsence of KI at 2 h
119879 (K) 119908
0(mgcm2
sdoth1) 119908inh (mgcm2sdoth1) IE ()
293 015107 000622 9588303 034152 001329 9610313 132256 005035 9619323 343109 011280 9671
Table 3 The values of activation parameters for pure iron in05MH2SO4 in the absence and the presence of inhibitor of 2sdot10
minus3Mconcentration at 2 h
Concentrationof inhibitor (M)
119864
119886
(kJmol)Δ119867
119886
(kJmol)119864
119886minus Δ119867
119886
(kJmol)05H2SO4 8432 8165 2672 sdot 10
minus3 KI 7889 7622 267
Aplot of ln(119908119879) versus 1119879 gave a straight line (Figure 5)with a slope of minus(Δ119867
119886119877) from which the value of Δ119867
119886was
calculated and listed in Table 3The 119864
119886values in the presence of inhibitor are lower than
in the absence of inhibitor indicating that the inhibition effi-ciency increases with increases in temperature The positivesign of enthalpy of activation reflects the endothermic natureof the steel dissolution process
34 Adsorption Isotherm Adsorption isotherms provideinformation about the interaction of the adsorbed moleculeswith the electrode surface [15] The adsorption of theinhibitors can be described by two main types of interactionphysical adsorption and chemisorptions [16 17] These areinfluenced by the chemical structure of the inhibitor the typeof the electrolyte pH the charge and nature of the metal andtemperature [18] The phenomenon of interaction betweenthe metal surface and the inhibitor can be better understoodin terms of adsorption isothermThe plots of119862inh120579 against119862(Figure 6) yield a straight line with approximately unit slopeindicating that the inhibitor under study obeys Langmuiradsorption isotherm According to this isotherm 120579 is relatedto 119862inh by [19]
119862inh120579
=
1
119870ads+ 119862inh (5)
0 1 2 3 4 5 6
980
975
790
965
960
955
950
945
IE (
)
Time (h)
Figure 3 Variation of inhibition efficiency of KI with immersiontime
15
00
minus15
minus30
minus45
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
)(m
gcm
2middoth)
Figure 4 Adsorption isotherm plots for ln 119908 versus 1119879
minus45
minus60
minus75
minus90
minus105
31 32 32 33 34 34
times10minus3
H2SO4 05MKI 210minus3 M
1T (Kminus1)
Ln(W
T)(m
gcm
2middothmiddotK)
Figure 5 Adsorption isotherm plots for ln(119908119879) versus 1119879
4 Advances in Chemistry
20
15
10
05
00 05 10 15 20
Cinh (molL) times10minus3
times10minus3
Cin
h120579
(mol
L)
Figure 6 Relationship between (119862inh120579) and inhibitor concentra-tion 119862inh
The119870ads values can be calculated from the intercept lineson the 119862inh120579-axis This is related to the standard free energyof adsorption (Δ119866ads) with the following equation [20]
119870ads = (1
555
) exp(minusΔ119866ads119877119879
) (6)
where
Δ119866ads = minus119877119879 ln (555119870ads) (7)
where119877 is the gas constant and119879 is the absolute temperatureThe constant value of 555 is the concentration of water insolution in moldm3 [21]
The intercept permits the calculation of the equilib-rium constant 119870ads which is 617 times 104 Lmol respectivelyThe value of 119870ads which indicates the binding power ofthe inhibitor to the pure iron surface leads to calcula-tion of adsorption energy Value of Δ119866ads is minus3755 kJmolrespectively The negative values of Δ119866ads showed that theadsorption of inhibitor molecules on the metal surface isspontaneous [22]
Generally the standard free energy values of minus20 kJmolor less negative are associated with an electrostatic interac-tion between charged molecules and charged metal surface(physical adsorption) those of minus40 kJmol or more nega-tive involves charge sharing or transfer from the inhibitormolecules to the metal surface to form a co-ordinate covalentbond (chemical adsorption)
Note that our measures were carried out without inertatmosphere In 1M H+ the iodide ion becomes hydrogeniodide which reacts with oxygen to form molecule iodideI2 The formed molecule could be adsorbed onto iron and
occupying the surface it strikes the adsorption of iodideAt the end a lower efficiency of adsorption of iodide wasobtained but the inhibition efficiency of the studied inhibitorKI increases due to adsorption of I
2
Otherwise the value of Δ119866ads (minus3755 kJmol) near tominus40 kJmol indicates that in our case the adsorption isneither typical chemisorption nor typical physisorption but
it is a complex mixed type That is the adsorption inhibitormolecule on the iron surface in the present study involvesboth chemisorption (of I
2) and physisorption (of Iminus) but
chemisorption is the predominant mode of adsorptionThis assumption is supported by the data obtained fromtemperature dependence of inhibition process reported inTables 2 and 3 which show that the inhibition efficiency ofthe studied compound as inhibitor increases with increasein temperature and that the value of 119864
119886in absence of the
inhibitor is lower than that in its presence [23] On the otherhand it is known that the iron surface acquires positive chargein H2SO405M [24] while iodide ion is negatively charged
as a result the physisorption (electrostatic attraction) of theiodide ion occurs onto iron surface
4 Conclusion
On the basis of the experimental results obtained in thepresent study the following conclusions can be drawn
(1) Potassium iodide is a good inhibitor for pure ironcorrosion in 05M H
2SO4solution The inhibition
efficiency increases with increased KI concentrationto attain a maximum value of 9751 at 2sdot10minus3M
(2) The adsorption of KI on pure iron obeyed Langmuiradsorption isotherm
(3) At higher experimental temperature inhibitormolecules are adsorbed into the metal surface
(4) The negative value of Δ119866ads is a sign of spontaneousadsorption on the metal surface
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] B Eker and E Yuksel ldquoSolutions to corrosion caused byagricultural chemicalsrdquo Trakia Journal of Sciences vol 3 no 7pp 1ndash6 2005
[2] N Patni S Agarwal and P Shah ldquoGreener Approach towardsCorrosion Inhibitionrdquo Chinese Journal of Engineering vol 2013Article ID 784186 10 pages 2013
[3] T H Ibrahim and M A Zour ldquoCorrosion inhibition of mildsteel using fig leaves extract in hydrochloric acid solutionrdquoInternational Journal of Electrochemical Science vol 6 no 12pp 6442ndash6455 2011
[4] E-S M Sherif ldquoElectrochemical and gravimetric study on thecorrosion and corrosion inhibition of pure copper in sodiumchloride solutions by two azole derivativesrdquo International Jour-nal of Electrochemical Science vol 7 no 2 pp 1482ndash1495 2012
[5] P Rajeev A O Surendranathan and C S N Murthy ldquoCorro-sion mitigation of the oil well steels using organic inhibitorsmdashareviewrdquo Journal of Materials and Environmental Science vol 3no 5 pp 856ndash869 2012
Advances in Chemistry 5
[6] E-S M Sherif ldquoCorrosion and corrosion inhibitionof pure iron in neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquo International Journal ofElectrochemical Science vol 6 no 8 pp 3077ndash3092 2011
[7] H Amar A Tounsi A Makayssi A Derja J Benzakour andA Outzourhit ldquoCorrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3 mediardquo Corro-sion Science vol 49 no 7 pp 2936ndash2945 2007
[8] E-SM Sherif RM Erasmus and JD Comins ldquoIn situ Ramanspectroscopy and electrochemical techniques for studying cor-rosion and corrosion inhibition of iron in sodium chloridesolutionsrdquo Electrochimica Acta vol 55 no 11 pp 3657ndash36632010
[9] E SM Sherif ldquoCorrosion and corrosion inhibition of pure ironin neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquoInternational Journal of Electrochemical Science vol 6 pp 3077ndash3092 2011
[10] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012
[11] T Poornima N Jagannatha and A Nityananda Shetty ldquoStudieson corrosion of annealed and aged 18 Ni 250 grade maragingsteel in sulphuric acid mediumrdquo Portugaliae ElectrochimicaActa vol 28 no 3 pp 173ndash188 2010
[12] P Kumar and A N Shetty ldquoElectrochemical investigation onthe corrosion of 18Ni M250 grade maraging steel underwelded condition in sulfuric acid mediumrdquo Surface Engineeringand Applied Electrochemistry vol 49 no 3 pp 253ndash260 2013
[13] I Lukovits E Kalman and F Zucchi ldquoCorrosion inhibitorsmdashcorrelation between electronic structure and efficiencyrdquo Corro-sion vol 57 no 1 pp 3ndash8 2001
[14] M A Quraishi and S Khan ldquoThiadiazoles-A potential class ofheterocyclic inhibitors for prevention of mild steel corrosionin hydrochloric acid solutionrdquo Indian Journal of ChemicalTechnology vol 12 no 5 pp 576ndash581 2005
[15] E A Noor and A H Al-Moubaraki ldquoThermodynamicstudy of metal corrosion and inhibitor adsorptionprocesses in mild steel1-methyl-4[41015840(-X)-styryl pyridiniumiodideshydrochloric acid systemsrdquo Materials Chemistry andPhysics vol 110 no 1 pp 145ndash154 2008
[16] L Larabi O Benali and Y Harek ldquoCorrosion inhibition ofcopper in 1 M HNO
3solution by N-phenyl oxalic dihydrazide
and oxalic N-phenylhydrazide 1198731015840-phenylthiosemicarbaziderdquoPortugaliae Electrochimica Acta vol 24 no 3 pp 337ndash3462006
[17] L Larabi Y Harek M Traisnel and A Mansri ldquoSynergisticinfluence of poly(4-vinylpyridine) and potassium iodide oninhibition of corrosion of mild steel in 1M HClrdquo Journal ofApplied Electrochemistry vol 34 no 8 pp 833ndash839 2004
[18] M A Ameer and A M Fekry ldquoInhibition effect of newlysynthesized heterocyclic organicmolecules on corrosion of steelin alkaline medium containing chloriderdquo International Journalof Hydrogen Energy vol 35 no 20 pp 11387ndash11396 2010
[19] M Benabdellah A Aouniti A Dafali et al ldquoInvestigation ofthe inhibitive effect of triphenyltin 2-thiophene carboxylate oncorrosion of steel in 2 M H
3PO4solutionsrdquo Applied Surface
Science vol 252 no 23 pp 8341ndash8347 2006[20] A M Fekry and M A Ameer ldquoCorrosion inhibition of mild
steel in acidic media using newly synthesized heterocyclicorganic moleculesrdquo International Journal of Hydrogen Energyvol 35 no 14 pp 7641ndash7651 2010
[21] O Olivares N V Likhanova B Gomez et al ldquoElectrochemicaland XPS studies of decylamides of 120572-amino acids adsorptionon carbon steel in acidic environmentrdquo Applied Surface Sciencevol 252 no 8 pp 2894ndash2909 2006
[22] A Dabrowski ldquoAdsorption-from theory to practicerdquo Advancesin Colloid and Interface Science vol 93 no 1ndash3 pp 135ndash2242001
[23] T Szauer and A Brandt ldquoOn the role of fatty acid in adsorptionand corrosion inhibition of iron by amine-fatty acid salts inacidic solutionrdquo Electrochimica Acta vol 26 no 9 pp 1257ndash1260 1981
[24] B S Prathibha P Kottees waram and R V Bheema ldquoStudyon the inhibition of mild steel corrosion by quaterwareyAmmonium compound in H
2SO4mediumrdquo Research Journal of
Recent Sciences vol 2 no 4 pp 1ndash10 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 Advances in Chemistry
20
15
10
05
00 05 10 15 20
Cinh (molL) times10minus3
times10minus3
Cin
h120579
(mol
L)
Figure 6 Relationship between (119862inh120579) and inhibitor concentra-tion 119862inh
The119870ads values can be calculated from the intercept lineson the 119862inh120579-axis This is related to the standard free energyof adsorption (Δ119866ads) with the following equation [20]
119870ads = (1
555
) exp(minusΔ119866ads119877119879
) (6)
where
Δ119866ads = minus119877119879 ln (555119870ads) (7)
where119877 is the gas constant and119879 is the absolute temperatureThe constant value of 555 is the concentration of water insolution in moldm3 [21]
The intercept permits the calculation of the equilib-rium constant 119870ads which is 617 times 104 Lmol respectivelyThe value of 119870ads which indicates the binding power ofthe inhibitor to the pure iron surface leads to calcula-tion of adsorption energy Value of Δ119866ads is minus3755 kJmolrespectively The negative values of Δ119866ads showed that theadsorption of inhibitor molecules on the metal surface isspontaneous [22]
Generally the standard free energy values of minus20 kJmolor less negative are associated with an electrostatic interac-tion between charged molecules and charged metal surface(physical adsorption) those of minus40 kJmol or more nega-tive involves charge sharing or transfer from the inhibitormolecules to the metal surface to form a co-ordinate covalentbond (chemical adsorption)
Note that our measures were carried out without inertatmosphere In 1M H+ the iodide ion becomes hydrogeniodide which reacts with oxygen to form molecule iodideI2 The formed molecule could be adsorbed onto iron and
occupying the surface it strikes the adsorption of iodideAt the end a lower efficiency of adsorption of iodide wasobtained but the inhibition efficiency of the studied inhibitorKI increases due to adsorption of I
2
Otherwise the value of Δ119866ads (minus3755 kJmol) near tominus40 kJmol indicates that in our case the adsorption isneither typical chemisorption nor typical physisorption but
it is a complex mixed type That is the adsorption inhibitormolecule on the iron surface in the present study involvesboth chemisorption (of I
2) and physisorption (of Iminus) but
chemisorption is the predominant mode of adsorptionThis assumption is supported by the data obtained fromtemperature dependence of inhibition process reported inTables 2 and 3 which show that the inhibition efficiency ofthe studied compound as inhibitor increases with increasein temperature and that the value of 119864
119886in absence of the
inhibitor is lower than that in its presence [23] On the otherhand it is known that the iron surface acquires positive chargein H2SO405M [24] while iodide ion is negatively charged
as a result the physisorption (electrostatic attraction) of theiodide ion occurs onto iron surface
4 Conclusion
On the basis of the experimental results obtained in thepresent study the following conclusions can be drawn
(1) Potassium iodide is a good inhibitor for pure ironcorrosion in 05M H
2SO4solution The inhibition
efficiency increases with increased KI concentrationto attain a maximum value of 9751 at 2sdot10minus3M
(2) The adsorption of KI on pure iron obeyed Langmuiradsorption isotherm
(3) At higher experimental temperature inhibitormolecules are adsorbed into the metal surface
(4) The negative value of Δ119866ads is a sign of spontaneousadsorption on the metal surface
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] B Eker and E Yuksel ldquoSolutions to corrosion caused byagricultural chemicalsrdquo Trakia Journal of Sciences vol 3 no 7pp 1ndash6 2005
[2] N Patni S Agarwal and P Shah ldquoGreener Approach towardsCorrosion Inhibitionrdquo Chinese Journal of Engineering vol 2013Article ID 784186 10 pages 2013
[3] T H Ibrahim and M A Zour ldquoCorrosion inhibition of mildsteel using fig leaves extract in hydrochloric acid solutionrdquoInternational Journal of Electrochemical Science vol 6 no 12pp 6442ndash6455 2011
[4] E-S M Sherif ldquoElectrochemical and gravimetric study on thecorrosion and corrosion inhibition of pure copper in sodiumchloride solutions by two azole derivativesrdquo International Jour-nal of Electrochemical Science vol 7 no 2 pp 1482ndash1495 2012
[5] P Rajeev A O Surendranathan and C S N Murthy ldquoCorro-sion mitigation of the oil well steels using organic inhibitorsmdashareviewrdquo Journal of Materials and Environmental Science vol 3no 5 pp 856ndash869 2012
Advances in Chemistry 5
[6] E-S M Sherif ldquoCorrosion and corrosion inhibitionof pure iron in neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquo International Journal ofElectrochemical Science vol 6 no 8 pp 3077ndash3092 2011
[7] H Amar A Tounsi A Makayssi A Derja J Benzakour andA Outzourhit ldquoCorrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3 mediardquo Corro-sion Science vol 49 no 7 pp 2936ndash2945 2007
[8] E-SM Sherif RM Erasmus and JD Comins ldquoIn situ Ramanspectroscopy and electrochemical techniques for studying cor-rosion and corrosion inhibition of iron in sodium chloridesolutionsrdquo Electrochimica Acta vol 55 no 11 pp 3657ndash36632010
[9] E SM Sherif ldquoCorrosion and corrosion inhibition of pure ironin neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquoInternational Journal of Electrochemical Science vol 6 pp 3077ndash3092 2011
[10] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012
[11] T Poornima N Jagannatha and A Nityananda Shetty ldquoStudieson corrosion of annealed and aged 18 Ni 250 grade maragingsteel in sulphuric acid mediumrdquo Portugaliae ElectrochimicaActa vol 28 no 3 pp 173ndash188 2010
[12] P Kumar and A N Shetty ldquoElectrochemical investigation onthe corrosion of 18Ni M250 grade maraging steel underwelded condition in sulfuric acid mediumrdquo Surface Engineeringand Applied Electrochemistry vol 49 no 3 pp 253ndash260 2013
[13] I Lukovits E Kalman and F Zucchi ldquoCorrosion inhibitorsmdashcorrelation between electronic structure and efficiencyrdquo Corro-sion vol 57 no 1 pp 3ndash8 2001
[14] M A Quraishi and S Khan ldquoThiadiazoles-A potential class ofheterocyclic inhibitors for prevention of mild steel corrosionin hydrochloric acid solutionrdquo Indian Journal of ChemicalTechnology vol 12 no 5 pp 576ndash581 2005
[15] E A Noor and A H Al-Moubaraki ldquoThermodynamicstudy of metal corrosion and inhibitor adsorptionprocesses in mild steel1-methyl-4[41015840(-X)-styryl pyridiniumiodideshydrochloric acid systemsrdquo Materials Chemistry andPhysics vol 110 no 1 pp 145ndash154 2008
[16] L Larabi O Benali and Y Harek ldquoCorrosion inhibition ofcopper in 1 M HNO
3solution by N-phenyl oxalic dihydrazide
and oxalic N-phenylhydrazide 1198731015840-phenylthiosemicarbaziderdquoPortugaliae Electrochimica Acta vol 24 no 3 pp 337ndash3462006
[17] L Larabi Y Harek M Traisnel and A Mansri ldquoSynergisticinfluence of poly(4-vinylpyridine) and potassium iodide oninhibition of corrosion of mild steel in 1M HClrdquo Journal ofApplied Electrochemistry vol 34 no 8 pp 833ndash839 2004
[18] M A Ameer and A M Fekry ldquoInhibition effect of newlysynthesized heterocyclic organicmolecules on corrosion of steelin alkaline medium containing chloriderdquo International Journalof Hydrogen Energy vol 35 no 20 pp 11387ndash11396 2010
[19] M Benabdellah A Aouniti A Dafali et al ldquoInvestigation ofthe inhibitive effect of triphenyltin 2-thiophene carboxylate oncorrosion of steel in 2 M H
3PO4solutionsrdquo Applied Surface
Science vol 252 no 23 pp 8341ndash8347 2006[20] A M Fekry and M A Ameer ldquoCorrosion inhibition of mild
steel in acidic media using newly synthesized heterocyclicorganic moleculesrdquo International Journal of Hydrogen Energyvol 35 no 14 pp 7641ndash7651 2010
[21] O Olivares N V Likhanova B Gomez et al ldquoElectrochemicaland XPS studies of decylamides of 120572-amino acids adsorptionon carbon steel in acidic environmentrdquo Applied Surface Sciencevol 252 no 8 pp 2894ndash2909 2006
[22] A Dabrowski ldquoAdsorption-from theory to practicerdquo Advancesin Colloid and Interface Science vol 93 no 1ndash3 pp 135ndash2242001
[23] T Szauer and A Brandt ldquoOn the role of fatty acid in adsorptionand corrosion inhibition of iron by amine-fatty acid salts inacidic solutionrdquo Electrochimica Acta vol 26 no 9 pp 1257ndash1260 1981
[24] B S Prathibha P Kottees waram and R V Bheema ldquoStudyon the inhibition of mild steel corrosion by quaterwareyAmmonium compound in H
2SO4mediumrdquo Research Journal of
Recent Sciences vol 2 no 4 pp 1ndash10 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Advances in Chemistry 5
[6] E-S M Sherif ldquoCorrosion and corrosion inhibitionof pure iron in neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquo International Journal ofElectrochemical Science vol 6 no 8 pp 3077ndash3092 2011
[7] H Amar A Tounsi A Makayssi A Derja J Benzakour andA Outzourhit ldquoCorrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3 mediardquo Corro-sion Science vol 49 no 7 pp 2936ndash2945 2007
[8] E-SM Sherif RM Erasmus and JD Comins ldquoIn situ Ramanspectroscopy and electrochemical techniques for studying cor-rosion and corrosion inhibition of iron in sodium chloridesolutionsrdquo Electrochimica Acta vol 55 no 11 pp 3657ndash36632010
[9] E SM Sherif ldquoCorrosion and corrosion inhibition of pure ironin neutral chloride solutions by 111015840-thiocarbonyldiimidazolerdquoInternational Journal of Electrochemical Science vol 6 pp 3077ndash3092 2011
[10] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012
[11] T Poornima N Jagannatha and A Nityananda Shetty ldquoStudieson corrosion of annealed and aged 18 Ni 250 grade maragingsteel in sulphuric acid mediumrdquo Portugaliae ElectrochimicaActa vol 28 no 3 pp 173ndash188 2010
[12] P Kumar and A N Shetty ldquoElectrochemical investigation onthe corrosion of 18Ni M250 grade maraging steel underwelded condition in sulfuric acid mediumrdquo Surface Engineeringand Applied Electrochemistry vol 49 no 3 pp 253ndash260 2013
[13] I Lukovits E Kalman and F Zucchi ldquoCorrosion inhibitorsmdashcorrelation between electronic structure and efficiencyrdquo Corro-sion vol 57 no 1 pp 3ndash8 2001
[14] M A Quraishi and S Khan ldquoThiadiazoles-A potential class ofheterocyclic inhibitors for prevention of mild steel corrosionin hydrochloric acid solutionrdquo Indian Journal of ChemicalTechnology vol 12 no 5 pp 576ndash581 2005
[15] E A Noor and A H Al-Moubaraki ldquoThermodynamicstudy of metal corrosion and inhibitor adsorptionprocesses in mild steel1-methyl-4[41015840(-X)-styryl pyridiniumiodideshydrochloric acid systemsrdquo Materials Chemistry andPhysics vol 110 no 1 pp 145ndash154 2008
[16] L Larabi O Benali and Y Harek ldquoCorrosion inhibition ofcopper in 1 M HNO
3solution by N-phenyl oxalic dihydrazide
and oxalic N-phenylhydrazide 1198731015840-phenylthiosemicarbaziderdquoPortugaliae Electrochimica Acta vol 24 no 3 pp 337ndash3462006
[17] L Larabi Y Harek M Traisnel and A Mansri ldquoSynergisticinfluence of poly(4-vinylpyridine) and potassium iodide oninhibition of corrosion of mild steel in 1M HClrdquo Journal ofApplied Electrochemistry vol 34 no 8 pp 833ndash839 2004
[18] M A Ameer and A M Fekry ldquoInhibition effect of newlysynthesized heterocyclic organicmolecules on corrosion of steelin alkaline medium containing chloriderdquo International Journalof Hydrogen Energy vol 35 no 20 pp 11387ndash11396 2010
[19] M Benabdellah A Aouniti A Dafali et al ldquoInvestigation ofthe inhibitive effect of triphenyltin 2-thiophene carboxylate oncorrosion of steel in 2 M H
3PO4solutionsrdquo Applied Surface
Science vol 252 no 23 pp 8341ndash8347 2006[20] A M Fekry and M A Ameer ldquoCorrosion inhibition of mild
steel in acidic media using newly synthesized heterocyclicorganic moleculesrdquo International Journal of Hydrogen Energyvol 35 no 14 pp 7641ndash7651 2010
[21] O Olivares N V Likhanova B Gomez et al ldquoElectrochemicaland XPS studies of decylamides of 120572-amino acids adsorptionon carbon steel in acidic environmentrdquo Applied Surface Sciencevol 252 no 8 pp 2894ndash2909 2006
[22] A Dabrowski ldquoAdsorption-from theory to practicerdquo Advancesin Colloid and Interface Science vol 93 no 1ndash3 pp 135ndash2242001
[23] T Szauer and A Brandt ldquoOn the role of fatty acid in adsorptionand corrosion inhibition of iron by amine-fatty acid salts inacidic solutionrdquo Electrochimica Acta vol 26 no 9 pp 1257ndash1260 1981
[24] B S Prathibha P Kottees waram and R V Bheema ldquoStudyon the inhibition of mild steel corrosion by quaterwareyAmmonium compound in H
2SO4mediumrdquo Research Journal of
Recent Sciences vol 2 no 4 pp 1ndash10 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of