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Passivation Behaviors of Super Martensitic Stainless Steel in Weak Acidic and Weak Alkaline NaCl Solutions
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( １ ２):１ １ ５ ６ Ｇ １ １ ６ ３
Pa s s i v a t i onBe ha v i o r so fSupe rMa r t e n s i t i cS t a i n l e s sS t e e li n We akAc i d i cand We akAl ka l i neNaC lSo l u t i on s １ １ J i anKANG１ , JunLI１ , Kun Ｇ Ｇ l ong YONG２ , J i eSU２ yuZHAO , XuanBAI , Qi
( １． I ns t i t u t eo fMa t e r i a l sSc i enc eandEng i ne e r i ng,Kunmi ngUn i ve r s i t fSc i enc eandTe chno l ogy,Kunmi ng６５００９３, yo Yunnan,Ch i na; ２． I ns t i t u t eo fS t r uc t u r a lMa t e r i a l s,Ce n t r a lI r ona ndS t e e lRe s e a r c hI n s t i t u t e,Be i i ng１０００８１,Ch i n a) j Ab s t r a c t:Thepa s s i va t i onbehav i o r so fsupe rma r t ens i t i cs t a i n l e s ss t e e l s( SMSS)we r es t ud i edbypo l a r i z a t i oncu r ve s a tpa s s i vepo t en t i a lo f－０ １Vandi nva r i ousNaCls o l u t i ons,e l e c t r o chemi c a limpedanc espe c t r o s c opy ( EI S)andXＧ r aypho t oe l e c t r onspe c t r o s c opy ( XPS)ana l s i s．El e c t r o chemi c a lt e s tr e su l t sshowedt ha t,i na l ka l i nes o l u t i ons,pa s Ｇ y s i va t i onr eg i onwi d t hwa swi de r,pa s s i va t i oncu r r en twa ssma l l e r,andpo l a r i z a t i onr e s i s t anc ewa sg r e a t e r;t hus,t he s s i vef i lmo fSMSSi na l ka l i nes o l u t i onshadbe t t e rpa s s i va t i onbehav i o r st hant ha ti na c i d i cs o l u t i ons．Thepo l a r i z a Ｇ pa t i oncu r veandEI So fs amp l e sSMSS１andSMSS２ we r ea l s ous edt os t udywh i chs amp l ehadbe t t e rpa s s i va t i onbe Ｇ hav i o r s．Al lr e su l t sdemons t r a t edt ha tpa s s i vef i lms t r uc t u r eo fSMSS１s amp l ewa smo r es t ab l e,andc apa c i t fpa s Ｇ yo s i vef i lm wa senhanc ed．Theimpa c to fa l l oy i nge l emen t sont hepa s s i vef i lm ( SMSS)pa s s i va t i onc apab i l i t sa l s o ywa d i s cus s edbyXPSdep t hp r o f i l i ng,and XPSdep t hp r o f i l i ngshowedt ha tt hec ompo s i t i ono ft hepa s s i vef i lm wa s ma i n l ompo s edo fFe Ｇ ox i deandCr Ｇ ox i de． Sot hepa s s i vef i lms t r uc t u r e swe r emi xedl aye r so fFe Ｇ ox i deandCr Ｇ ox Ｇ yc i de．Feox i da t i onp r oduc tandCrox i da t i onp r oduc twou l dhe l oimp r ovet hep r o t e c t i vep r ope r t fpa s s i vef i lm, pt yo wh i chc ou l dp r omo t et hef o rma t i ono fapa s s i vef i lms t r uc t u r emo r es t ab l e l yanddens y． Ke r d s:supe rma r t ens i t i cs t a i n l e s ss t e e l;pHva l ue;po l a r i z a t i oncu r ve;e l e c t r o chemi c a limpedanc espe c t r o s c opy; ywo XPSdep t hp r o f i l i ng
Supe rma r t ens i t i cs t a i n l e s ss t e e l s( SMSS)wi t h , chan i c a lpr ope r t i e sc o r r o s i onr e s i s t anc eand goodme we l dab i l i t enwi de l l i edi nt hewo r l da s yhavebe yapp a l t e rna t i ve ma t e r i a l st odup l exs t a i n l e s ss t e e l sand c a rbons t e e l,e spe c i a l l no f f sho r ep i l i ne sandt he yi pe o i landga si ndus t r o rc o r r o s i onr e s i s t anc et oCO２ yf and H２S．Co r r o s i onr e s i s t anc eo fs t a i n l e s ss t e e li s c l o s e l e l a t edt ot hec ompo s i t i onandp r ope r t i e so f yr t he pa s s i vef i lm,such a st he s t ab i l i t i t y,dens y, c ompos i t i on and s t ruc t u r e．Gene r a l l he pa s s i ve y,t f i lm o fs t a i n l e s ss t e e lwa sc ompo s edo ftwo pa r t s: t hei nne rl aye rc on t a i n i ngchr omi um ox i de wa st he ; ma i npa r to ft hepa s s i vef i lma saba r r i e rl aye rt he ou t e rl aye rwa s ma i n l ompo s edo fi r onox i deand yc [ ,] hyd r ox i de１ ２ ．Bu tt hepa s s i vef i lm maychangewi t h t hea l l oycompo s i t i on,po t en t i a lo rt hee l e c t r o l t e, y e spe c i a l l o rpHva l ue． yf Theadd i t i ono fmo l r omo t e st heFe Ｇ ybdenum p
ox i deandCr Ｇ ox i def o rmed mo r es t ab l hepa s Ｇ yont s i vef i lm．Add i ng mo l b d e n u m t o s t a i n l e s s s t e e l y [ ３ Ｇ ５] cou l dimp r ovet hep i t t i ngco r r os i onr e s i s t anc e ． I t wasma i n l othef ac ttha tMor educ edCl－ i Ｇ yduet onsga t he r i ngont hepa s s i vef i lm．Thepo l a r i z a t i on cur veshowedt ha t Cl－ i ons t r ong l r ovedt he yimp i t t i n s u s c e t i b i l i t a n dh a d l i t t l ee f f e c to n i r o no x Ｇ p g p y [ ６] i def i lmg r owt hi nt hepa s s i ver eg i ons ．W wa susu Ｇ a l l n t ocomme r c i a ls t a i n l e s ss t e e l,andi t s yaddedi con t r i bu t i ont ot hep r ope r t fp i t t i ngco r r os i onr e Ｇ yo [] s i s t anc ewa ss imi l a rt o Mo．Ol s sonand Lando l t７ s t ud i edt hesur f a c ep r ope r t i e so fa l l oycon t a i n i ng Mo and W．Tungs t a t ewa sf o rmedbyt hei n t e r a c t i ono f WO２－ ndc a t i ons．Thei onshadava r i e t fbehav Ｇ yo ４ a i o r si nt heco r r os i on p r oc e s s:comb i n i ng wi t hc a t Ｇ i ons,r educ i ngt he mob i l i t fi ons,o rsupp r e s s i ng yo [] adso r t i ono fCl－ i ons．Kim e ta l ８ f oundt ha tt he p a c t i va t i ngcur r en tdens i t fdup l exs t e e lcon t a i n i ng yo
Founda t i onI t em: I t em Spons o r edbyEduc a t i onDepa r tmen tSc i en t i f i cRe s e a r chFundPr o e c tf r om YunnanPr ov i nc eo fCh i na ( ２０１２Y５４４) j B i o r aphy: J i anKANG,Ma s t e r; E Ｇma i l: n i_j i an＠１２６ c om; Re c e i v e dDa t e:Oc t obe r２９,２０１４ gemi g Co r r e s i ngAu t ho r:JunLI,Do c t o r,Le c t ur e sh i Ｇma i l:l ９８１＠１２６ c om p; E jwj pond
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
W wa ss l i t l a r rt hant ha to fdup l exs t e e lno t gh yl ge c on t a i n i ng W,bu tt hepa s s i va t i oncu r r en tdens i t f yo dup l exs t e e lc on t a i n i ng Wi sl owe r． I na l ka l i nes o l u t i ons,Fe Ｇ ox i del aye rusua l l s yha , ah i hs t a b i l i t ． H o w e v e r t h eC r Ｇ o x i d el a e rh a sa g y y h i rs t ab i l i t na c i d i cs o l u t i ons．Thee f f e c to fpH ghe yi ont hepa s s i vef i lm o fFe ＧCra l l oysha sbe ens t ud i ed [] [ ] byS t r ehb l ow ９ and Hoppe１０ ．Theyf oundt ha tt he f i lm wa sf o rmed mo r es t ab l na l ka l i nes o l u t i ons, yi andt henumbe ro fFe ( I I I)ox i dei nc r e a s eds i i f i Ｇ gn c an t l ． T h er e s e a r c ho fs t e a d Ｇ s t a t eo x i d ef i l m h a d y y showedt ha tat h i nba r r i e rl aye ro fCr Ｇ ox i dec l o s et o t hef i lme l e c t r o l t ei n t e r f a c ewa sf o rmedont hepa s Ｇ y / s i vef i lm unde rpo t e n t i o s t a t i cc ond i t i on si n０ ５ mo lL [ ] H２SO４ １１ ．An i ons( Cl－ o rS２－ ) i nt hes o l u t i ons,e s Ｇ c i a l l na c i d i cs o l u t i ons,hadh i rc apa c i t r Ｇ pe yi ghe ype [ ] me a t i ngt opa s s i vef i lm o fFe ＧCra l l oys１２ ． I na c i d i c med i a,３０４Land３１６Ls t a i n l e s ss t e e l sc ou l dexh i b i t a c t i ve Ｇ s s i vebehav i o rdu r i nganod i cpo l a r i s a t i oni n pa wh i chH２Ss i i f i c an t l nc r e a s e st hec r i t i c a lcu r r en t gn yi [ ] dens i t t ha l l oys１３ ．S t a i n l e s ss t e e l wa sa l s o yon bo us edi n an a l ka l i neenv i r onmen ta st her e i n f o r c ed c onc r e t e．Thes t a i n l e s ss t e e lc ou l dp r o l ongl i f eand r educ et hedamagec aus edbyt heimpa c to fc o r r o Ｇ [ ] s i on１４ ． I nt he s ea l ka l i nec ond i t i ons,ex t r eme l t h i n y r o t e c t i vef i lm wa ss t r ong l r en tandchemi c a l l p yadhe y s t ab l e． I thadah i l r o t e c t i veox i def i lmt ha tc ov Ｇ gh yp [ ] e r st hes t a i n l e s ss t e e lsu r f a c e１５ ． Ac co rd i ngt ot heex i s t i ngr e s e a r che s,t hec o r r o Ｇ s i onr e s i s t anc eo fs t a i n l e s ss t e e l si sr e l a t edt oi t spa s Ｇ s i vep r ope r t tt hes t udyonSMSSpa s s i vep r op Ｇ y．Bu e r t sr a r e l epo r t ed．The r e f o r e,t he pa s s i va t i on yi yr behav i o ro fSMSSi n we aka c i d i cand we aka l ka l i ne , env i r onmen t swa sr e s e a r ched wh i chi so fg r e a ts i Ｇ g n i f i c anc et of u r t he rexp l a i nt hec o r r o s i onr e s i s t anc e [ ] o fSMSS１６ ． I nt h i spape r,t hepa s s i va t i onbehav i o r o fSMSSbypo t en t i odynami cpo l a r i z a t i onandEI Si n ３ ５ ma s s％ NaCls o l u t i onswi t hpHo f４and１０wa s i nve s t i t ed．Comb i n i ng wi t ht he XPSdep t hp r o f i Ｇ ga l i ng,t hema i ne l emen t se f f e c ti nt hepa s s i vef i lm o f SMSSwa sa l s oexp l o r ed．
１ Exp e r imen t a l
Twok i ndso fsupe rma r t ens i t i cs t a i n l e s ss t e e l s SMSS１andSMSS２we r echo s en,andt her a t i oo fe l Ｇ emen t si ns t a i n l e s ss t e e lwa sba s edonex i s t i ngr e Ｇ [ ] s e a r che s１７Ｇ１９ ．Thes amp l e swe r eme l t edi nt heva cu Ｇ umi nduc t i onme l t i ngf u rna c e,andd i r e c t l c a s t i n t o y i ngo t s．Thea c t ua lc ompo s i t i onso fs t e e ls amp l e sa r e showni nTab l e１．Thes amp l e swe r ep r o c e s s edi n t o ８ mm×８ mm×１５ mmby wi r ecu t t i ng．Al ls amp l e s
１１５７
we r ehe a tt r e a t eda sf o l l ows:ho l d i nga t１０５０ ℃ f o r ３０ mi n,t henquench i ng ( o i lquench i ng),andt emＧ r i nghe a tp r e s e r va t i ona t６５０ ℃f o r２h．Thes amＧ pe l e sa f t e rhe a tt r e a tmen twe r epo l i shedby３６０g r i t, p ８００g r i t,１２００g r i t,and３０００g r i twa t e r r o o fs a n d Ｇ p , , r and we l ded wi t hcoppe r wi r e s wa shed by pape
d i s t i l l ed wa t e ra c e t one and e t hano l．Al ls amp l e s we r es e a l edbyepoxyr e s i nandc u r i nga e n t．Samp l e g s u r f a c ea r e ai sabou t０ ５cm２．Theso l u t i onsf o rt he t e s t sa r ed i f f e r en tpH ( ４,１０)３ ５ ma s s％ NaClso Ｇ ( ) l u t i ons con t a i n i ngoxygen ．Al lexpe r imen t s we r e r f o rmeda t( ２０±１)℃． pe T a b l e１ Ch emi c a lc omp o s i t i o n so fe xp e r ime n t a ls t e e l sma s s％ S t e e l
C
Mn
S i
Cr
Ni
Mo
W
Cu
SMSS２ ０ ０２１ ０ ４０ ０ ２７ １４ ８２ ６ ５ １ ８０
０
１ ４５
SMSS１ ０ ０２１ ０ ４０ ０ ２７ １４ ７８ ６ ５ ２ ０４ ０ ８ １ ４４
The me a sur emen tdev i c eo f po t en t i odynami c l a r i z a t i on cur ve and e l e c t r ochemi c a limpedanc e po spe c t r os copyi sFr anc eB i o ＧLog i c ′ sVSP Ｇ ３００e l e c t r o Ｇ , chemi s t r ns t rumen t andt heso f twa r es t em i s yi ys ECＧLabso f twa r e V１０ １８．Al lexpe r imen t sus et he c l a s s i c a lt hr e e Ｇ e l e c t r odes t em:wo rk i ng e l e c t r ode ys (WE),coun t e re l e c t r ode ( CE)andr e f e r enc ee l e c Ｇ t r ode ( REF)wh i chi sas a t ur a t edc a l ome le l e c t r ode ( SCE)．Thepo t en t i odynami cpo l a r i z a t i oncur vewa s me a sur edwi t has c anr a t eo f１ mV/s．Po t en t i os t a t i c l a r i z a t i onpa r ame t e r sbe f o r e EISt e s ta r ea sf o l Ｇ po : l ows t he me a sur edpo t en t i a lwa s －０ １ Vandt he l a r i z a t i ont imewa s１h．TheEISt e s t swe r econ Ｇ po duc t edbyho l d i ngt hes amp l e sa tas e r i e so fspe c i f i ed t en t i a l si nt hef r equenc ang i ngf r om１００kHzt o po yr １ ０mHz,w i t has i a lamp l i t ud ep e r t u r b a t i ono f１ ０mV． gn TheEISp l o t swe r eana l z edbyZv i ewso f twa r e．Al l y expe r imen t swe r emadet hr e et ime st oensur er ep r o Ｇ duc i b i l i t i r s ts t epi na l lt e s t sa r ep r ep r oc e s s Ｇ y．Thef i ngf o r１０mi ni nt hec a t hod i cpo l a r i z a t i onpo t en t i a l, i no rde rt or emove pa s s i ve f i lm o fa l ls amp l e s f o rmedi nt hea i r． XPSt e s tequ i tus e st hePHI５５００ Ve r s a Ｇ pmen Pr obe XＧ r ay pho t oe l e c t r on spe c t r os cope,and t he t t e rnana l i sso f twa r ei st hePHI ＧMu l t i Pakso f t Ｇ pa ys wa r es t ems．XＧ r ay exc i t a t i on sour c ei s Al Kα ys ( １４８６ ６eV),us edi n２４ ５ W wo rk i ngcond i t i ons． ( ) Tak i ngt heb i nd i ngene r fC１ s ２８４ ８eV a san gyo i n t e rna ls t anda rd,t he pe ako ft he me a sur edspe c Ｇ , t rum ha sbe enco r r e c t ed anda l lt hes amp l e s ′sur Ｇ f a c e sa r es t r i t oe l e c t r onspe c t r ome t e r ppedby a pho a rgoni ongunl aye rbyl aye r．
１１５８
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
WO２－ onp r oduc ed８ ．Thei onsc ansupp r e s st head Ｇ ４ i － nt heco r r os i on,r educ i ngt he so rp t i ono fCl i onsi s i b i l i t fp i t t i ng co r r os i on oc cur r enc e．Ont he pos yo o t he rhand,a c co rd i ngt ot het heo r fpo i n t Ｇ de f e c t s, yo []
２ Re s u l t sandDi s c u s s i on ２ １ Po l a r i z a t i onc u r v e sana l s i so fSMSSs amp l e si n y d i f f e r en tpHc ond i t i on s F i １ showst he po l a r i z a t i on cu r ve so ftwo g ( ) k i ndso fs amp l e si na c i d i c pH ４ anda l ka l i ne ( pH １０)c ond i t i ons．Thee l e c t r o chemi c a lpa r ame t e r sc a l Ｇ cu l a t edf r omt hecu r ve sa r el i s t edi nTab l e２． I nt he ３ ５ ma s s％ NaCls o l u t i ons,Ept and Ecorr o fSMSS s amp l e si npH４ ( F i １( a))a r es l i t l e s st h a nt ho s e g gh yl ( ) ) i npH１０ ( F i １ b ． I tc o u l db ec o n s i d e r e dt h a t t h e g e f f e c to f W wa s mo r eobv i oust oSMSS２s amp l e ′s s s i vef i lm wi t hp i t t i ngc o r r o s i on． I twa sduet ot he pa
t hee l e c t r ondono r sdopeda r ema i n l c an Ｇ yoxygenva c i e si nt hef i lm．Andoxygenva c anc i e sc anr e a c twi t h t heso l u t i ono fOH－ i ons,p r omo t i ngt heg r owt ho f [ ２０] , t hepa s s i vef i lm ．The r e f o r e when pH va l ueo f t heso l u t i oni sh i r,t hes t ab i l i t fpa s s i vef i lm ghe yo [ ] wi l lbes t r onge r２０ ． Sot hep i t t i ngpo t en t i a li sh i r ghe , i na l ka l i necond i t i ont hani na c i d i ccond i t i on wh i ch showst ha tt hepa s s i vef i lmf o rmedha ss t r onge rp i t Ｇ t i ngco r r os i onr e s i s t anc ei na l ka l i necond i t i ons．
F i １ Po l a r i z a t i onc u r v e so fSMSS １andSMSS ２i npH４ ( a)andpH１０ ( b)３ ５ma s s％ NaC ls o l u t i on s g Tab l e２ Ma i ne v a l ua t i onpa r ame t e r so fpo l a r i z a t i onc u r v e s Samp l e
Ept/V
Ecorr/V
( /V Ept－Ecorr)
Ip/(mAcm－２)
－０ ２１７９
０ ３０７４
９ ２×１０－３
SMSS１ Ｇ pH４
０ １００１
－０ ２１３７
SMSS１ Ｇ pH１０
０ ２２０８
－０ ４４１８
SMSS２ Ｇ pH４
SMSS２ Ｇ pH１０
０ ０８９５
０ ２０３１
－０ ４５６９
The pa s s i va t i onr eg i on wi d t h and pa s s i va t i on cu r r en t( Ip)a r eve r r t an tma t e r i a l sc o r r o s i on yimpo cha r a c t e r i z a t i on pa r ame t e r s．Thepa s s i va t i onr eg i on wi d t hi swi de r( Tab l e２)． I tshowst ha tt hes t ab i l i t y o ft he me t a lpa s s i va t i oni sg r e a t e r．The s er e su l t si n Tab l e２sugge s tt ha tSMSSs amp l e shaveabe t t e r s s i va t i ngab i l i t na l ka l i nec ond i t i ont hani na c i d i c pa yi c ond i t i on． I nt hes amepHc ond i t i on,t hes t ab i l i t f yo SMSS１s amp l e ′ spa s s i vef i lmi ss t r onge rt hant ha to f SMSS２ s amp l e by c ompa r i ng pa s s i va t i on r eg i on wi d t handIp．Thede c r e a s eo fIpi nSMSS１s amp l e wa sexp l a i nedbyt ha tt hepa s s i vef i lmi sd i f f i cu l ti n d i s s o l v i ngands t r onge rox i de sp r even t i ngf r a c t u r eo f
０ ３１３８
０ ６６２５ ０ ６５９９
６ ３×１０－３ ２ ５×１０－３ ５ ３×１０－３
s s i vel aye r．Sot he pa s s i va t i onab i l i t fs amp l e pa yo SMSS１i ss l i t l t r onge rt han t ha to fs amp l e gh ys SMSS２． I tr eve a l st ha tt he pa s s i vef i lm o fSMSS１ ha sabe t t e r pr o t e c t i vec apa c i t n pH １０ y．TheIp i cond i t i oni sl e s st hant ha ti npH４cond i t i on,depen Ｇ － d i ngont he g r adua l l nc r e a s i ng OH i ons．When yi t hepHi sh i r,i ti s mo r ed i f f i cu l tf o rt he me t a l ghe sur f a c et oa c t i va t e．Thec a t hod i cpo l a r i z a t i oni ssup Ｇ r e s s ed,f ur t he rp r e v e n t i ngt hed i s s o l u t i on so fme t a l． p Whenc a t i on i c s ga t he ri n ac e r t a i n conc en t r a t i on, ma i nox i d i z ed p r oduc t so fa l l oye l emen t s wi l lf o rm t he rmodynami cs t ab l epha s e．Cur r en tg r adua l l Ｇ y de c r e a s edwi t ht hei nc r e a s eo fpo t en t i a l,a ch i ev i ngt he
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
１１５９
s s i va t i on．The r e wi l lbeas t ab l ep r ope r t he pa y ont s s i va t i onr eg i ono fpo l a r i z a t i oncu r ve． pa
s t ab i l i t fpa s s i vef i lm havebe enenhanc edi na l ka Ｇ yo l i necond i t i on．Andi nt hes amepH cond i t i on,t he who l eimpedanc eo fSMSS１ s amp l ei sl a r rt han ge ha to fSMSS２s amp l e,wh i chi sa l socons i s t en twi t h ２ ２ EI Sana l s i so fSMSSs amp l e si nd i f f e r e n tpH t y i t s po l a r i z a t i on cur vecha r a c t e r i s t i c．I ta l so p r ove s c ond i t i on s ha tt he pa s s i va t i on ab i l i t fs amp l e SMSS１ i s Twok i ndso fs amp l e sshowobv i ouss t ab l epa s Ｇ t yo t r onge rt hant ha to fs amp l eSMSS２． s i va t i onr eg i on by ana l i ng po l a r i z a t i on cu r ve si n s yz n add i t i on,t he pha s eang l ei nF i ２( b)i s d i f f e r en tpH c ond i t i ons．Soapa s s i va t i onr eg i onpo Ｇ I g [ ２１] ( ) ( , ) l os e rt o９０ °t hant ha ti nF i ２ a ． I tr eve a l s t en t i a l －０ １ V po l a r i z a t i ont imeo f１h wa s muchc g he pa s s i vef i lm f o rmedi na l ka l i necond i t i on wa s cho s en t of u r t he rs t udy pa s s i va t i on behav i o ro f t r esmoo t handun i f o rm．Al lpha s eang l e si nF i ２ SMSSand me a su r e EI S．The EI S andf i t t i ng ＧEI S mo g r opt owa rd０ °a tt heh i r equenc i e s,i nd i c a t i ng l o t so fSMSSa t－０ １Vi n３ ５ ma s s％ NaCls o l u Ｇ d ghf p ha tt heimpedanc ei sdomi na t edbyt heso l u t i onr e Ｇ t i ons wi t h va r i ous pH va l ue sa r eshowni nF i ２ t g ( i s t anc ei nt h i sf r equenc ange． I ti sno t i ngt ha tt he Bodepha s eang l ep l o t si nwh i chpo i n ti st heexpe r i Ｇ s yr s eang l ede c r e a s e ss i i f i c an t l owa rdl owe rva l Ｇ men t a lda t aandt hel i nei sf i t t i ngda t a)． pha gn yt si nt hel owf r equenc eg i on,demons t r a t i ngt ha t Thef o rma t i ono fpa s s i vef i lmsc r e a t e sd r ama t i c ue yr heimpedanc ea c t sa spur er e s i s t anc eo fpa s s i vef i lm． i nc r e a s ei nimpedanc eandshowsc apa c i t i veimped Ｇ t r,t hepha s er ema i nsc l os et o９０ °ove rawi de anc e( t he Nyqu i s tp l o t so fF i ２)．Mo r eove r,i t Howeve g angeo ff r equenc i e s,i nd i c a t i ngt ha tt hepa s s i va t i on me anst ha tSMSSa tt h i spo t en t i a lf o rmsar e l a t i ve l y r i def i lm p r e s en t sont hesur f a c ei na l lso l u t i ons． s t ab l epa s s i vel aye ri n bo t hs o l u t i ons．I ti sshown ox i r equenc ime cons t an to f W s t em t ha tt heimpedanc eo fs amp l e si nc r e a s e s wi t hi n Ｇ The h gh f yt ys SMSS１)i sa s s o c i a t e dwi t ht hec ha r et r ans f e rp r oc e s s c r e a s i ngpH,f u r t he ri nd i c a t i ngt ha tp r o t e c t i onand ( g
( a),( b)pH４; ( c),( d)pH１０．
F i ２ Nyqu i s tandBod ep l o to fSMSS １andSMSS ２a t－０ １Vi n３ ５ma s s％ NaC ls o l u t i onwi t hd i f f e r en tpHv a l u e s g
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
１１６０
(W ox i da t i on)wh i l et hes e c ondl owf r equenc ime yt c ons t an ti sa s s o c i a t ed wi t hanads o r t i onps eudo c a Ｇ p [ ２２] c i t anc e ． pa Theexp l ana t i ono fEI S( abou tpa s s i va t edme t a l su r f a c e)ha sr a i s edal o to fd i f f e r en t mode l s．Ba s ed ont her e s e a r cho f３１６Ls t e e lpa s s i vef i lm byBo i s s y [ ] and No rmand２３ a s we l la so t he rr e s e a r che r s ′ [ ] wo rks２４Ｇ２８ ,t he mo s tapp r op r i a t eequ i va l en tc i r cu i t d i ag r am f o r SMSS s amp l e s wa s cho s en．El e c t r o Ｇ chemi c a limpedanc espe c t r o s c opyus et heequ i va l en t c i r cu i to fF i ３． I nt h es i m u l a t i o no fe u i v a l e n tc i r Ｇ g q cu i t,cons t an tpha s ee l emen t( CPE)i ns t e ado fpu r e c apa c i t anc ee l emen twa sus ed．TheCPEimpedanc e [ ２９] ( ) ( ) : ZCPE c anbeexpr e s s edbyEq １ ( ZCPE ＝ ( ω)－n/Q １) j whe r e,Q andn a r eCPEc ons t an t s．
F i ３ Equ i v a l en tc i r c u i tf o rt h eSMSSi n３ ５ma s s％ g NaC ls o l u t i onwi t hv a r i ou spH
sr e cogn i z eda st hecha r a c t e r i z a Ｇ Thef a c t o rn i [ ] t i on o fun i f o rmi t f pa r ame t e r s３０ wh i ch a lways yo l i e sbe twe en０ ５and１ ０． I ta l soshowst hed i spe r Ｇ s i one f f e c tont hesur f a c er oughne s s．Whenn ＝１,
t heCPEde s c r i be sani de a lc apa c i t o r．Fo r０ ５＜n＜ , １ ０ t he CPE de s c r i be sad i s t r i bu t i ono fd i e l e c t r i c r e l axa t i ont ime si nf r equenc c e．Whenn ＝０ ５, yspa
t heCPEr ep r e s en t sa Wa rbur ewi t hd i f Ｇ gimpedanc f us i ona lcha r a c t e r．Thef i t t ed pa r ame t e r sa r el i s t ed i nTab l e３．RSi st heso l u t i onr e s i s t anc e,R１ i st he r r e spondst ot he r e s i s t anc eo ft hepa s s i vef i lm,Q１co , eudoc apa c i t anc eo ft hef i lm expr e s s edus i ngt he ps CPE１． R２i sacha r r ans f e rr e s i s t anc eo ft hep i t Ｇ get , ( ) t i ngho l e andQ２ CPE２ co r r e spondst oacha r ge t r ans f e rc apa c i t anc eo ft hep i t t i ng ho l e．F i t t i ngex Ｇ r imen t a lda t af r om F i ２a r es imu l a t edbyequ i va Ｇ pe g ２ , fva r i anc ei nTab l e３ l en tc i r cu i ta swe l la st heX o wh i cha r er e l a t i ve l l li n magn i t ude．The s er e Ｇ ysma su l t sc ande t e rmi net heequ i va l en tc i r cu i td i ag r ams mo r esu i t ab l ef o rt heexpe r imen t．Equ i va l en tc i r cu i t mode lshowst ha tpa s s i vef i lm doe sno tcomp l e t e l y cove rt heme t a lsur f a c e,wh i chduet osur f a c er oughＧ ne s sando t he rr e a sonst ha tc anc aus et hed i spe r s i on e f f e c t．Thepa s s i vef i lmi sno taun i f o rml aye r,bu ta
Tab l e３ Equ i v a l en tc i r c u i tpa r ame t e r si n３ ５ma s s％ NaC ls o l u t i onwi t hv a r i ou spHa t－０ １V S t e e lt ype andpH
RS/ ( Ωcm２)
SMSS２ Ｇ pH４
２ ０８７
SMSS１ Ｇ pH４ SMSS１ Ｇ pH１０ SMSS２ Ｇ pH１０
R１/ ( Ωcm２)
Q１/ ( F cm－２)
n１
Q２/( Fcm－２)
n２
R２/ ( Ωcm２)
X２/
１０－３
５ １３６
１ ６２５×１０
６ ４９５×１０
０ ９０６
６ ７１３×１０
０ ７２２
１ ０７３×１０
１ ９０９６
５ ３２２
３ １８２×１０５
１ ４７７×１０－５
０ ９３４
４ ０９１×１０－５
０ ８２１
１ ８３２×１０６
２ ３５５５
４ ２１１
５
１ ０３２×１０５
２ ３７７×１０５
－５
６ ８０２×１０－５
１ ９２９×１０－５
r ousf i lmo fs emi c onduc t o rcha r a c t e r i s t i c３１Ｇ３３ ． po Whens imu l a t i ngequ i va l en tc i r cu i t,t hepo l a r i Ｇ z a t i onr e s i s t anc e Rp i sde c i ded byt he R１ and R２ , name l anbes e enf r om Tab l e３, yRp＝R１ ＋R２ ．Asc , i na l ka l i necond i t i on bo t hR１ andR２i nc r e a s e swi t h
０ ９２２ ０ ９４６
－５
６ ９３４×１０－５ ２ ２１８×１０－５
０ ７７８ ０ ８１９
５
３ ０３７×１０４ ８ ８４６×１０５
２ ３１９１ ２ ８５４６
f i lm de c r e a s e s．Th i si scons i s t en twi t ht hepa s s i va Ｇ t i oncur r en tdens i t v a l u e so b t a i n e di nT a b l e２． T h e y r o t e c t i onab i l i t fpa s s i vef i lmo fs amp l eSMSS１i s p yo h i rt hant ha to fs amp l eSMSS２,a sshownbyt he ghe h i rf i lm r e s i s t anc e．Att hes amet ime,CPE１o f ghe amp l ei sl owe r． R２ o fs amp l eSMSS１i ss i Ｇ t hei nc r e a s eo fpHva l ue． Sot heRpva l uei nt hea l ka Ｇ SMSS１s g i f i c an t l i r．TheRp o fs amp l eSMSS１i smuch l i necond i t i oni sh i rt hant ha ti nt hea c i d i cc ond i Ｇ n yh ghe ghe i rt hanRp o fs amp l eSMSS２．Thepa s s i vef i lm t i on． I tshowst ha t,duet oi nc r e a s edpH,ma t e r i a l s h ghe t ruc t ur eo fs amp l eSMSS１i s mo r es t ab l e,andc a Ｇ o t e c t i onc apa c i t l lenhanc e．Thef i lm wi l lhave s pr y wi a c i t o f a s s i v e f i l mi s e n h a n c i n ． I na c i d i cN a C l s o Ｇ h i h e rs t a b i l i t a n dc o m a c t n e s sa f t e r o l a r i z a t i o n． p y p g g y p p , , u t i on whe t he rs amp l eSMSS１o rs amp l eSMSS２, I na dd i t i on n１ a ndn２ v a l u e sa r eh i na l k a l i n ec ond i Ｇ l ghi heR２ wa ssma l l e rt han R１ ．Th i sc anbeexp l a i ned t i on,wh i c hi l l us t r a t e st ha tt hepa s s i vef i lm o fs t a i n Ｇ t l e s ss t e e lf o rmedi na l ka l i nec ond i t i oni s mo r eun i Ｇ byt hef a c tt ha tt hee l e c t r o l t eso l u t i on wa spa r t l y y [ ] f o rmandcompa c t．Andt hepa s s i vef i lmi smo r es t a Ｇ sho r t Ｇ c i r cu i t edi nt hemi c r opo r e so ri n t e r s t i t i a l s３４ ． b l e,t her e Ｇ s s i va t i onab i l i t l lbeimp r oved．I n pa y wi , t hes amepHc ond i t i ons i ti sobs e r vedt ha tt heR１o f ２ ３ XPSde t hpr o f i l i ngo fSMSSs amp l e sa td i f f e r Ｇ p s amp l eSMSS２i sl e s st hant ha to fs amp l eSMSS１, en tpHc ond i t i on s i nd i c a t i ng t ha tt he c o r r o s i on r e s i s t anc eo f pa s s i ve Thr ought heana l i so fpo l a r i z a t i oncur ve sand ys [
]
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
EI S,i tp r ove st ha tt he pa s s i ve f i lm o fs amp l e SMSS１i smo r es t ab l et hant ha to fs amp l eSMSS２i n t hes ame pH c ond i t i on．Att hes amet ime,i ta l s o r ove st ha tt hepa s s i va t i onab i l i t fSMSSs amp l ei n p yo a l ka l i necond i t i oni ss t r onge rt hant ha ti na c i d i cc on Ｇ d i t i on．I no r de rt of u r t he rexp l a i nt he p r ope r t f yo s s i vef i lm, XPS dep t hp r o f i l i ng da t ao f SMSS pa s amp l e swi l lbedonei nbo t hc ond i t i ons: ( ) １ I n３ ５ ma s s％ NaClso l u t i onso fpH ４, －０ １Vv s． SCE ( l a r i z a t i ont imei s１h)． po ( ２)I n３ ５ ma s s％ NaCls o l u t i onso fpH １０, ( ) －０ １Vv s． SCE po l a r i z a t i ont imei s１h ． I nana l i so fXPSs t anda r dspe c t r a,Fee l emen t ys c o r r e spondst ot hepe akb i nd i ngene r f７０７eV, gyo ( , , , andt heFe Ｇ ox i de s FeO Fe２O３ Fe３O４ e t c )a r ei n t hev i c i n i t f７１０eV;Cre l eme n tc o r r e s st ot h e yo pond
１１６１
e akb i nd i nge n e r f５７４ ４eV,andt heCr Ｇ ox i de s p gyo (ma ) i n l OH) a n dC r O a r e i nt h ev i c Ｇ yCrO３ ,Cr( ３ ２ ３ i n i t f５７７eV． I no rde rt oge tbe s tr e su l t s,a l lt he yo dep t hp r o f i l i ng spe c t rums we r ep r oc e s s ed i nt he s ameway． Fo rexamp l e,as amp l esur f a c ei nF i ４ s g i ( ) ana l z edbyl aye rbyl aye r １nm pe rl aye rt oob t a i n y Fe ２p３/２andCr ２p３/２o r i i na lb i nd i ngene r c t rum g gyspe o fSMSS１ ( i npH４)． Fr omou t s i det oi ns i de,Feand Cra r el oc a t edi nt heh i rb i nd i ngene r akt han ghe gype t heb i nd i ngene r fe l emen t a ls t a t e,wh i chshows gyo t ha tt heox i de sf o rmi nt hepa s s i vef i lm．Wi t ht hei n Ｇ , , c r e a s eo fdep t h f r om ou t s i det oi ns i de FeandCr a r ef oundbyt he i re l emen t a ls t a t e,i nd i c a t i ngt ha ti t , ha sbe enobs e r vedwi t h i nt he i rma t r i x．The r e f o r ei t c anbeconc l udedt ha tt heox i da t i ons t a t e so fFeand Cra r ep r e s en ti nt hepa s s i vef i lm．
( a)Fe ２p３/２; ( b)Cr ２p３/２．
F i ４ En e r e c t r umo fSMSS １( i npH４)s amp l ewi t hd ep t hchang e g g ys p
Theo r i i na lXPSspe c t r aa r ef u r t h e ra n a l z e dby g y LLS ( L i ne a rLe a s tSqua r e s)way．Asa r onspu t Ｇ goni , t e r i ngdep t hchange s chemi c a ls t a t ed i s t r i bu t i onso f FeandCri nt hepa s s i vef i lm we r eob t a i nedi ntwo i t i onsf r om F i ５．Wi t ht hei nc r e a s eo f pH cond g , spu t t e r i ngdep t hc on t en t st endt obes t ab l e． Crno r Ｇ ma l l i b i t st hr e echemi c a ls t a t e si nt he pa s s i ve yexh f i lm．Whent hespu t t e r i ngdep t hi ssma l l e r,Cri sde Ｇ ( ) r i vedf r omt heCr OH ３ ．Wi t hi nc r e a s i ngt hespu t Ｇ t e r i ngdep t h,Cri sde r i vedf r om t heCr２O３ ．When t hespu t t e r i ngdep t hi sc l o s et ot hema t r i x,Cri se l e Ｇ [ ４, ３５] men t a ls t a t e ．Ac c o r d i ng t ot he me t hod men Ｇ t i onedby Gebe r t,t het h i ckne s so ft hepa s s i vef i lm c anbee s t ima t eda st hedep t h whe r et heox i dec on Ｇ t en td r opst ot he mi dva l uebe twe ent hei n i t i a land [ , ] r e s i dua loxygenc on t en t３６ ３７ ．Ac c o r d i ngt oF i ４ gs , and５ i tc anbej udgedt ha tt hesput t e r i ng dept h
( ５nmi ndep t h)c anbecons i de r eda st het h i ckne s s o fpa s s i vef i lm． Ther e a sonwhyt hepa s s i vef i lm o fFe ＧCra l l oy /Fer ha sap r o t e c t i onc apa c i t st ha tt heCr a t i oi s yi r e a t l r oved,andt he Cr Ｇ ox i dei sa p r o t e c t i ve g yimp e f f e c t i vecomponen tf o rt hepa s s i vef i lm．Theh i r ghe r a t i or e su l t si n mo r ee f f e c t i vec apa c i t f pa s s i ve yo f i lm p r even t i ng me t a lco r r os i on．TheFe Ｇ ox i deand Cr Ｇ ox i deo fa t omi cc on c e n t r a t i onr a t i oi n s i d et hed e t h p o f６nma r el i s t edi nTab l e４． Bo t hi na c i d i canda l ka Ｇ l i necond i t i ons,Cr Ｇ ox i decon t en to fs amp l eSMSS１ i sh i rt hant ha to fs amp l eSMSS２i nt hepa s s i va Ｇ ghe t i onl aye r． I nt h i st e s t,t hepa s s i vef i lmi scompos ed o fCr Ｇ ox i deand Fe Ｇ ox i del aye r s．MoOn－ i onsf r om t hepa s s i vef i lm changet heo r i i na lan i on un i t i ng g wi t hc a t i ons,p r omo t i ng O２－ i onsmi r a t i on,r e su l Ｇ g － , t i ngi nt hef o rma t i ono fCr Ｇ ox i de h i nd e r i ngC li on s
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
１１６２
( a)SMSS１i npH４; ( b)SMSS２i npH４; ( c)SMSS１i npH１０; ( d)SMSS２i npH１０．
F i ５ XPSd ep t hp r o f i l e so fpa s s i v a t e dSMSS g
Tab l e４ Fe Ｇ ox i d eandCr Ｇ ox i d ea t omi cc onc en t r a t i on si nt h er ang eo f１－６nm ma s s％ At omi cc onc en t r a t i onsi nd i f f e r en tdep t hs
Samp l e
Ox i de
SMSS１ Ｇ pH４
Fe Ｇ ox i de Cr Ｇ ox i de
７０ ７３３９ ２９ ２６６１
７６ ０２５３ ２３ ９７４７
６２ １７４７ ２４ ２４１６
３６ ０９３５ １６ ２４７０
１３ ３２７８ ７ ８８８２
５ ９２８５ ３ ２０５５
Fe Ｇ ox i de Cr Ｇ ox i de
７６ １１６１ ２３ ８８３９
７９ ９０３４ ２０ ０９６６
６４ ３５８１ ２２ ３７０４
３３ ０１７０ １４ ７８６１
１７ ５６９１ ７ ４４１０
５ ７１２１ ３ ２５５７
SMSS２ Ｇ pH４ SMSS１ Ｇ pH１０ SMSS２ Ｇ pH１０
Fe Ｇ ox i de Cr Ｇ ox i de
Fe Ｇ ox i de Cr Ｇ ox i de
１nm
６４ ７４７１ ３５ ２５２９
８２ ５３４３ １７ ４６５７
２nm
７７ １０９６ ２２ ８９０４
８５ ５２０５ １４ ４７９５
t oen t e rt hepa s s i vef i lmand mak i ngf i lm mo r es t a Ｇ [ ] b l e３８ ．Duet oCr Ｇ ox i deads o rbedont hesu r f a c e,t he o r i i na lan i on Ｇ s e l e c t i ve pa s s i vef i lm wou l d be c ome g c a t i on Ｇ s e l e c t i ve．Thus,i tc anbeexc l udedbye r o s i on － andde s t ruc t i ono fCl i onsont hepa s s i vef i lm．The s s i vef i lmc ang r e a t l r ovet hec o r r o s i onr e s i s t Ｇ pa yimp [ ] anc e３９ ．Add i ng W no ton l r ove st he pa s s i ve yimp [ ] f i lm p r ope r t fSMSS４０ bu ta l s op r omo t e s Mot o yo
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２４ １３１４ １４ ６２６８
４５ １２２６ １３ ２３６０
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１４ ０９０２ ６ ６８２９
１８ ７９６１ ６ ６７５７
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４ ５３２７ ３ ００９６
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４１ ４２ t r ans f o rmi n t o MoO２－ ．MoO２－ ndFe２＋ f o rm ４ ４ a FeMoO４ ,andFeMoO４ wi l lmakemo r eCr Ｇ ox i deand [, ] Fe Ｇ ox i def o rmedont hepa s s i vef i lm ４ ４３ ．Asshown /Fer i n Tab l e４,t he Cr a t i oo fs amp l e SMSS１i s , s l i t l i rt hant ha to fs amp l eSMSS２ wh i ch gh yh ghe wi l limp r ovet heb l ock i ngc apab i l i t ha tpa s s i vef i lm yt ha sbe en damaged by Cl－ i ons．I ti l l us t r a t e st ha t ( ) r o t e c t i o no f s a m l eS M S S １ W c o n t a i n i n i sb e t Ｇ p p g [ , ]
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
t e rt hant ha to fs amp l eSMSS２ (Wf r e e),wh i cha r e c ons i s t en twi t he l e c t r o chemi c a lt e s tr e su l t s．
３ Conc l u s i on s
( １)I nt hes amepH c ond i t i ons,t hes t ab i l i t y and un i f o rmi t f pa s s i vef i lm o fs amp l e SMSS１ yo ( c on t a i n i ng W)a r ebe t t e rt hant ho s eo fSMSS２s amＧ , l e i n d i c a t i n t h a t t h e a s s i v a t i o na b i l i t o fs a m l e p g p y p SMSS１i ss t r onge rt hant ha to fs amp l eSMSS２．The SMSSha sas t r onge rpa s s i va t i onab i l i t na l ka l i ne yi c ond i t i ont hani na c i d i cc ond i t i on,andt he pa s s i ve f i lma l soha sabe t t e rpr o t e c t i vec apa c i t y． ( ２)Thr oughana l z i ngt heEI Sexpe r imen t a l y r e su l t sand s imu l a t i ng equ i va l en tc i r cu i td i ag r am, t hepa s s i vef i lm c an bec ons i de r edt o bea po r ous s t ruc t ur ewi t hs emi c onduc t o rcha r a c t e r i s t i c s．TheRp va l uei sh i ri na l ka l i nec ond i t i ont hani na c i d i c ghe c ond i t i on,wh i chshowst ha tSMSSp r o t e c t i onc apa c Ｇ i t senhanc ed,andt hepa s s i vef i lm ha sh i rs t a Ｇ yi ghe b i l i t ompa c t ne s sa f t e r po l a r i z a t i on．I nt he y and c s amepH cond i t i ons,t he pa s s i vef i lm s t ruc t u r eo f SMSS１i s mo r es t ab l eanddens e r．The pa s s i va t i on c apa c i t fSMSSha sbe eni nc r e a s eda c c o r d i ng l yo y． ( ３)XPSdep t hpr o f i l i ngr e su l t sno ton l on Ｇ yc f i rm t heabovec onc l us i ons,bu ta l s osugge s tt ha t add i ng W c anpr omo t e mo r eCr Ｇ ox i deandFe Ｇ ox i de f o rmedont hepa s s i vef i lm．Moand W s rg i e sc an yne r educ et hedeva s t a t i on o f Cl－ i onsont he pa s s i ve , f i lm andpr o t e c t i vec apa c i t fpa s s i vef i lmha sbe en yo imp r oved． ( ４)Thepa s s i vef i lmc ompo s i t i onsi na c i d i cand a l ka l i neso l u t i onsa r emo s t l Ｇ ox i deandCr Ｇ ox i de． yFe Thes t ruc t ur eo fpa s s i vef i lmi sa mi x t u r eo fCr Ｇ ox Ｇ i de sandFe Ｇ ox i de s． Re f e r enc e s:
[ １] A．Ko c i an,C．Don i k,M． J enko,Co r r o s． Sc i． ４９ ( ２００７)２０８３ Ｇ j ２０９８． [ ２] MF．Mon t emo r,MGS． Fe r r e i r a,NE．Hak i k i,Co r r o s． Sc i． ４２ ( ２０００)１６３５ Ｇ １６５０． [ ３] S．Mi s ch l e r,A．Voge l,HJ．Ma t h i eu,D． Lando l t,Co r r o s． Sc i． ３２ ( １９９１)９２５ Ｇ ９４４． [ ４] M． Sán c h e z,H．Mahmoud,J． So l i dS t a t eE l e c t r． １６ ( ２０１２)１１９３ Ｇ １２０２． [ ５] D N． Zou,R． L i u,J． L i,W． Zhang,D．Wang,Y．Han,J． I r on S t e e lRe s． I n t． ２１ ( ２０１４)No ６,６３０ Ｇ ６３６． [ ６] X C．Han,J．L i,KY．Zhao,W．Zhang,J．Su,J． I r onS t e e l Re s． I n t． ２０ ( ２０１３)No ５,７４ Ｇ ７９． [ ７] C O A．Ol s s on,D．La ndo l t,E l e c t r o c h im．Ac t a４８ ( ２００３)１０９３ Ｇ １１０４． [ ８] S Y．Kim,H．Kim,HS．Kwan,Ma t e r．Co r r o s．５７ ( ２００６) ８３５ Ｇ ８４２．
１１６３
[ ９] S．Haup t,HH． S t r ehb l ow,Co r r o s． Sc i． ３７ ( １９９５)４３ Ｇ ５４． [ １０] HW．Hoppe,S．Haup t,HH．S t r ehb l ow,Sur f． I n t e r f a c e Ana l． ２１ ( １９９４)５１４ Ｇ ５２５． [ １１] Ž．Pe t r ov i c,N． La ç i,M．Me t i ko š ＧHukov i c,R．Bab i c,J． So l Ｇ j i dS t a t eEl e c t r． １５ ( ２０１０)１２０１ Ｇ １２０７． [ １２] J．Di ng,L． Zhang,M． Lu,J．Wang,Z．Wen,W．Hao,App l． Sur f． Sc i． ２８９ ( ２０１４)３３ Ｇ ４１． [ １３] A．Da v o o d i,M．Pak s h i r,M．Ba b a i e e,G R．Eb r ah imi,Co r r o s． S c i． ５３ ( ２０１１)３９９ Ｇ ４０８． [ １４] E． J ame s,Conc r e t eEng． I n t． ６( ２００２)６４ Ｇ ６７． [ １５] D V．Va l,MG． S t ewa r t,S t r uc t． Sa f． ２５ ( ２００３)３４３ Ｇ ３６２． [ １６] K M．Kim,K Y．Kim,J． Powe rSou r c e s１７３ ( ２００７)９１７ Ｇ ９２４． [ １７] W． J i ang,KY．Zhao,D．Ye,J．L i,Z D．L i,J．Su,J． I r on S t e e lRe s． I n t． ２０ ( ２０１３)No ５,６１ Ｇ ６５． [ １８] D．Ye,J．L i,W． J i a ng,J．Su,K．Zh a o,Ma t e r．De s． ４１ ( ２０１２) １６ Ｇ ２２． [ Su,KY．Zhao,W． J i ang, １９] YR．L i u,D．Ye,QL．Yong,J． J． I r onS t e e lRe s． I n t． １８ ( ２０１１)No １１,６０ Ｇ ６６． [ ２０] Y F．Ch e n,J L．Luo,E l e c t r o c h im．Ac t a４４ ( １９９９)２９４７ Ｇ ２９５７． [ ２１] A． Sa a t ch i,MA．Go l o z a r,K．Ra e i s s i,J．App l．El e c t r o chem． ４０ ( ２０１０)４５７ Ｇ ４６１． [ ２２] R S．L i l l a r d,GS．Kanne r,L L．Da emen,El e c t r o ch im．Ac t a ４７ ( ２００２)２４７３ Ｇ ２４８２． [ ２３] C．Bo i s s A．Dumon t,B．No rmand,El e c t r o chem．ComＧ y,C mun． ２６ ( ２０１３)１０ Ｇ １２． [ ２４] A A．He rma s,MS．Mo r a d,Co r r o s． S c i． ５０ ( ２００８)２７１０ Ｇ ２７１７． [ ２５] B．Gu i t i án,X R．Nó v o a,B． Pug a,E l e c t r o c h im．Ac t a． ５６ ( ２０１１)
７７７２ Ｇ ７７７９． [ ao,X G．L i,App l．Sur f．Sc i． ２５８ ２６] H．Luo,C F．Dong,K．Xi ( ２０１１)６３１ Ｇ ６３９． [ ２７] V．Gu i ñón ＧP i n a,A． I a l ＧMuño z,J．Ga r c í a ＧAn t ón,Co r r o s．S c i． gu ５３ ( ２０１１)５７５ Ｇ ５８１． [ ２８] A．Ko c i an,D K．Me r l,M．J enko,Co r r o s．Sc i．５３ ( ２０１１) j ７７６ Ｇ ７８３． [ ２９] R A．An t une s,MC L．Ol i ve i r a,G．Et t,V．Et t,I n t． J．En Ｇ ( ) e r s． ３６ ２０１１ １２４７４ Ｇ １２４８５． g．Re [ ３０] A．Popova,E．Soko l ova,S．Ra i cheva,M．Chr i s t ov,Co r r o s． Sc i． ４５ ( ２００３)３３ Ｇ ５８． [ ３１] AK． I ve r s en,Co r r o s． Sc i． ４８ ( ２００６)１０３６ Ｇ １０５８． [ i,M． Zhu,J． So l i dS t a t eEl e c t r． １８ ３２] Z J． Zheng,Y．Gao,Y．Gu ( ２０１４)２２０１ Ｇ ２２１０． [ ３３] L A S．R i e s,M．DaCunh aBe l o,MG S． Fe r r e i r a,I L．Mu l l e r, Co r r o s． Sc i． ５０ ( ２００８)６７６ Ｇ ６８６． [ ３４] C．Hi t z,A．La s i a,J．El e c t r oana l．Chem． ５００ ( ２００１)２１３ Ｇ ２２２． [ ３５] C F．Chen,R J． J i ang,J S．Qi an,S Q．Zheng,Ac t aPhys． Ch im． S i n． ２５ ( ２００９)１２１３ Ｇ １２１８． [ ３６] A．Gebe r t,K． Buchho l z,A． Leonha r d,K．Mumme r t,J． Eck Ｇ e r t,L． Schu l t z,Ma t e r． Sc i．Eng．A２６７ ( １９９９)２９４ Ｇ ３００． [ ３７] MJ．Ca rme z im,A M．S imõ e s,MF．Mon t emo r,M．DaCunh a Be l o,Co r r o s． Sc i． ４７ ( ２００５)５８１ Ｇ ５９１． [ ３８] S．Naga r a an,N．Ra end r an,Co r r o s． Sc i． ５１ ( ２００９)２１７ Ｇ ２２４． j j [ ３９] YH．L i n,R G．Du,R G．Hu,C J．L i n,Ac t aPhys．Ch im． S i n． ２１ ( ２００５)７４０ Ｇ ７４５． [ ４０] A． I rhz o,Y． Segu i,N． Bu i,F．Dabo s i,Co r r o s． Sc i． ２６ ( １９８６)
７６９ Ｇ ７８０． [ ４１] J S．Kim,P J．X i a ng,K Y．Kim,Co r r o s i on６１ ( ２００５)１７４ Ｇ １８３． [ ４２] K M．Kim,J H．Kim,K Y．Kim,ECST r a n s． ２５ ( ２００９)１８２３ Ｇ １８３２． [ ４３] KH．Lo,C H．Shek,J K．L．La i,Ma t e r．Sc i．Eng．R ６５ ( ２００９)３９ Ｇ １０４．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( １ ２):１ １ ５ ６ Ｇ １ １ ６ ３
Pa s s i v a t i onBe ha v i o r so fSupe rMa r t e n s i t i cS t a i n l e s sS t e e li n We akAc i d i cand We akAl ka l i neNaC lSo l u t i on s １ １ J i anKANG１ , JunLI１ , Kun Ｇ Ｇ l ong YONG２ , J i eSU２ yuZHAO , XuanBAI , Qi
( １． I ns t i t u t eo fMa t e r i a l sSc i enc eandEng i ne e r i ng,Kunmi ngUn i ve r s i t fSc i enc eandTe chno l ogy,Kunmi ng６５００９３, yo Yunnan,Ch i na; ２． I ns t i t u t eo fS t r uc t u r a lMa t e r i a l s,Ce n t r a lI r ona ndS t e e lRe s e a r c hI n s t i t u t e,Be i i ng１０００８１,Ch i n a) j Ab s t r a c t:Thepa s s i va t i onbehav i o r so fsupe rma r t ens i t i cs t a i n l e s ss t e e l s( SMSS)we r es t ud i edbypo l a r i z a t i oncu r ve s a tpa s s i vepo t en t i a lo f－０ １Vandi nva r i ousNaCls o l u t i ons,e l e c t r o chemi c a limpedanc espe c t r o s c opy ( EI S)andXＧ r aypho t oe l e c t r onspe c t r o s c opy ( XPS)ana l s i s．El e c t r o chemi c a lt e s tr e su l t sshowedt ha t,i na l ka l i nes o l u t i ons,pa s Ｇ y s i va t i onr eg i onwi d t hwa swi de r,pa s s i va t i oncu r r en twa ssma l l e r,andpo l a r i z a t i onr e s i s t anc ewa sg r e a t e r;t hus,t he s s i vef i lmo fSMSSi na l ka l i nes o l u t i onshadbe t t e rpa s s i va t i onbehav i o r st hant ha ti na c i d i cs o l u t i ons．Thepo l a r i z a Ｇ pa t i oncu r veandEI So fs amp l e sSMSS１andSMSS２ we r ea l s ous edt os t udywh i chs amp l ehadbe t t e rpa s s i va t i onbe Ｇ hav i o r s．Al lr e su l t sdemons t r a t edt ha tpa s s i vef i lms t r uc t u r eo fSMSS１s amp l ewa smo r es t ab l e,andc apa c i t fpa s Ｇ yo s i vef i lm wa senhanc ed．Theimpa c to fa l l oy i nge l emen t sont hepa s s i vef i lm ( SMSS)pa s s i va t i onc apab i l i t sa l s o ywa d i s cus s edbyXPSdep t hp r o f i l i ng,and XPSdep t hp r o f i l i ngshowedt ha tt hec ompo s i t i ono ft hepa s s i vef i lm wa s ma i n l ompo s edo fFe Ｇ ox i deandCr Ｇ ox i de． Sot hepa s s i vef i lms t r uc t u r e swe r emi xedl aye r so fFe Ｇ ox i deandCr Ｇ ox Ｇ yc i de．Feox i da t i onp r oduc tandCrox i da t i onp r oduc twou l dhe l oimp r ovet hep r o t e c t i vep r ope r t fpa s s i vef i lm, pt yo wh i chc ou l dp r omo t et hef o rma t i ono fapa s s i vef i lms t r uc t u r emo r es t ab l e l yanddens y． Ke r d s:supe rma r t ens i t i cs t a i n l e s ss t e e l;pHva l ue;po l a r i z a t i oncu r ve;e l e c t r o chemi c a limpedanc espe c t r o s c opy; ywo XPSdep t hp r o f i l i ng
Supe rma r t ens i t i cs t a i n l e s ss t e e l s( SMSS)wi t h , chan i c a lpr ope r t i e sc o r r o s i onr e s i s t anc eand goodme we l dab i l i t enwi de l l i edi nt hewo r l da s yhavebe yapp a l t e rna t i ve ma t e r i a l st odup l exs t a i n l e s ss t e e l sand c a rbons t e e l,e spe c i a l l no f f sho r ep i l i ne sandt he yi pe o i landga si ndus t r o rc o r r o s i onr e s i s t anc et oCO２ yf and H２S．Co r r o s i onr e s i s t anc eo fs t a i n l e s ss t e e li s c l o s e l e l a t edt ot hec ompo s i t i onandp r ope r t i e so f yr t he pa s s i vef i lm,such a st he s t ab i l i t i t y,dens y, c ompos i t i on and s t ruc t u r e．Gene r a l l he pa s s i ve y,t f i lm o fs t a i n l e s ss t e e lwa sc ompo s edo ftwo pa r t s: t hei nne rl aye rc on t a i n i ngchr omi um ox i de wa st he ; ma i npa r to ft hepa s s i vef i lma saba r r i e rl aye rt he ou t e rl aye rwa s ma i n l ompo s edo fi r onox i deand yc [ ,] hyd r ox i de１ ２ ．Bu tt hepa s s i vef i lm maychangewi t h t hea l l oycompo s i t i on,po t en t i a lo rt hee l e c t r o l t e, y e spe c i a l l o rpHva l ue． yf Theadd i t i ono fmo l r omo t e st heFe Ｇ ybdenum p
ox i deandCr Ｇ ox i def o rmed mo r es t ab l hepa s Ｇ yont s i vef i lm．Add i ng mo l b d e n u m t o s t a i n l e s s s t e e l y [ ３ Ｇ ５] cou l dimp r ovet hep i t t i ngco r r os i onr e s i s t anc e ． I t wasma i n l othef ac ttha tMor educ edCl－ i Ｇ yduet onsga t he r i ngont hepa s s i vef i lm．Thepo l a r i z a t i on cur veshowedt ha t Cl－ i ons t r ong l r ovedt he yimp i t t i n s u s c e t i b i l i t a n dh a d l i t t l ee f f e c to n i r o no x Ｇ p g p y [ ６] i def i lmg r owt hi nt hepa s s i ver eg i ons ．W wa susu Ｇ a l l n t ocomme r c i a ls t a i n l e s ss t e e l,andi t s yaddedi con t r i bu t i ont ot hep r ope r t fp i t t i ngco r r os i onr e Ｇ yo [] s i s t anc ewa ss imi l a rt o Mo．Ol s sonand Lando l t７ s t ud i edt hesur f a c ep r ope r t i e so fa l l oycon t a i n i ng Mo and W．Tungs t a t ewa sf o rmedbyt hei n t e r a c t i ono f WO２－ ndc a t i ons．Thei onshadava r i e t fbehav Ｇ yo ４ a i o r si nt heco r r os i on p r oc e s s:comb i n i ng wi t hc a t Ｇ i ons,r educ i ngt he mob i l i t fi ons,o rsupp r e s s i ng yo [] adso r t i ono fCl－ i ons．Kim e ta l ８ f oundt ha tt he p a c t i va t i ngcur r en tdens i t fdup l exs t e e lcon t a i n i ng yo
Founda t i onI t em: I t em Spons o r edbyEduc a t i onDepa r tmen tSc i en t i f i cRe s e a r chFundPr o e c tf r om YunnanPr ov i nc eo fCh i na ( ２０１２Y５４４) j B i o r aphy: J i anKANG,Ma s t e r; E Ｇma i l: n i_j i an＠１２６ c om; Re c e i v e dDa t e:Oc t obe r２９,２０１４ gemi g Co r r e s i ngAu t ho r:JunLI,Do c t o r,Le c t ur e sh i Ｇma i l:l ９８１＠１２６ c om p; E jwj pond
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
W wa ss l i t l a r rt hant ha to fdup l exs t e e lno t gh yl ge c on t a i n i ng W,bu tt hepa s s i va t i oncu r r en tdens i t f yo dup l exs t e e lc on t a i n i ng Wi sl owe r． I na l ka l i nes o l u t i ons,Fe Ｇ ox i del aye rusua l l s yha , ah i hs t a b i l i t ． H o w e v e r t h eC r Ｇ o x i d el a e rh a sa g y y h i rs t ab i l i t na c i d i cs o l u t i ons．Thee f f e c to fpH ghe yi ont hepa s s i vef i lm o fFe ＧCra l l oysha sbe ens t ud i ed [] [ ] byS t r ehb l ow ９ and Hoppe１０ ．Theyf oundt ha tt he f i lm wa sf o rmed mo r es t ab l na l ka l i nes o l u t i ons, yi andt henumbe ro fFe ( I I I)ox i dei nc r e a s eds i i f i Ｇ gn c an t l ． T h er e s e a r c ho fs t e a d Ｇ s t a t eo x i d ef i l m h a d y y showedt ha tat h i nba r r i e rl aye ro fCr Ｇ ox i dec l o s et o t hef i lme l e c t r o l t ei n t e r f a c ewa sf o rmedont hepa s Ｇ y / s i vef i lm unde rpo t e n t i o s t a t i cc ond i t i on si n０ ５ mo lL [ ] H２SO４ １１ ．An i ons( Cl－ o rS２－ ) i nt hes o l u t i ons,e s Ｇ c i a l l na c i d i cs o l u t i ons,hadh i rc apa c i t r Ｇ pe yi ghe ype [ ] me a t i ngt opa s s i vef i lm o fFe ＧCra l l oys１２ ． I na c i d i c med i a,３０４Land３１６Ls t a i n l e s ss t e e l sc ou l dexh i b i t a c t i ve Ｇ s s i vebehav i o rdu r i nganod i cpo l a r i s a t i oni n pa wh i chH２Ss i i f i c an t l nc r e a s e st hec r i t i c a lcu r r en t gn yi [ ] dens i t t ha l l oys１３ ．S t a i n l e s ss t e e l wa sa l s o yon bo us edi n an a l ka l i neenv i r onmen ta st her e i n f o r c ed c onc r e t e．Thes t a i n l e s ss t e e lc ou l dp r o l ongl i f eand r educ et hedamagec aus edbyt heimpa c to fc o r r o Ｇ [ ] s i on１４ ． I nt he s ea l ka l i nec ond i t i ons,ex t r eme l t h i n y r o t e c t i vef i lm wa ss t r ong l r en tandchemi c a l l p yadhe y s t ab l e． I thadah i l r o t e c t i veox i def i lmt ha tc ov Ｇ gh yp [ ] e r st hes t a i n l e s ss t e e lsu r f a c e１５ ． Ac co rd i ngt ot heex i s t i ngr e s e a r che s,t hec o r r o Ｇ s i onr e s i s t anc eo fs t a i n l e s ss t e e l si sr e l a t edt oi t spa s Ｇ s i vep r ope r t tt hes t udyonSMSSpa s s i vep r op Ｇ y．Bu e r t sr a r e l epo r t ed．The r e f o r e,t he pa s s i va t i on yi yr behav i o ro fSMSSi n we aka c i d i cand we aka l ka l i ne , env i r onmen t swa sr e s e a r ched wh i chi so fg r e a ts i Ｇ g n i f i c anc et of u r t he rexp l a i nt hec o r r o s i onr e s i s t anc e [ ] o fSMSS１６ ． I nt h i spape r,t hepa s s i va t i onbehav i o r o fSMSSbypo t en t i odynami cpo l a r i z a t i onandEI Si n ３ ５ ma s s％ NaCls o l u t i onswi t hpHo f４and１０wa s i nve s t i t ed．Comb i n i ng wi t ht he XPSdep t hp r o f i Ｇ ga l i ng,t hema i ne l emen t se f f e c ti nt hepa s s i vef i lm o f SMSSwa sa l s oexp l o r ed．
１ Exp e r imen t a l
Twok i ndso fsupe rma r t ens i t i cs t a i n l e s ss t e e l s SMSS１andSMSS２we r echo s en,andt her a t i oo fe l Ｇ emen t si ns t a i n l e s ss t e e lwa sba s edonex i s t i ngr e Ｇ [ ] s e a r che s１７Ｇ１９ ．Thes amp l e swe r eme l t edi nt heva cu Ｇ umi nduc t i onme l t i ngf u rna c e,andd i r e c t l c a s t i n t o y i ngo t s．Thea c t ua lc ompo s i t i onso fs t e e ls amp l e sa r e showni nTab l e１．Thes amp l e swe r ep r o c e s s edi n t o ８ mm×８ mm×１５ mmby wi r ecu t t i ng．Al ls amp l e s
１１５７
we r ehe a tt r e a t eda sf o l l ows:ho l d i nga t１０５０ ℃ f o r ３０ mi n,t henquench i ng ( o i lquench i ng),andt emＧ r i nghe a tp r e s e r va t i ona t６５０ ℃f o r２h．Thes amＧ pe l e sa f t e rhe a tt r e a tmen twe r epo l i shedby３６０g r i t, p ８００g r i t,１２００g r i t,and３０００g r i twa t e r r o o fs a n d Ｇ p , , r and we l ded wi t hcoppe r wi r e s wa shed by pape
d i s t i l l ed wa t e ra c e t one and e t hano l．Al ls amp l e s we r es e a l edbyepoxyr e s i nandc u r i nga e n t．Samp l e g s u r f a c ea r e ai sabou t０ ５cm２．Theso l u t i onsf o rt he t e s t sa r ed i f f e r en tpH ( ４,１０)３ ５ ma s s％ NaClso Ｇ ( ) l u t i ons con t a i n i ngoxygen ．Al lexpe r imen t s we r e r f o rmeda t( ２０±１)℃． pe T a b l e１ Ch emi c a lc omp o s i t i o n so fe xp e r ime n t a ls t e e l sma s s％ S t e e l
C
Mn
S i
Cr
Ni
Mo
W
Cu
SMSS２ ０ ０２１ ０ ４０ ０ ２７ １４ ８２ ６ ５ １ ８０
０
１ ４５
SMSS１ ０ ０２１ ０ ４０ ０ ２７ １４ ７８ ６ ５ ２ ０４ ０ ８ １ ４４
The me a sur emen tdev i c eo f po t en t i odynami c l a r i z a t i on cur ve and e l e c t r ochemi c a limpedanc e po spe c t r os copyi sFr anc eB i o ＧLog i c ′ sVSP Ｇ ３００e l e c t r o Ｇ , chemi s t r ns t rumen t andt heso f twa r es t em i s yi ys ECＧLabso f twa r e V１０ １８．Al lexpe r imen t sus et he c l a s s i c a lt hr e e Ｇ e l e c t r odes t em:wo rk i ng e l e c t r ode ys (WE),coun t e re l e c t r ode ( CE)andr e f e r enc ee l e c Ｇ t r ode ( REF)wh i chi sas a t ur a t edc a l ome le l e c t r ode ( SCE)．Thepo t en t i odynami cpo l a r i z a t i oncur vewa s me a sur edwi t has c anr a t eo f１ mV/s．Po t en t i os t a t i c l a r i z a t i onpa r ame t e r sbe f o r e EISt e s ta r ea sf o l Ｇ po : l ows t he me a sur edpo t en t i a lwa s －０ １ Vandt he l a r i z a t i ont imewa s１h．TheEISt e s t swe r econ Ｇ po duc t edbyho l d i ngt hes amp l e sa tas e r i e so fspe c i f i ed t en t i a l si nt hef r equenc ang i ngf r om１００kHzt o po yr １ ０mHz,w i t has i a lamp l i t ud ep e r t u r b a t i ono f１ ０mV． gn TheEISp l o t swe r eana l z edbyZv i ewso f twa r e．Al l y expe r imen t swe r emadet hr e et ime st oensur er ep r o Ｇ duc i b i l i t i r s ts t epi na l lt e s t sa r ep r ep r oc e s s Ｇ y．Thef i ngf o r１０mi ni nt hec a t hod i cpo l a r i z a t i onpo t en t i a l, i no rde rt or emove pa s s i ve f i lm o fa l ls amp l e s f o rmedi nt hea i r． XPSt e s tequ i tus e st hePHI５５００ Ve r s a Ｇ pmen Pr obe XＧ r ay pho t oe l e c t r on spe c t r os cope,and t he t t e rnana l i sso f twa r ei st hePHI ＧMu l t i Pakso f t Ｇ pa ys wa r es t ems．XＧ r ay exc i t a t i on sour c ei s Al Kα ys ( １４８６ ６eV),us edi n２４ ５ W wo rk i ngcond i t i ons． ( ) Tak i ngt heb i nd i ngene r fC１ s ２８４ ８eV a san gyo i n t e rna ls t anda rd,t he pe ako ft he me a sur edspe c Ｇ , t rum ha sbe enco r r e c t ed anda l lt hes amp l e s ′sur Ｇ f a c e sa r es t r i t oe l e c t r onspe c t r ome t e r ppedby a pho a rgoni ongunl aye rbyl aye r．
１１５８
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
WO２－ onp r oduc ed８ ．Thei onsc ansupp r e s st head Ｇ ４ i － nt heco r r os i on,r educ i ngt he so rp t i ono fCl i onsi s i b i l i t fp i t t i ng co r r os i on oc cur r enc e．Ont he pos yo o t he rhand,a c co rd i ngt ot het heo r fpo i n t Ｇ de f e c t s, yo []
２ Re s u l t sandDi s c u s s i on ２ １ Po l a r i z a t i onc u r v e sana l s i so fSMSSs amp l e si n y d i f f e r en tpHc ond i t i on s F i １ showst he po l a r i z a t i on cu r ve so ftwo g ( ) k i ndso fs amp l e si na c i d i c pH ４ anda l ka l i ne ( pH １０)c ond i t i ons．Thee l e c t r o chemi c a lpa r ame t e r sc a l Ｇ cu l a t edf r omt hecu r ve sa r el i s t edi nTab l e２． I nt he ３ ５ ma s s％ NaCls o l u t i ons,Ept and Ecorr o fSMSS s amp l e si npH４ ( F i １( a))a r es l i t l e s st h a nt ho s e g gh yl ( ) ) i npH１０ ( F i １ b ． I tc o u l db ec o n s i d e r e dt h a t t h e g e f f e c to f W wa s mo r eobv i oust oSMSS２s amp l e ′s s s i vef i lm wi t hp i t t i ngc o r r o s i on． I twa sduet ot he pa
t hee l e c t r ondono r sdopeda r ema i n l c an Ｇ yoxygenva c i e si nt hef i lm．Andoxygenva c anc i e sc anr e a c twi t h t heso l u t i ono fOH－ i ons,p r omo t i ngt heg r owt ho f [ ２０] , t hepa s s i vef i lm ．The r e f o r e when pH va l ueo f t heso l u t i oni sh i r,t hes t ab i l i t fpa s s i vef i lm ghe yo [ ] wi l lbes t r onge r２０ ． Sot hep i t t i ngpo t en t i a li sh i r ghe , i na l ka l i necond i t i ont hani na c i d i ccond i t i on wh i ch showst ha tt hepa s s i vef i lmf o rmedha ss t r onge rp i t Ｇ t i ngco r r os i onr e s i s t anc ei na l ka l i necond i t i ons．
F i １ Po l a r i z a t i onc u r v e so fSMSS １andSMSS ２i npH４ ( a)andpH１０ ( b)３ ５ma s s％ NaC ls o l u t i on s g Tab l e２ Ma i ne v a l ua t i onpa r ame t e r so fpo l a r i z a t i onc u r v e s Samp l e
Ept/V
Ecorr/V
( /V Ept－Ecorr)
Ip/(mAcm－２)
－０ ２１７９
０ ３０７４
９ ２×１０－３
SMSS１ Ｇ pH４
０ １００１
－０ ２１３７
SMSS１ Ｇ pH１０
０ ２２０８
－０ ４４１８
SMSS２ Ｇ pH４
SMSS２ Ｇ pH１０
０ ０８９５
０ ２０３１
－０ ４５６９
The pa s s i va t i onr eg i on wi d t h and pa s s i va t i on cu r r en t( Ip)a r eve r r t an tma t e r i a l sc o r r o s i on yimpo cha r a c t e r i z a t i on pa r ame t e r s．Thepa s s i va t i onr eg i on wi d t hi swi de r( Tab l e２)． I tshowst ha tt hes t ab i l i t y o ft he me t a lpa s s i va t i oni sg r e a t e r．The s er e su l t si n Tab l e２sugge s tt ha tSMSSs amp l e shaveabe t t e r s s i va t i ngab i l i t na l ka l i nec ond i t i ont hani na c i d i c pa yi c ond i t i on． I nt hes amepHc ond i t i on,t hes t ab i l i t f yo SMSS１s amp l e ′ spa s s i vef i lmi ss t r onge rt hant ha to f SMSS２ s amp l e by c ompa r i ng pa s s i va t i on r eg i on wi d t handIp．Thede c r e a s eo fIpi nSMSS１s amp l e wa sexp l a i nedbyt ha tt hepa s s i vef i lmi sd i f f i cu l ti n d i s s o l v i ngands t r onge rox i de sp r even t i ngf r a c t u r eo f
０ ３１３８
０ ６６２５ ０ ６５９９
６ ３×１０－３ ２ ５×１０－３ ５ ３×１０－３
s s i vel aye r．Sot he pa s s i va t i onab i l i t fs amp l e pa yo SMSS１i ss l i t l t r onge rt han t ha to fs amp l e gh ys SMSS２． I tr eve a l st ha tt he pa s s i vef i lm o fSMSS１ ha sabe t t e r pr o t e c t i vec apa c i t n pH １０ y．TheIp i cond i t i oni sl e s st hant ha ti npH４cond i t i on,depen Ｇ － d i ngont he g r adua l l nc r e a s i ng OH i ons．When yi t hepHi sh i r,i ti s mo r ed i f f i cu l tf o rt he me t a l ghe sur f a c et oa c t i va t e．Thec a t hod i cpo l a r i z a t i oni ssup Ｇ r e s s ed,f ur t he rp r e v e n t i ngt hed i s s o l u t i on so fme t a l． p Whenc a t i on i c s ga t he ri n ac e r t a i n conc en t r a t i on, ma i nox i d i z ed p r oduc t so fa l l oye l emen t s wi l lf o rm t he rmodynami cs t ab l epha s e．Cur r en tg r adua l l Ｇ y de c r e a s edwi t ht hei nc r e a s eo fpo t en t i a l,a ch i ev i ngt he
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
１１５９
s s i va t i on．The r e wi l lbeas t ab l ep r ope r t he pa y ont s s i va t i onr eg i ono fpo l a r i z a t i oncu r ve． pa
s t ab i l i t fpa s s i vef i lm havebe enenhanc edi na l ka Ｇ yo l i necond i t i on．Andi nt hes amepH cond i t i on,t he who l eimpedanc eo fSMSS１ s amp l ei sl a r rt han ge ha to fSMSS２s amp l e,wh i chi sa l socons i s t en twi t h ２ ２ EI Sana l s i so fSMSSs amp l e si nd i f f e r e n tpH t y i t s po l a r i z a t i on cur vecha r a c t e r i s t i c．I ta l so p r ove s c ond i t i on s ha tt he pa s s i va t i on ab i l i t fs amp l e SMSS１ i s Twok i ndso fs amp l e sshowobv i ouss t ab l epa s Ｇ t yo t r onge rt hant ha to fs amp l eSMSS２． s i va t i onr eg i on by ana l i ng po l a r i z a t i on cu r ve si n s yz n add i t i on,t he pha s eang l ei nF i ２( b)i s d i f f e r en tpH c ond i t i ons．Soapa s s i va t i onr eg i onpo Ｇ I g [ ２１] ( ) ( , ) l os e rt o９０ °t hant ha ti nF i ２ a ． I tr eve a l s t en t i a l －０ １ V po l a r i z a t i ont imeo f１h wa s muchc g he pa s s i vef i lm f o rmedi na l ka l i necond i t i on wa s cho s en t of u r t he rs t udy pa s s i va t i on behav i o ro f t r esmoo t handun i f o rm．Al lpha s eang l e si nF i ２ SMSSand me a su r e EI S．The EI S andf i t t i ng ＧEI S mo g r opt owa rd０ °a tt heh i r equenc i e s,i nd i c a t i ng l o t so fSMSSa t－０ １Vi n３ ５ ma s s％ NaCls o l u Ｇ d ghf p ha tt heimpedanc ei sdomi na t edbyt heso l u t i onr e Ｇ t i ons wi t h va r i ous pH va l ue sa r eshowni nF i ２ t g ( i s t anc ei nt h i sf r equenc ange． I ti sno t i ngt ha tt he Bodepha s eang l ep l o t si nwh i chpo i n ti st heexpe r i Ｇ s yr s eang l ede c r e a s e ss i i f i c an t l owa rdl owe rva l Ｇ men t a lda t aandt hel i nei sf i t t i ngda t a)． pha gn yt si nt hel owf r equenc eg i on,demons t r a t i ngt ha t Thef o rma t i ono fpa s s i vef i lmsc r e a t e sd r ama t i c ue yr heimpedanc ea c t sa spur er e s i s t anc eo fpa s s i vef i lm． i nc r e a s ei nimpedanc eandshowsc apa c i t i veimped Ｇ t r,t hepha s er ema i nsc l os et o９０ °ove rawi de anc e( t he Nyqu i s tp l o t so fF i ２)．Mo r eove r,i t Howeve g angeo ff r equenc i e s,i nd i c a t i ngt ha tt hepa s s i va t i on me anst ha tSMSSa tt h i spo t en t i a lf o rmsar e l a t i ve l y r i def i lm p r e s en t sont hesur f a c ei na l lso l u t i ons． s t ab l epa s s i vel aye ri n bo t hs o l u t i ons．I ti sshown ox i r equenc ime cons t an to f W s t em t ha tt heimpedanc eo fs amp l e si nc r e a s e s wi t hi n Ｇ The h gh f yt ys SMSS１)i sa s s o c i a t e dwi t ht hec ha r et r ans f e rp r oc e s s c r e a s i ngpH,f u r t he ri nd i c a t i ngt ha tp r o t e c t i onand ( g
( a),( b)pH４; ( c),( d)pH１０．
F i ２ Nyqu i s tandBod ep l o to fSMSS １andSMSS ２a t－０ １Vi n３ ５ma s s％ NaC ls o l u t i onwi t hd i f f e r en tpHv a l u e s g
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
１１６０
(W ox i da t i on)wh i l et hes e c ondl owf r equenc ime yt c ons t an ti sa s s o c i a t ed wi t hanads o r t i onps eudo c a Ｇ p [ ２２] c i t anc e ． pa Theexp l ana t i ono fEI S( abou tpa s s i va t edme t a l su r f a c e)ha sr a i s edal o to fd i f f e r en t mode l s．Ba s ed ont her e s e a r cho f３１６Ls t e e lpa s s i vef i lm byBo i s s y [ ] and No rmand２３ a s we l la so t he rr e s e a r che r s ′ [ ] wo rks２４Ｇ２８ ,t he mo s tapp r op r i a t eequ i va l en tc i r cu i t d i ag r am f o r SMSS s amp l e s wa s cho s en．El e c t r o Ｇ chemi c a limpedanc espe c t r o s c opyus et heequ i va l en t c i r cu i to fF i ３． I nt h es i m u l a t i o no fe u i v a l e n tc i r Ｇ g q cu i t,cons t an tpha s ee l emen t( CPE)i ns t e ado fpu r e c apa c i t anc ee l emen twa sus ed．TheCPEimpedanc e [ ２９] ( ) ( ) : ZCPE c anbeexpr e s s edbyEq １ ( ZCPE ＝ ( ω)－n/Q １) j whe r e,Q andn a r eCPEc ons t an t s．
F i ３ Equ i v a l en tc i r c u i tf o rt h eSMSSi n３ ５ma s s％ g NaC ls o l u t i onwi t hv a r i ou spH
sr e cogn i z eda st hecha r a c t e r i z a Ｇ Thef a c t o rn i [ ] t i on o fun i f o rmi t f pa r ame t e r s３０ wh i ch a lways yo l i e sbe twe en０ ５and１ ０． I ta l soshowst hed i spe r Ｇ s i one f f e c tont hesur f a c er oughne s s．Whenn ＝１,
t heCPEde s c r i be sani de a lc apa c i t o r．Fo r０ ５＜n＜ , １ ０ t he CPE de s c r i be sad i s t r i bu t i ono fd i e l e c t r i c r e l axa t i ont ime si nf r equenc c e．Whenn ＝０ ５, yspa
t heCPEr ep r e s en t sa Wa rbur ewi t hd i f Ｇ gimpedanc f us i ona lcha r a c t e r．Thef i t t ed pa r ame t e r sa r el i s t ed i nTab l e３．RSi st heso l u t i onr e s i s t anc e,R１ i st he r r e spondst ot he r e s i s t anc eo ft hepa s s i vef i lm,Q１co , eudoc apa c i t anc eo ft hef i lm expr e s s edus i ngt he ps CPE１． R２i sacha r r ans f e rr e s i s t anc eo ft hep i t Ｇ get , ( ) t i ngho l e andQ２ CPE２ co r r e spondst oacha r ge t r ans f e rc apa c i t anc eo ft hep i t t i ng ho l e．F i t t i ngex Ｇ r imen t a lda t af r om F i ２a r es imu l a t edbyequ i va Ｇ pe g ２ , fva r i anc ei nTab l e３ l en tc i r cu i ta swe l la st heX o wh i cha r er e l a t i ve l l li n magn i t ude．The s er e Ｇ ysma su l t sc ande t e rmi net heequ i va l en tc i r cu i td i ag r ams mo r esu i t ab l ef o rt heexpe r imen t．Equ i va l en tc i r cu i t mode lshowst ha tpa s s i vef i lm doe sno tcomp l e t e l y cove rt heme t a lsur f a c e,wh i chduet osur f a c er oughＧ ne s sando t he rr e a sonst ha tc anc aus et hed i spe r s i on e f f e c t．Thepa s s i vef i lmi sno taun i f o rml aye r,bu ta
Tab l e３ Equ i v a l en tc i r c u i tpa r ame t e r si n３ ５ma s s％ NaC ls o l u t i onwi t hv a r i ou spHa t－０ １V S t e e lt ype andpH
RS/ ( Ωcm２)
SMSS２ Ｇ pH４
２ ０８７
SMSS１ Ｇ pH４ SMSS１ Ｇ pH１０ SMSS２ Ｇ pH１０
R１/ ( Ωcm２)
Q１/ ( F cm－２)
n１
Q２/( Fcm－２)
n２
R２/ ( Ωcm２)
X２/
１０－３
５ １３６
１ ６２５×１０
６ ４９５×１０
０ ９０６
６ ７１３×１０
０ ７２２
１ ０７３×１０
１ ９０９６
５ ３２２
３ １８２×１０５
１ ４７７×１０－５
０ ９３４
４ ０９１×１０－５
０ ８２１
１ ８３２×１０６
２ ３５５５
４ ２１１
５
１ ０３２×１０５
２ ３７７×１０５
－５
６ ８０２×１０－５
１ ９２９×１０－５
r ousf i lmo fs emi c onduc t o rcha r a c t e r i s t i c３１Ｇ３３ ． po Whens imu l a t i ngequ i va l en tc i r cu i t,t hepo l a r i Ｇ z a t i onr e s i s t anc e Rp i sde c i ded byt he R１ and R２ , name l anbes e enf r om Tab l e３, yRp＝R１ ＋R２ ．Asc , i na l ka l i necond i t i on bo t hR１ andR２i nc r e a s e swi t h
０ ９２２ ０ ９４６
－５
６ ９３４×１０－５ ２ ２１８×１０－５
０ ７７８ ０ ８１９
５
３ ０３７×１０４ ８ ８４６×１０５
２ ３１９１ ２ ８５４６
f i lm de c r e a s e s．Th i si scons i s t en twi t ht hepa s s i va Ｇ t i oncur r en tdens i t v a l u e so b t a i n e di nT a b l e２． T h e y r o t e c t i onab i l i t fpa s s i vef i lmo fs amp l eSMSS１i s p yo h i rt hant ha to fs amp l eSMSS２,a sshownbyt he ghe h i rf i lm r e s i s t anc e．Att hes amet ime,CPE１o f ghe amp l ei sl owe r． R２ o fs amp l eSMSS１i ss i Ｇ t hei nc r e a s eo fpHva l ue． Sot heRpva l uei nt hea l ka Ｇ SMSS１s g i f i c an t l i r．TheRp o fs amp l eSMSS１i smuch l i necond i t i oni sh i rt hant ha ti nt hea c i d i cc ond i Ｇ n yh ghe ghe i rt hanRp o fs amp l eSMSS２．Thepa s s i vef i lm t i on． I tshowst ha t,duet oi nc r e a s edpH,ma t e r i a l s h ghe t ruc t ur eo fs amp l eSMSS１i s mo r es t ab l e,andc a Ｇ o t e c t i onc apa c i t l lenhanc e．Thef i lm wi l lhave s pr y wi a c i t o f a s s i v e f i l mi s e n h a n c i n ． I na c i d i cN a C l s o Ｇ h i h e rs t a b i l i t a n dc o m a c t n e s sa f t e r o l a r i z a t i o n． p y p g g y p p , , u t i on whe t he rs amp l eSMSS１o rs amp l eSMSS２, I na dd i t i on n１ a ndn２ v a l u e sa r eh i na l k a l i n ec ond i Ｇ l ghi heR２ wa ssma l l e rt han R１ ．Th i sc anbeexp l a i ned t i on,wh i c hi l l us t r a t e st ha tt hepa s s i vef i lm o fs t a i n Ｇ t l e s ss t e e lf o rmedi na l ka l i nec ond i t i oni s mo r eun i Ｇ byt hef a c tt ha tt hee l e c t r o l t eso l u t i on wa spa r t l y y [ ] f o rmandcompa c t．Andt hepa s s i vef i lmi smo r es t a Ｇ sho r t Ｇ c i r cu i t edi nt hemi c r opo r e so ri n t e r s t i t i a l s３４ ． b l e,t her e Ｇ s s i va t i onab i l i t l lbeimp r oved．I n pa y wi , t hes amepHc ond i t i ons i ti sobs e r vedt ha tt heR１o f ２ ３ XPSde t hpr o f i l i ngo fSMSSs amp l e sa td i f f e r Ｇ p s amp l eSMSS２i sl e s st hant ha to fs amp l eSMSS１, en tpHc ond i t i on s i nd i c a t i ng t ha tt he c o r r o s i on r e s i s t anc eo f pa s s i ve Thr ought heana l i so fpo l a r i z a t i oncur ve sand ys [
]
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
EI S,i tp r ove st ha tt he pa s s i ve f i lm o fs amp l e SMSS１i smo r es t ab l et hant ha to fs amp l eSMSS２i n t hes ame pH c ond i t i on．Att hes amet ime,i ta l s o r ove st ha tt hepa s s i va t i onab i l i t fSMSSs amp l ei n p yo a l ka l i necond i t i oni ss t r onge rt hant ha ti na c i d i cc on Ｇ d i t i on．I no r de rt of u r t he rexp l a i nt he p r ope r t f yo s s i vef i lm, XPS dep t hp r o f i l i ng da t ao f SMSS pa s amp l e swi l lbedonei nbo t hc ond i t i ons: ( ) １ I n３ ５ ma s s％ NaClso l u t i onso fpH ４, －０ １Vv s． SCE ( l a r i z a t i ont imei s１h)． po ( ２)I n３ ５ ma s s％ NaCls o l u t i onso fpH １０, ( ) －０ １Vv s． SCE po l a r i z a t i ont imei s１h ． I nana l i so fXPSs t anda r dspe c t r a,Fee l emen t ys c o r r e spondst ot hepe akb i nd i ngene r f７０７eV, gyo ( , , , andt heFe Ｇ ox i de s FeO Fe２O３ Fe３O４ e t c )a r ei n t hev i c i n i t f７１０eV;Cre l eme n tc o r r e s st ot h e yo pond
１１６１
e akb i nd i nge n e r f５７４ ４eV,andt heCr Ｇ ox i de s p gyo (ma ) i n l OH) a n dC r O a r e i nt h ev i c Ｇ yCrO３ ,Cr( ３ ２ ３ i n i t f５７７eV． I no rde rt oge tbe s tr e su l t s,a l lt he yo dep t hp r o f i l i ng spe c t rums we r ep r oc e s s ed i nt he s ameway． Fo rexamp l e,as amp l esur f a c ei nF i ４ s g i ( ) ana l z edbyl aye rbyl aye r １nm pe rl aye rt oob t a i n y Fe ２p３/２andCr ２p３/２o r i i na lb i nd i ngene r c t rum g gyspe o fSMSS１ ( i npH４)． Fr omou t s i det oi ns i de,Feand Cra r el oc a t edi nt heh i rb i nd i ngene r akt han ghe gype t heb i nd i ngene r fe l emen t a ls t a t e,wh i chshows gyo t ha tt heox i de sf o rmi nt hepa s s i vef i lm．Wi t ht hei n Ｇ , , c r e a s eo fdep t h f r om ou t s i det oi ns i de FeandCr a r ef oundbyt he i re l emen t a ls t a t e,i nd i c a t i ngt ha ti t , ha sbe enobs e r vedwi t h i nt he i rma t r i x．The r e f o r ei t c anbeconc l udedt ha tt heox i da t i ons t a t e so fFeand Cra r ep r e s en ti nt hepa s s i vef i lm．
( a)Fe ２p３/２; ( b)Cr ２p３/２．
F i ４ En e r e c t r umo fSMSS １( i npH４)s amp l ewi t hd ep t hchang e g g ys p
Theo r i i na lXPSspe c t r aa r ef u r t h e ra n a l z e dby g y LLS ( L i ne a rLe a s tSqua r e s)way．Asa r onspu t Ｇ goni , t e r i ngdep t hchange s chemi c a ls t a t ed i s t r i bu t i onso f FeandCri nt hepa s s i vef i lm we r eob t a i nedi ntwo i t i onsf r om F i ５．Wi t ht hei nc r e a s eo f pH cond g , spu t t e r i ngdep t hc on t en t st endt obes t ab l e． Crno r Ｇ ma l l i b i t st hr e echemi c a ls t a t e si nt he pa s s i ve yexh f i lm．Whent hespu t t e r i ngdep t hi ssma l l e r,Cri sde Ｇ ( ) r i vedf r omt heCr OH ３ ．Wi t hi nc r e a s i ngt hespu t Ｇ t e r i ngdep t h,Cri sde r i vedf r om t heCr２O３ ．When t hespu t t e r i ngdep t hi sc l o s et ot hema t r i x,Cri se l e Ｇ [ ４, ３５] men t a ls t a t e ．Ac c o r d i ng t ot he me t hod men Ｇ t i onedby Gebe r t,t het h i ckne s so ft hepa s s i vef i lm c anbee s t ima t eda st hedep t h whe r et heox i dec on Ｇ t en td r opst ot he mi dva l uebe twe ent hei n i t i a land [ , ] r e s i dua loxygenc on t en t３６ ３７ ．Ac c o r d i ngt oF i ４ gs , and５ i tc anbej udgedt ha tt hesput t e r i ng dept h
( ５nmi ndep t h)c anbecons i de r eda st het h i ckne s s o fpa s s i vef i lm． Ther e a sonwhyt hepa s s i vef i lm o fFe ＧCra l l oy /Fer ha sap r o t e c t i onc apa c i t st ha tt heCr a t i oi s yi r e a t l r oved,andt he Cr Ｇ ox i dei sa p r o t e c t i ve g yimp e f f e c t i vecomponen tf o rt hepa s s i vef i lm．Theh i r ghe r a t i or e su l t si n mo r ee f f e c t i vec apa c i t f pa s s i ve yo f i lm p r even t i ng me t a lco r r os i on．TheFe Ｇ ox i deand Cr Ｇ ox i deo fa t omi cc on c e n t r a t i onr a t i oi n s i d et hed e t h p o f６nma r el i s t edi nTab l e４． Bo t hi na c i d i canda l ka Ｇ l i necond i t i ons,Cr Ｇ ox i decon t en to fs amp l eSMSS１ i sh i rt hant ha to fs amp l eSMSS２i nt hepa s s i va Ｇ ghe t i onl aye r． I nt h i st e s t,t hepa s s i vef i lmi scompos ed o fCr Ｇ ox i deand Fe Ｇ ox i del aye r s．MoOn－ i onsf r om t hepa s s i vef i lm changet heo r i i na lan i on un i t i ng g wi t hc a t i ons,p r omo t i ng O２－ i onsmi r a t i on,r e su l Ｇ g － , t i ngi nt hef o rma t i ono fCr Ｇ ox i de h i nd e r i ngC li on s
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
１１６２
( a)SMSS１i npH４; ( b)SMSS２i npH４; ( c)SMSS１i npH１０; ( d)SMSS２i npH１０．
F i ５ XPSd ep t hp r o f i l e so fpa s s i v a t e dSMSS g
Tab l e４ Fe Ｇ ox i d eandCr Ｇ ox i d ea t omi cc onc en t r a t i on si nt h er ang eo f１－６nm ma s s％ At omi cc onc en t r a t i onsi nd i f f e r en tdep t hs
Samp l e
Ox i de
SMSS１ Ｇ pH４
Fe Ｇ ox i de Cr Ｇ ox i de
７０ ７３３９ ２９ ２６６１
７６ ０２５３ ２３ ９７４７
６２ １７４７ ２４ ２４１６
３６ ０９３５ １６ ２４７０
１３ ３２７８ ７ ８８８２
５ ９２８５ ３ ２０５５
Fe Ｇ ox i de Cr Ｇ ox i de
７６ １１６１ ２３ ８８３９
７９ ９０３４ ２０ ０９６６
６４ ３５８１ ２２ ３７０４
３３ ０１７０ １４ ７８６１
１７ ５６９１ ７ ４４１０
５ ７１２１ ３ ２５５７
SMSS２ Ｇ pH４ SMSS１ Ｇ pH１０ SMSS２ Ｇ pH１０
Fe Ｇ ox i de Cr Ｇ ox i de
Fe Ｇ ox i de Cr Ｇ ox i de
１nm
６４ ７４７１ ３５ ２５２９
８２ ５３４３ １７ ４６５７
２nm
７７ １０９６ ２２ ８９０４
８５ ５２０５ １４ ４７９５
t oen t e rt hepa s s i vef i lmand mak i ngf i lm mo r es t a Ｇ [ ] b l e３８ ．Duet oCr Ｇ ox i deads o rbedont hesu r f a c e,t he o r i i na lan i on Ｇ s e l e c t i ve pa s s i vef i lm wou l d be c ome g c a t i on Ｇ s e l e c t i ve．Thus,i tc anbeexc l udedbye r o s i on － andde s t ruc t i ono fCl i onsont hepa s s i vef i lm．The s s i vef i lmc ang r e a t l r ovet hec o r r o s i onr e s i s t Ｇ pa yimp [ ] anc e３９ ．Add i ng W no ton l r ove st he pa s s i ve yimp [ ] f i lm p r ope r t fSMSS４０ bu ta l s op r omo t e s Mot o yo
３nm
５９ ５６８４ ２３ ３６８９
８２ ５９２８ １７ ４０７２
４nm
２４ １３１４ １４ ６２６８
４５ １２２６ １３ ２３６０
５nm
１４ ０９０２ ６ ６８２９
１８ ７９６１ ６ ６７５７
６nm
４ ５３２７ ３ ００９６
８ ３４３６ ２ ８７５８
４１ ４２ t r ans f o rmi n t o MoO２－ ．MoO２－ ndFe２＋ f o rm ４ ４ a FeMoO４ ,andFeMoO４ wi l lmakemo r eCr Ｇ ox i deand [, ] Fe Ｇ ox i def o rmedont hepa s s i vef i lm ４ ４３ ．Asshown /Fer i n Tab l e４,t he Cr a t i oo fs amp l e SMSS１i s , s l i t l i rt hant ha to fs amp l eSMSS２ wh i ch gh yh ghe wi l limp r ovet heb l ock i ngc apab i l i t ha tpa s s i vef i lm yt ha sbe en damaged by Cl－ i ons．I ti l l us t r a t e st ha t ( ) r o t e c t i o no f s a m l eS M S S １ W c o n t a i n i n i sb e t Ｇ p p g [ , ]
I s sue１２ Pa s s i v a t i onBe h a v i o r so fSup e rMa r t e n s i t i cS t a i n l e s sS t e e li n We a kAc i d i ca nd We a kAl k a l i n eNaC lSo l u t i on s
t e rt hant ha to fs amp l eSMSS２ (Wf r e e),wh i cha r e c ons i s t en twi t he l e c t r o chemi c a lt e s tr e su l t s．
３ Conc l u s i on s
( １)I nt hes amepH c ond i t i ons,t hes t ab i l i t y and un i f o rmi t f pa s s i vef i lm o fs amp l e SMSS１ yo ( c on t a i n i ng W)a r ebe t t e rt hant ho s eo fSMSS２s amＧ , l e i n d i c a t i n t h a t t h e a s s i v a t i o na b i l i t o fs a m l e p g p y p SMSS１i ss t r onge rt hant ha to fs amp l eSMSS２．The SMSSha sas t r onge rpa s s i va t i onab i l i t na l ka l i ne yi c ond i t i ont hani na c i d i cc ond i t i on,andt he pa s s i ve f i lma l soha sabe t t e rpr o t e c t i vec apa c i t y． ( ２)Thr oughana l z i ngt heEI Sexpe r imen t a l y r e su l t sand s imu l a t i ng equ i va l en tc i r cu i td i ag r am, t hepa s s i vef i lm c an bec ons i de r edt o bea po r ous s t ruc t ur ewi t hs emi c onduc t o rcha r a c t e r i s t i c s．TheRp va l uei sh i ri na l ka l i nec ond i t i ont hani na c i d i c ghe c ond i t i on,wh i chshowst ha tSMSSp r o t e c t i onc apa c Ｇ i t senhanc ed,andt hepa s s i vef i lm ha sh i rs t a Ｇ yi ghe b i l i t ompa c t ne s sa f t e r po l a r i z a t i on．I nt he y and c s amepH cond i t i ons,t he pa s s i vef i lm s t ruc t u r eo f SMSS１i s mo r es t ab l eanddens e r．The pa s s i va t i on c apa c i t fSMSSha sbe eni nc r e a s eda c c o r d i ng l yo y． ( ３)XPSdep t hpr o f i l i ngr e su l t sno ton l on Ｇ yc f i rm t heabovec onc l us i ons,bu ta l s osugge s tt ha t add i ng W c anpr omo t e mo r eCr Ｇ ox i deandFe Ｇ ox i de f o rmedont hepa s s i vef i lm．Moand W s rg i e sc an yne r educ et hedeva s t a t i on o f Cl－ i onsont he pa s s i ve , f i lm andpr o t e c t i vec apa c i t fpa s s i vef i lmha sbe en yo imp r oved． ( ４)Thepa s s i vef i lmc ompo s i t i onsi na c i d i cand a l ka l i neso l u t i onsa r emo s t l Ｇ ox i deandCr Ｇ ox i de． yFe Thes t ruc t ur eo fpa s s i vef i lmi sa mi x t u r eo fCr Ｇ ox Ｇ i de sandFe Ｇ ox i de s． Re f e r enc e s:
[ １] A．Ko c i an,C．Don i k,M． J enko,Co r r o s． Sc i． ４９ ( ２００７)２０８３ Ｇ j ２０９８． [ ２] MF．Mon t emo r,MGS． Fe r r e i r a,NE．Hak i k i,Co r r o s． Sc i． ４２ ( ２０００)１６３５ Ｇ １６５０． [ ３] S．Mi s ch l e r,A．Voge l,HJ．Ma t h i eu,D． Lando l t,Co r r o s． Sc i． ３２ ( １９９１)９２５ Ｇ ９４４． [ ４] M． Sán c h e z,H．Mahmoud,J． So l i dS t a t eE l e c t r． １６ ( ２０１２)１１９３ Ｇ １２０２． [ ５] D N． Zou,R． L i u,J． L i,W． Zhang,D．Wang,Y．Han,J． I r on S t e e lRe s． I n t． ２１ ( ２０１４)No ６,６３０ Ｇ ６３６． [ ６] X C．Han,J．L i,KY．Zhao,W．Zhang,J．Su,J． I r onS t e e l Re s． I n t． ２０ ( ２０１３)No ５,７４ Ｇ ７９． [ ７] C O A．Ol s s on,D．La ndo l t,E l e c t r o c h im．Ac t a４８ ( ２００３)１０９３ Ｇ １１０４． [ ８] S Y．Kim,H．Kim,HS．Kwan,Ma t e r．Co r r o s．５７ ( ２００６) ８３５ Ｇ ８４２．
１１６３
[ ９] S．Haup t,HH． S t r ehb l ow,Co r r o s． Sc i． ３７ ( １９９５)４３ Ｇ ５４． [ １０] HW．Hoppe,S．Haup t,HH．S t r ehb l ow,Sur f． I n t e r f a c e Ana l． ２１ ( １９９４)５１４ Ｇ ５２５． [ １１] Ž．Pe t r ov i c,N． La ç i,M．Me t i ko š ＧHukov i c,R．Bab i c,J． So l Ｇ j i dS t a t eEl e c t r． １５ ( ２０１０)１２０１ Ｇ １２０７． [ １２] J．Di ng,L． Zhang,M． Lu,J．Wang,Z．Wen,W．Hao,App l． Sur f． Sc i． ２８９ ( ２０１４)３３ Ｇ ４１． [ １３] A．Da v o o d i,M．Pak s h i r,M．Ba b a i e e,G R．Eb r ah imi,Co r r o s． S c i． ５３ ( ２０１１)３９９ Ｇ ４０８． [ １４] E． J ame s,Conc r e t eEng． I n t． ６( ２００２)６４ Ｇ ６７． [ １５] D V．Va l,MG． S t ewa r t,S t r uc t． Sa f． ２５ ( ２００３)３４３ Ｇ ３６２． [ １６] K M．Kim,K Y．Kim,J． Powe rSou r c e s１７３ ( ２００７)９１７ Ｇ ９２４． [ １７] W． J i ang,KY．Zhao,D．Ye,J．L i,Z D．L i,J．Su,J． I r on S t e e lRe s． I n t． ２０ ( ２０１３)No ５,６１ Ｇ ６５． [ １８] D．Ye,J．L i,W． J i a ng,J．Su,K．Zh a o,Ma t e r．De s． ４１ ( ２０１２) １６ Ｇ ２２． [ Su,KY．Zhao,W． J i ang, １９] YR．L i u,D．Ye,QL．Yong,J． J． I r onS t e e lRe s． I n t． １８ ( ２０１１)No １１,６０ Ｇ ６６． [ ２０] Y F．Ch e n,J L．Luo,E l e c t r o c h im．Ac t a４４ ( １９９９)２９４７ Ｇ ２９５７． [ ２１] A． Sa a t ch i,MA．Go l o z a r,K．Ra e i s s i,J．App l．El e c t r o chem． ４０ ( ２０１０)４５７ Ｇ ４６１． [ ２２] R S．L i l l a r d,GS．Kanne r,L L．Da emen,El e c t r o ch im．Ac t a ４７ ( ２００２)２４７３ Ｇ ２４８２． [ ２３] C．Bo i s s A．Dumon t,B．No rmand,El e c t r o chem．ComＧ y,C mun． ２６ ( ２０１３)１０ Ｇ １２． [ ２４] A A．He rma s,MS．Mo r a d,Co r r o s． S c i． ５０ ( ２００８)２７１０ Ｇ ２７１７． [ ２５] B．Gu i t i án,X R．Nó v o a,B． Pug a,E l e c t r o c h im．Ac t a． ５６ ( ２０１１)
７７７２ Ｇ ７７７９． [ ao,X G．L i,App l．Sur f．Sc i． ２５８ ２６] H．Luo,C F．Dong,K．Xi ( ２０１１)６３１ Ｇ ６３９． [ ２７] V．Gu i ñón ＧP i n a,A． I a l ＧMuño z,J．Ga r c í a ＧAn t ón,Co r r o s．S c i． gu ５３ ( ２０１１)５７５ Ｇ ５８１． [ ２８] A．Ko c i an,D K．Me r l,M．J enko,Co r r o s．Sc i．５３ ( ２０１１) j ７７６ Ｇ ７８３． [ ２９] R A．An t une s,MC L．Ol i ve i r a,G．Et t,V．Et t,I n t． J．En Ｇ ( ) e r s． ３６ ２０１１ １２４７４ Ｇ １２４８５． g．Re [ ３０] A．Popova,E．Soko l ova,S．Ra i cheva,M．Chr i s t ov,Co r r o s． Sc i． ４５ ( ２００３)３３ Ｇ ５８． [ ３１] AK． I ve r s en,Co r r o s． Sc i． ４８ ( ２００６)１０３６ Ｇ １０５８． [ i,M． Zhu,J． So l i dS t a t eEl e c t r． １８ ３２] Z J． Zheng,Y．Gao,Y．Gu ( ２０１４)２２０１ Ｇ ２２１０． [ ３３] L A S．R i e s,M．DaCunh aBe l o,MG S． Fe r r e i r a,I L．Mu l l e r, Co r r o s． Sc i． ５０ ( ２００８)６７６ Ｇ ６８６． [ ３４] C．Hi t z,A．La s i a,J．El e c t r oana l．Chem． ５００ ( ２００１)２１３ Ｇ ２２２． [ ３５] C F．Chen,R J． J i ang,J S．Qi an,S Q．Zheng,Ac t aPhys． Ch im． S i n． ２５ ( ２００９)１２１３ Ｇ １２１８． [ ３６] A．Gebe r t,K． Buchho l z,A． Leonha r d,K．Mumme r t,J． Eck Ｇ e r t,L． Schu l t z,Ma t e r． Sc i．Eng．A２６７ ( １９９９)２９４ Ｇ ３００． [ ３７] MJ．Ca rme z im,A M．S imõ e s,MF．Mon t emo r,M．DaCunh a Be l o,Co r r o s． Sc i． ４７ ( ２００５)５８１ Ｇ ５９１． [ ３８] S．Naga r a an,N．Ra end r an,Co r r o s． Sc i． ５１ ( ２００９)２１７ Ｇ ２２４． j j [ ３９] YH．L i n,R G．Du,R G．Hu,C J．L i n,Ac t aPhys．Ch im． S i n． ２１ ( ２００５)７４０ Ｇ ７４５． [ ４０] A． I rhz o,Y． Segu i,N． Bu i,F．Dabo s i,Co r r o s． Sc i． ２６ ( １９８６)
７６９ Ｇ ７８０． [ ４１] J S．Kim,P J．X i a ng,K Y．Kim,Co r r o s i on６１ ( ２００５)１７４ Ｇ １８３． [ ４２] K M．Kim,J H．Kim,K Y．Kim,ECST r a n s． ２５ ( ２００９)１８２３ Ｇ １８３２． [ ４３] KH．Lo,C H．Shek,J K．L．La i,Ma t e r．Sc i．Eng．R ６５ ( ２００９)３９ Ｇ １０４．