Research Article Anodic Dissolution of Spheroidal Graphite Cast … · 2019. 7. 31. ·...

Hindawi Publishing CorporationInternational Journal of CorrosionVolume 2013 Article ID 741378 7 pageshttpdxdoiorg1011552013741378

Research ArticleAnodic Dissolution of Spheroidal Graphite Cast Iron withDifferent Pearlite Areas in Sulfuric Acid Solutions

Yoshikazu Miyata1 Yuki Kuwahara12 Shukuji Asakura1 Tadashi Shinohara13

Takao Yakou1 and Keiichi Shiimoto2

1 Graduate School of Engineering Yokohama National University 79-5 Tokiwadai Hodogaya-ku Yokohama 240-8501 Japan2Hinode Suido Ltd 5-8-18 Katakasu Hakata-ku Fukuoka 812-8636 Japan3National Institute for Materials Science 1-2-1 Sengen Tsukuba Ibaraki 305-0047 Japan

Correspondence should be addressed to Yoshikazu Miyata ymiyataynuacjp

Received 10 July 2013 Revised 3 September 2013 Accepted 16 September 2013

Academic Editor W Ke

Copyright copy 2013 Yoshikazu Miyata et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The rate equation of anodic dissolution reaction of spheroidal graphite cast iron in sulfuric acid solutions at 298K has been studiedThe cast irons have different areas of pearlite The anodic Tafel slope of 0043V decademinus1 and the reaction order with respect to thehydroxyl ion activity of 1 are obtained by the linear potential sweep technique The anodic current density does not depend on thearea of pearlite There is no difference in the anodic dissolution reaction mechanisms between pure iron and spheroidal graphitecast iron The anodic current density of the cast iron is higher than that of the pure iron

1 Introduction

Cast iron is widely used for pipes in neutral environmentssuch as water and soil A lot of experimental studies ofcast iron for practical use were conducted [1ndash8] A form ofcorrosion unique to cast irons is a selective leaching attackcommonly referred to as graphitic corrosion [9 page 89] Agraphite network forms a corrosion-resistant phase called agraphitic layerTherefore the corrosion resistance of cast ironis said to be higher than that of steel That is not necessarilythe case

Laque reported that the corrosion rate of cast irons islower than that of a steel in the atmosphere above the sea[2] However Paris and Bruniere [1] and Horikawa et al [10]found that the corrosion rate of cast irons is nearly equal tothat of steel in water and in atmosphere Furthermore a booksaid that graphitic corrosion does not occur in spheroidalgraphite cast irons because the graphite network does notexist [9 page 89] while another author reported that it occurswith both gray and spheroidal graphite cast irons [11] Theseinconsistent results come from the complexity of graphiticcorrosion To elucidate the mechanisms of corrosion of

cast iron intensive studies are required In this paper theelectrochemical dissolution of ferrous matrix is discussed

Cast iron is composed of pearlitic matrix ferritic matrixand graphite particles The area of pearlite influences thephysical properties such as tensile strength elongation andhardness [12] Pearlitic matrix is a lamellar mixture of ferriteand cementite Thus the length of interfaces between ferriteand cementite becomes large with increasing pearlite areaFontana [9 pages 28ndash31] and Trethewey and Chamberlain[13] described in their books that grain boundaries are high-energy areas and are more active chemically The book byEvans said that regions near the grain boundariesmay possesselectrochemical properties different from those of the graininteriors [14] Therefore the area of pearlite may influencethe mechanism and the rate of anodic dissolution of ferrousmatrix

To the authorsrsquo knowledge there are few studies on thedissolution reaction mechanism of cast ironThe objective ofthe present investigation is to determine the kinetic param-eters and the rate equation of anodic dissolution reaction ofspheroidal graphite cast iron having different areas of pearlitein sulfuric acid solutions

2 International Journal of Corrosion

Table 1 Chemical composition of the spheroidal graphite cast iron(mass)

C Si Mn P S Cu Mg367 199 041 0013 001 019 0046

Table 2 Ratios of the pearlite area the graphite particles area andthe ferrite area

Specimen no 119875119903

119866119903

119865119903

(1) (2) (3)1 0 021 0792 008 019 0773 029 020 0654 057 018 054The ratios of the pearlite area 119875

119903

the graphite particles area 119866119903

and theferrite area 119865

119903

are defined by (1) (2) and (3) respectively

2 Experimental

21 Specimen The chemical composition of specimens ofspheroidal graphite cast iron (hereinafter referred to as castiron) is given in Table 1 Cast irons which have different areasof pearlite were prepared A sand mold given in Figure 1was used for casting Specimens were clipped from the platewhich was 5mm thick The ratio of pearlite area to totalsurface area 119875

119903

was controlled by changing heat treatmentprocess as shown in Figure 2 The cast irons were composedof pearlitic matrix ferritic matrix and graphite particles 119875

119903

and the ratio of the graphite particles area to total surface area119866119903

were defined respectively

119875119903

=Area of pearlitic matrixTotal surface area

(1)

119866119903

=Area of graphite particlesTotal Surface area

(2)

Pearlitic matrix is a lamellar mixture of ferrite and cementiteIf it is assumed that the area of ferrite in pearlitic matrix is aslarge as that of cementite the ratio of the ferrite area to totalsurface area 119865

119903

is expressed by

119865119903

= 1 minus 119866119903

minus119875119903

2 (3)

119865119903

decreases from 079 to 054 with increasing 119875119903

from0 to 057 as shown in Table 2 while 119866

119903

does not changeThe average diameter of graphite particles in all specimenswas approximately 20 120583m Figure 3 shows microscopic pho-tographs of specimens

The cast iron of 1 cm2 was grinded with a 1000 grit siliconcarbide (SiC) paper degreased with acetone etched in 1MH2

SO4

solution for 5 seconds at 323K rinsed with distilledwater and dried in air

22 Test Solutions Sulfuric acid solutions at pH = 10 20and 30were preparedThose test solutions containedNa

2

SO4

as a supporting electrolyte so as to keep ionic strength at05mol dmminus3 The test solutions were deaerated with pure

Spec

imen

80

5 3 2225

160 mm

Figure 1 Sand mold and clipping position of specimens

Tem

pera

ture

(K)

1400

1200

1000

800

600

400

200

00 20 40 60

times 104Time (s)

Specimen no in Table 212

34As cast

Figure 2 Heat treatment processes of specimens

nitrogen and agitated with a stirring bar The rotating speedof the stirring bar did not affect the anodic current densities

23 Measurements The specimen was set in an empty cellPure nitrogen was passed through the cell for 3600 secondsThe specimen was not exposed to the air after it was setin the cell The test solution deaerated with pure nitrogenin a reservoir was introduced to the cell The corrosionpotential was measured for 600 seconds after the specimenwas exposed to the test solution Subsequently the linearpotential sweep from the corrosion potential started The

International Journal of Corrosion 3

200120583m

Specimen no 1 (Pr = 0)

(a)

200120583m

No 2 (Pr = 008)

(b)

200120583m

No 3 (Pr = 029)

(c)

200120583m

No 4 (Pr = 057)

(d)

Figure 3 Microscopic photographs of the specimens

sweep rate was ranged from 0005 to 01 V sminus1 A new testpiece was used for each measurement The counter electrodewas platinum A KCl saturated Ag-AgCl reference electrodewas used The solution resistance between the specimenand the reference electrode was measured by ac impedancemethod with a frequency of 2 kHz and an amplitude of0010V The electrode potential was expressed on the SHEscale after the correction of the ohmic potential drop Allelectrochemical measurements were performed at 298KAreas of cementite and graphite particles are assumed notto take part in the anodic dissolution The anodic currentdensity was calculated from

119894119886

=119868119886

119860 sdot 119865119903

(4)

where 119894119886

is the anodic current density 119868119886

is the observedanodic current and 119860 is the total surface area

3 Results and Discussion

31 Anodic Current Density due to Dissolution of Cast IronThe steady-state anodic current can be measured when thesweep rate is lower than 01 V sminus1 Figure 4 shows the anodicpolarization curves of the specimen no 3 in a sulfuric acidsolution at pH = 20 The anodic current densities do notdepend on the sweep rates in the range of 0005 to 01 V sminus1

1

10minus1

10minus2

10minus3

10minus4

minus040 minus035 minus030 minus025 minus020

E versus SHE (V)

i a(A

cmminus2)

Figure 4 Anodic polarization curves of the specimen no 3 in asulfuric acid solution at pH = 20 with a variety of potential sweeprates (I) 01 V sminus1 (998771) 005V sminus1 (◻) 001 V sminus1 and (∙) 0005V sminus1

The sweep rates in this range do not affect the polarizationcurves at other pHs


1

10minus1

10minus2

10minus3

10minus4

10minus5

minus045 minus035 minus025 minus015

E versus SHE (V)

pH = 20pH = 30

pH = 10

i a(A

cmminus2)

Anodic Tafel slope = 0043V decademinus1

Figure 5 Anodic polarization curves of the specimen no 3 insulfuric acid solutions at pH= 10 20 and 30 with a potential sweeprate of 001 V sminus1

Figure 5 illustrates the steady-state anodic polarizationcurves of the specimen no 3 at pHs 10 to 30 with apotential sweep rate of 001 V sminus1 Each curve has a Tafelregion covering more than one decade The anodic Tafelslopes are 0043V decademinus1

It is clear that the anodic current density due to thedissolution of the cast iron at a constant electrode potentialdepends on pH as shown in Figure 5 The anodic currentdensity is expressed by (5) in which the reaction order 119899 willbe discussed in Section 33 Consider

119894119886

= 119896119886

sdot (119886119904

OHminus)119899

sdot exp(23119864

0043) (5)

where 119896119886

is the rate constant of the anodic reaction 119886119904OHminus isthe hydroxyl ion activity at the electrode surface and 119864 is theelectrode potential

The anodic dissolution reaction is controlled by surfacereaction process because convective conditions do not affectpolarization curvesTherefore the hydroxyl ion activity at theelectrode surface is the same as that in the bulk solution TheTafel slope of 0043V decademinus1 in (5) is very close to (23) sdot

(23119877119879119865) The anodic current density 119894119886

of the cast iron canbe expressed by

119894119886

= 119896119886

sdot (119886lowast

OHminus)119899

sdot exp(3119865119864

2119877119879) (6)

where 119886lowast

OHminus is the hydroxyl ion activity in the bulk solution119865 is the Faraday constant 119877 is the gas constant and 119879 is theabsolute temperature

32 Effect of the Ratio of the Pearlite Area on the AnodicCurrent Density A relation of the ratio of the pearlite area119875119903

to the anodic current density 119894119886

is discussed Figure 6shows the plots of log 119894

119886

against 119875119903

at a few constant electrodepotentials and pHs The effect of 119875

119903

on the anodic current

1

10minus1

10minus2

10minus3

0 020 040 060 080Pr

i a(A

cmminus2)

pHEVMarksminus022

minus030

minus037

10

2030

Figure 6 Anodic current densities as a function of the ratio of thepearlite area 119875

119903

at a few constant electrode potentials and pHs

density is not observed This means that the acceleration ofanodic dissolution at interfaces between ferrite and cementitecan be negligible

33 Determination of the Reaction Order with respect to theHydroxyl Ion Activity Three approaches for determining thereaction order with respect to the hydroxyl ion activity areexamined

331 First Approach The reaction order 119899 is given by par-tially differentiating log 119894

119886

with respect to pH in (6) Consider

119899 = (120597 log 119894

119886

120597pH)

119864

(7)

Figure 7 shows the plots of log 119894119886

against pH for anyspecimens nos from 1 to 4 at 119864 = minus030V As the figureshows a straight line with a slope of 1 is obtained

332 Second Approach The partial differentiation of 119864 withrespect to pH is expressed by

(120597119864

120597pH)

119894

119886

= minus(2119899

3) (

23119877119879

119865) (8)

Equation (8) presents that the electrode potential at a con-stant anodic current density is a linear function of pH If 119899 = 1

in (8) the value of the right side is equal to minus0040VpHminus1at 298KThe relationships between the electrode potential at


1

10minus1

10minus2

10minus3

10minus4

10minus5

0 10 20 30 40

i a(A

cmminus2)

pH

Slope = 1

Figure 7 Effect of pH on the anodic current density in sulfuric acidsolutions at 119864 = minus030VThe ratio of pearlite area 119875

119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

minus020

minus025

minus030

minus035

minus0400 10 20 30 40

Eve

rsus

SH

E (V

)

pH

Slope = minus004V pHminus1

Figure 8 Plots of 119864 against pH in sulfuric acid solutions at 119894119886

=

001A cmminus2 The ratio of pearlite area 119875119903

(∙) 0 (◻) 008 (998771) 029and (I) 057

119894119886

= 001A cmminus2 and pH for any specimens are shown inFigure 8 The straight line with a slope of minus0040VpHminus1 isdrawn

333 Third Approach The effect of pH on the corrosionpotential is discussed The anodic current and the cathodiccurrent are equal at the corrosion potential Bockris et al and

minus025

minus030

minus035

minus040

minus0450 10 20 30 40

Eco

rrve

rsus

SH

E (V

)

pH


Figure 9 Relation between the corrosion potential 119864corr and pH insulfuric acid solutions The ratio of pearlite area 119875

119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

Kelly have revealed that the cathodic current density of pureiron is as follows [15 16]

119894119888

= 119896119888

sdot 119886lowast

H+ sdot exp (minus119865119864

2119877119879) (9)

where 119894119888

is the cathodic current density and 119896119888

is the rateconstant of the cathodic reaction The present authors haveconfirmed that the cathodic current density of spheroidalgraphite cast iron is also given by (9) The cathodic currentis the product of 119894

119888

and total surface area The anodic currentis calculated by (4) and (6) The corrosion potential isrepresented in (10) by combining (4) (6) and (9) Consider

119864corr =23119877119879

2119865log

119896119888

119865119903

sdot 119896119886

sdot 119896119908

119899

minus (119899 + 1) sdot pH (10)

where 119864corr is the corrosion potential and 119896119908

is ionizationconstant of waterTherefore the effect of pH on the corrosionpotential is given by

(120597119864corr120597pH

) = minus (119899 + 1) (23119877119879

2119865) (11)

By assuming that 119899 = 1 the value of the right side in (11) isequal to minus0060VpHminus1 at 298K Figure 9 shows the plots of119864corr versus pH for any specimens of nos 1 to 4 The linearrelation between 119864corr and pH is confirmed as shown in thefigure The observed slope is precisely minus0060VpHminus1

It is proved that the three approaches reach the sameresult of 119899 = 1

34 Mechanism of Anodic Dissolution Reaction of Cast IronThemechanisms of iron dissolution reaction in acid solutions


Table 3 Kinetic parameters of typical mechanisms for iron dissolu-tion reaction

Pieces of literature 119887119886

119899

Heusler et al [18ndash20] (12) sdot (23119877119879119865) 2Bockris et al [15] (23) sdot (23119877119879119865) 1Abdul Azim and Sanad [37] 23119877119879119865 1Note 119887

119886

is the anodic Tafel slope and 119899 is the reaction order with respect tothe hydroxyl ion activity

have been proposed by many researchers [15ndash37]The kineticparameters of typicalmechanisms are summarized inTable 3In the mechanism by Bonhoeffer and Heusler the anodicTafel slope is 0030V decademinus1 at 298K and the reactionorder with respect to the hydroxyl ion activity is 2 [18ndash20]According to Bockris et al the anodic dissolution reaction ischaracterized by the anodic Tafel slope of 0040V decademinus1at 298K and the first order dependency on the hydroxylion activity [15] Abdul Azim and Sanad reported that theanodic Tafel slope was 0060V decademinus1 at 298K and thereaction order with respect to the hydroxyl ion activity was 1[37] These results refer to different experimental conditionsLorenz et al studied the effect of heat treatment of iron on theanodic dissolution rate [21 38] They found that the anodicTafel slope was 0030V decademinus1 when the specimen wasannealed at a temperature lower than 673KThe anodic Tafelslope was 0040V decademinus1 for the specimen annealed at atemperature higher than 1023K

In the present study the specimens experienced heattreatment at 993K and 1173 K to change the pearlite areaTheiron wire electrodes used in the Bockris study were heatedin a furnace for 15 minutes at temperatures between 873 and1173 K before electrochemical measurements The Tafel slopeof 0040V decademinus1 obtained by the present authorsrsquo andBockrisrsquo experiments substantiates the findings by Lorenz etal The authorsrsquo results support the following mechanism ofthe anodic dissolution of iron proposed by Bockris et al [15]Consider

Fe + OHminus = (FeOH)ads + e (12)

(FeOH)ads 997888rarr (FeOH)+

+ e [rate determining] (13)

(FeOH)+

= Fe2+ + OHminus (14)

The anodic current density is expressed from the plots inFigures 5 to 8 as follows

log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)

For pure iron Kelly has revealed that the rate equation of theanodic dissolution of iron is as follows [16]

log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)

The anodic current density of the cast iron is higher thanthat of the pure iron Alloyed sulfur and phosphorus tendto promote the anodic reaction even if the content of these

elements is lower than 002 [11 39] The cast iron in thepresent study contains 001 sulfur and 0013 phosphorusThe anodic current density of the cast iron is considered to bestimulated by these elements

4 Conclusions

The anodic dissolution of spheroidal graphite cast iron withdifferent pearlite areas in sulfuric acid solutions is studiedThe main results are as follows

(1) The anodic current density of cast iron is expressed by

119894119886

= 119896119886

sdot 119886lowast

OHminus sdot exp(3119865119864

2119877119879) (17)

which is consistent with that of pure iron proposed byBockris et al

(2) The anodic current density does not depend on thearea of pearliteThe acceleration of anodic dissolutionat interfaces between ferrite and cementite can benegligible

(3) No difference in anodic dissolution reaction mecha-nisms between pure iron and spheroidal graphite castiron is found

References

[1] M Paris and B Bruniere ldquoThe corrosion resistance of ductileiron in sea water and petroleum tanker servicesrdquoCorrosion vol13 no 5 pp 292ndash296 1957

[2] F L Laque ldquoThe corrosion resistance of ductile ironrdquoCorrosionvol 14 no 10 pp 485ndash492 1958

[3] B McEnaney and D C Smith ldquoCorrosion of a cast iron boilerin a model central heating systemrdquo Corrosion Science vol 18no 7 pp 591ndash603 1978

[4] D C Smith and B McEnaney ldquoThe influence of dissolvedoxygen concentration on the corrosion of grey cast iron inwaterat 50∘Crdquo Corrosion Science vol 19 no 6 pp 379ndash394 1979

[5] B McEnaney and D C Smith ldquoThe reductive dissolution of 120574-FeOOH in corrosion scales formed on cast iron in near-neutralwatersrdquo Corrosion Science vol 20 no 7 pp 873ndash886 1980

[6] L M Al-Shama J M Saleh and N A Hikmat ldquoPotentiostaticstudies of the corrosion of grey cast iron in sulphuric acid andsodium hydroxide solutionsrdquo Corrosion Science vol 27 no 3pp 221ndash228 1987

[7] R Mehra and A Soni ldquoCast iron deterioration with time invarious aqueous salt solutionsrdquoBulletin ofMaterials Science vol25 no 1 pp 53ndash58 2002

[8] A Reynaud ldquoCorrosion of cast ironsrdquo in Shreirrsquos Corrosion TJ A Richardson Ed vol 3 Chapter 2 pp 1737ndash1788 ElsevierAmsterdam The Netherlands 2010

[9] MG FontanaCorrosion Engineering McGraw-Hill NewYorkNY USA 1987

[10] KHorikawa S Takiguchi Y Ishizu andMKanazashi ldquoStudieson the atmospheric corrosion of metals and anti-corrosivecoatings in Japan (5th Report)rdquo Boushoku-Gijutsu[CorrosionEngineering of Japan] vol 16 no 4 pp 153ndash158 1967

[11] H H Uhlig Corrosion and Corrosion Control John Wiley ampSons New York NY USA 1963


[12] K Nakamura and H Sumimoto ldquoRelationship betweenmicrostructure and stress-strain curve of grey cast ironrdquo Imonovol 39 no 6 pp 480ndash493 1967

[13] K R Trethewey and J Chamberlain Corrosion for Science andEngineering Longman GBR Essex UK 1995

[14] U R Evans The Corrosion and Oxidation of Metals ScientificPrinciples and Practical Applications Edward Arnold GBRLondon UK 1960

[15] J OrsquoM Bockris D Drazic and A R Despic ldquoThe electrodekinetics of the deposition and dissolution of ironrdquo Electrochim-ica Acta vol 4 no 2ndash4 pp 325ndash361 1961

[16] E J Kelly ldquoThe active iron electrode I Iron dissolutionand hydrogen evolution reactions in acidic sulfate solutionsrdquoJournal of the Electrochemical Society vol 112 no 2 pp 124ndash1311965

[17] A J Bard Encyclopedia of Electrochemistry of the ElementsMarcel Dekker New York NY USA 1982

[18] K F Bonhoeffer and K E Heusler ldquoAbhangigkeit der anodis-chen Eisenauflosung von der Saurekonzentrationrdquo ZeitschriftFur Physikalische Chemie vol 8 pp 390ndash393 1956

[19] K F Bonhoeffer and K E Heusler ldquoBemerkung uber dieanodische Auflosung von Eisenrdquo Zeitschrift Fur ElektrochemieBerichte der Bunsengesellschaft Fur Physikalische Chemie vol 61no 1 pp 122ndash123 1957

[20] K E Heusler ldquoDer Einfluszlig der Wasserstoffionenkonzentrationauf das electrochemische Verhaiten des aktiven Eisens insauren Losungenrdquo Zeitschrift Fur Elektrochemie Berichte derBunsengesellschaft Fur Physikalische Chemie vol 62 no 5 pp582ndash587 1958

[21] G Eichkorn W J Lorenz L Albert and H Fischer ldquoEinfluszligder oberflachenaktivitat auf die anodischen auflosungsmech-anismen von eisen in sauren losungenrdquoElectrochimicaActa vol13 no 2 pp 183ndash197 1968

[22] T Hurlen ldquoElectrochemical behaviour of ironrdquo Acta ChemicaScandinavica vol 14 pp 1533ndash1554 1960

[23] K E Heusler and G H Cartledge ldquoThe influence of iodide ionsand carbon monoxide on the anodic dissolution of active ironrdquoJournal of the Electrochemical Society vol 108 no 8 pp 732ndash740 1961

[24] W J Lorenz H Yamaoka and H Fischer ldquoZum electrochemis-chen Verhalten des Eisens in salzsauren Losungenrdquo Berichte derBunsengesellschaft Fur Physikalische Chemie vol 67 no 9-10pp 932ndash943 1963

[25] W J Lorenz G Eichkorn and CMayer ldquoUber den Einfluszlig vonsulfationen auf die kinetik der anodischen Eisenauflosung insauren losungenrdquo Corrosion Science vol 7 no 6 pp 357ndash3651967

[26] R M Shemenski F H Beck and M G Fontana ldquoDissolutionkinetics and polarization of iron whiskersrdquo Corrosion vol 21no 2 pp 39ndash47 1965

[27] C Voigt ldquoBeitrag zur kinetik der korrosion von Fe in saurensulfat- und perchloratlosungenrdquoElectrochimica Acta vol 13 no10 pp 2037ndash2050 1968

[28] J OrsquoM Bockris andHKita ldquoAnalysis of galvanostatic transientsand application to the iron electrode reactionrdquo Journal of theElectrochemical Society vol 108 no 8 pp 676ndash685 1961

[29] J OrsquoM Bockris and D Drazic ldquoThe kinetics of deposition anddissolution of iron effect of alloying impuritiesrdquo ElectrochimicaActa vol 7 no 3 pp 293ndash313 1962

[30] T P Hoar and R D Holliday ldquoThe inhibition by quinolines andthioureas of the acid dissolution ofmild steelrdquo Journal of AppliedChemistry vol 3 no 11 pp 502ndash513 1953

[31] A C Makrides N M Komodromos and N HackermanldquoDissolution of metals in aqueous acid solutionsrdquo Journal of theElectrochemical Society vol 102 pp 363ndash369 1955

[32] A C Makrides ldquoDissolution of iron in sulfuric acid and ferricsulfate solutionsrdquo Journal of the Electrochemical Society vol 107no 11 pp 869ndash877 1960

[33] M Stern and R M Roth ldquoAnodic behavior of iron in acidsolutionsrdquo Journal of the Electrochemical Society vol 104 no 6pp 390ndash392 1957

[34] L Felloni ldquoThe effect of pH on the electrochemicalbehaviourof iron in hydrochloric acidrdquo Corrosion Science vol 8 no 3 pp133ndash148 1968

[35] G J Bignold and M Fleischmann ldquoIdentification of transientphenomena during the anodic polarisation of iron in dilutesulphuric acidrdquo Electrochimica Acta vol 19 no 7 pp 363ndash3741974

[36] G Okamota M Nagayama and N Sato ldquoApplication of therapid method for the measurement of polarization characteris-tics of iron in acid solutionsrdquo in Proceedings of the 8thMeeting ofthe International Committee of Electrochemical Thermodynam-ics and Kinetics (C I T C E) pp 72ndash89 1956

[37] A A Abdul Azim and S H Sanad ldquoThe anodic dissolution ofFe and C-steel in acidic sulphate solutionrdquo Electrochimica Actavol 17 no 9 pp 1699ndash1704 1972

[38] W J Lorenz and G Eichkorn ldquoEinfluszlig des Subgefuges aufden Mechanismus der anodischen Eisenauflosung in saurenLosungenrdquo Berichte der Bunsengesellschaft fur PhysikalischeChemie vol 70 no 1 pp 99ndash106 1966

[39] M Stern ldquoThe effect of alloying elements in iron on hydrogenover-voltage and corrosion rate in acid environmentsrdquo Journalof the Electrochemical Society vol 102 no 12 pp 663ndash668 1955

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Table 1 Chemical composition of the spheroidal graphite cast iron(mass)

C Si Mn P S Cu Mg367 199 041 0013 001 019 0046

Table 2 Ratios of the pearlite area the graphite particles area andthe ferrite area

Specimen no 119875119903

119866119903

119865119903

(1) (2) (3)1 0 021 0792 008 019 0773 029 020 0654 057 018 054The ratios of the pearlite area 119875

119903

the graphite particles area 119866119903

and theferrite area 119865

119903

are defined by (1) (2) and (3) respectively

2 Experimental

21 Specimen The chemical composition of specimens ofspheroidal graphite cast iron (hereinafter referred to as castiron) is given in Table 1 Cast irons which have different areasof pearlite were prepared A sand mold given in Figure 1was used for casting Specimens were clipped from the platewhich was 5mm thick The ratio of pearlite area to totalsurface area 119875

119903

was controlled by changing heat treatmentprocess as shown in Figure 2 The cast irons were composedof pearlitic matrix ferritic matrix and graphite particles 119875

119903

and the ratio of the graphite particles area to total surface area119866119903

were defined respectively

119875119903

=Area of pearlitic matrixTotal surface area

(1)

119866119903

=Area of graphite particlesTotal Surface area

(2)

Pearlitic matrix is a lamellar mixture of ferrite and cementiteIf it is assumed that the area of ferrite in pearlitic matrix is aslarge as that of cementite the ratio of the ferrite area to totalsurface area 119865

119903

is expressed by

119865119903

= 1 minus 119866119903

minus119875119903

2 (3)

119865119903

decreases from 079 to 054 with increasing 119875119903

from0 to 057 as shown in Table 2 while 119866

119903

does not changeThe average diameter of graphite particles in all specimenswas approximately 20 120583m Figure 3 shows microscopic pho-tographs of specimens

The cast iron of 1 cm2 was grinded with a 1000 grit siliconcarbide (SiC) paper degreased with acetone etched in 1MH2

SO4

solution for 5 seconds at 323K rinsed with distilledwater and dried in air

22 Test Solutions Sulfuric acid solutions at pH = 10 20and 30were preparedThose test solutions containedNa

2

SO4

as a supporting electrolyte so as to keep ionic strength at05mol dmminus3 The test solutions were deaerated with pure

Spec

imen

80

5 3 2225

160 mm

Figure 1 Sand mold and clipping position of specimens

Tem

pera

ture

(K)

1400

1200

1000

800

600

400

200

00 20 40 60

times 104Time (s)

Specimen no in Table 212

34As cast

Figure 2 Heat treatment processes of specimens

nitrogen and agitated with a stirring bar The rotating speedof the stirring bar did not affect the anodic current densities

23 Measurements The specimen was set in an empty cellPure nitrogen was passed through the cell for 3600 secondsThe specimen was not exposed to the air after it was setin the cell The test solution deaerated with pure nitrogenin a reservoir was introduced to the cell The corrosionpotential was measured for 600 seconds after the specimenwas exposed to the test solution Subsequently the linearpotential sweep from the corrosion potential started The


200120583m


(a)

200120583m

No 2 (Pr = 008)

(b)

200120583m

No 3 (Pr = 029)

(c)

200120583m

No 4 (Pr = 057)

(d)



119894119886

=119868119886

119860 sdot 119865119903

(4)

where 119894119886





1

10minus1

10minus2

10minus3

10minus4


E versus SHE (V)

i a(A

cmminus2)




1

10minus1

10minus2

10minus3

10minus4

10minus5


E versus SHE (V)

pH = 20pH = 30

pH = 10

i a(A

cmminus2)





119894119886

= 119896119886

sdot (119886119904

OHminus)119899

sdot exp(23119864

0043) (5)

where 119896119886





119894119886

= 119896119886

sdot (119886lowast

OHminus)119899

sdot exp(3119865119864

2119877119879) (6)

where 119886lowast





119886

against 119875119903


119903


1

10minus1

10minus2

10minus3

0 020 040 060 080Pr

i a(A

cmminus2)

pHEVMarksminus022

minus030

minus037

10

2030


119903





119886


119899 = (120597 log 119894

119886

120597pH)

119864

(7)




(120597119864

120597pH)

119894

119886

= minus(2119899

3) (

23119877119879

119865) (8)




1

10minus1

10minus2

10minus3

10minus4

10minus5

0 10 20 30 40

i a(A

cmminus2)

pH

Slope = 1


119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

minus020

minus025

minus030

minus035

minus0400 10 20 30 40

Eve

rsus

SH

E (V

)

pH



=


(∙) 0 (◻) 008 (998771) 029and (I) 057

119894119886



minus025

minus030

minus035

minus040

minus0450 10 20 30 40

Eco

rrve

rsus

SH

E (V

)

pH



119903

(∙) 0 (◻) 008(998771) 029 and (I) 057


119894119888

= 119896119888

sdot 119886lowast


2119877119879) (9)

where 119894119888



119888


119864corr =23119877119879

2119865log

119896119888

119865119903

sdot 119896119886

sdot 119896119908

119899

minus (119899 + 1) sdot pH (10)



(120597119864corr120597pH

) = minus (119899 + 1) (23119877119879

2119865) (11)







119899


119886







(FeOH)+



log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)


log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)



4 Conclusions



119894119886

= 119896119886

sdot 119886lowast


2119877119879) (17)




References
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




200120583m


(a)

200120583m

No 2 (Pr = 008)

(b)

200120583m

No 3 (Pr = 029)

(c)

200120583m

No 4 (Pr = 057)

(d)



119894119886

=119868119886

119860 sdot 119865119903

(4)

where 119894119886





1

10minus1

10minus2

10minus3

10minus4


E versus SHE (V)

i a(A

cmminus2)




1

10minus1

10minus2

10minus3

10minus4

10minus5


E versus SHE (V)

pH = 20pH = 30

pH = 10

i a(A

cmminus2)





119894119886

= 119896119886

sdot (119886119904

OHminus)119899

sdot exp(23119864

0043) (5)

where 119896119886





119894119886

= 119896119886

sdot (119886lowast

OHminus)119899

sdot exp(3119865119864

2119877119879) (6)

where 119886lowast





119886

against 119875119903


119903


1

10minus1

10minus2

10minus3

0 020 040 060 080Pr

i a(A

cmminus2)

pHEVMarksminus022

minus030

minus037

10

2030


119903





119886


119899 = (120597 log 119894

119886

120597pH)

119864

(7)




(120597119864

120597pH)

119894

119886

= minus(2119899

3) (

23119877119879

119865) (8)




1

10minus1

10minus2

10minus3

10minus4

10minus5

0 10 20 30 40

i a(A

cmminus2)

pH

Slope = 1


119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

minus020

minus025

minus030

minus035

minus0400 10 20 30 40

Eve

rsus

SH

E (V

)

pH



=


(∙) 0 (◻) 008 (998771) 029and (I) 057

119894119886



minus025

minus030

minus035

minus040

minus0450 10 20 30 40

Eco

rrve

rsus

SH

E (V

)

pH



119903

(∙) 0 (◻) 008(998771) 029 and (I) 057


119894119888

= 119896119888

sdot 119886lowast


2119877119879) (9)

where 119894119888



119888


119864corr =23119877119879

2119865log

119896119888

119865119903

sdot 119896119886

sdot 119896119908

119899

minus (119899 + 1) sdot pH (10)



(120597119864corr120597pH

) = minus (119899 + 1) (23119877119879

2119865) (11)







119899


119886







(FeOH)+



log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)


log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)



4 Conclusions



119894119886

= 119896119886

sdot 119886lowast


2119877119879) (17)




References
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1

10minus1

10minus2

10minus3

10minus4

10minus5


E versus SHE (V)

pH = 20pH = 30

pH = 10

i a(A

cmminus2)





119894119886

= 119896119886

sdot (119886119904

OHminus)119899

sdot exp(23119864

0043) (5)

where 119896119886





119894119886

= 119896119886

sdot (119886lowast

OHminus)119899

sdot exp(3119865119864

2119877119879) (6)

where 119886lowast





119886

against 119875119903


119903


1

10minus1

10minus2

10minus3

0 020 040 060 080Pr

i a(A

cmminus2)

pHEVMarksminus022

minus030

minus037

10

2030


119903





119886


119899 = (120597 log 119894

119886

120597pH)

119864

(7)




(120597119864

120597pH)

119894

119886

= minus(2119899

3) (

23119877119879

119865) (8)




1

10minus1

10minus2

10minus3

10minus4

10minus5

0 10 20 30 40

i a(A

cmminus2)

pH

Slope = 1


119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

minus020

minus025

minus030

minus035

minus0400 10 20 30 40

Eve

rsus

SH

E (V

)

pH



=


(∙) 0 (◻) 008 (998771) 029and (I) 057

119894119886



minus025

minus030

minus035

minus040

minus0450 10 20 30 40

Eco

rrve

rsus

SH

E (V

)

pH



119903

(∙) 0 (◻) 008(998771) 029 and (I) 057


119894119888

= 119896119888

sdot 119886lowast


2119877119879) (9)

where 119894119888



119888


119864corr =23119877119879

2119865log

119896119888

119865119903

sdot 119896119886

sdot 119896119908

119899

minus (119899 + 1) sdot pH (10)



(120597119864corr120597pH

) = minus (119899 + 1) (23119877119879

2119865) (11)







119899


119886







(FeOH)+



log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)


log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)



4 Conclusions



119894119886

= 119896119886

sdot 119886lowast


2119877119879) (17)




References
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1

10minus1

10minus2

10minus3

10minus4

10minus5

0 10 20 30 40

i a(A

cmminus2)

pH

Slope = 1


119903

(∙) 0 (◻) 008(998771) 029 and (I) 057

minus020

minus025

minus030

minus035

minus0400 10 20 30 40

Eve

rsus

SH

E (V

)

pH



=


(∙) 0 (◻) 008 (998771) 029and (I) 057

119894119886



minus025

minus030

minus035

minus040

minus0450 10 20 30 40

Eco

rrve

rsus

SH

E (V

)

pH



119903

(∙) 0 (◻) 008(998771) 029 and (I) 057


119894119888

= 119896119888

sdot 119886lowast


2119877119879) (9)

where 119894119888



119888


119864corr =23119877119879

2119865log

119896119888

119865119903

sdot 119896119886

sdot 119896119908

119899

minus (119899 + 1) sdot pH (10)



(120597119864corr120597pH

) = minus (119899 + 1) (23119877119879

2119865) (11)







119899


119886







(FeOH)+



log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)


log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)



4 Conclusions



119894119886

= 119896119886

sdot 119886lowast


2119877119879) (17)




References
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119899


119886







(FeOH)+



log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + (35 plusmn 03) (15)


log 119894119886

=3119865119864

23 sdot 2119877119879+ pH + 26 (16)



4 Conclusions



119894119886

= 119896119886

sdot 119886lowast


2119877119879) (17)




References
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Anodic Dissolution of Spheroidal Graphite Cast … · 2019. 7. 31. ·...

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Transcript of Research Article Anodic Dissolution of Spheroidal Graphite Cast … · 2019. 7. 31. ·...