Passive Films

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Accepted Manuscript

Facile chromaticity approach for the inspection of passive films on austenitic

stainless steel

Cong Qian Cheng, Jie Zhao, Tie Shan Cao, Qin Qin Fu, Ming Kai Lei, De Wei

Deng

PII: S0010-938X(13)00041-3

DOI: http://dx.doi.org/10.1016/j.corsci.2013.01.035

Reference: CS 5253

To appear in: Corrosion Science

Received Date: 23 November 2012Accepted Date: 19 January 2013

Please cite this article as: C.Q. Cheng, J. Zhao, T.S. Cao, Q.Q. Fu, M.K. Lei, D.W. Deng, Facile chromaticity

approach for the inspection of passive films on austenitic stainless steel, Corrosion Science(2013), doi: http://

dx.doi.org/10.1016/j.corsci.2013.01.035

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Facile chromaticity approach for the inspection of passive films on austenitic stainless steel

Cong Qian Cheng, Jie Zhao*, Tie Shan Cao, Qin Qin Fu, Ming Kai Lei, De Wei Deng

(School of Materials Science and Engineering, Dalian University of Technology, Dalian, 116085, China)

Corresponding author: Jie Zhao, Email: [email protected], Tel: 86 411 84709076, Fax: 86 411 84709284

Abstract

A chromaticity approach for the inspection of passive films on 304 stainless steel is explored by measuring the redness

degree of the colouration reaction product of phenanthroline. The measurement exhibits good capability in evaluating

film quality. The measured values are dependent on the structural integrity of the passive films. Based on the

electrochemical examination and XPS spectra, this approach is discussed from the view point of the inhibition of the

passive films on the release of ferrous from the matrix during its reaction with phenanthroline. The preferential

dissolution of Fe-rich oxides in the films can affect the measurement.

Keywords: A. stainless steel; B. cyclic voltammetry; B. XPS; B. polarisation; C. passive films.

1. Introduction

Austenitic stainless steel (ASS) is widely used as a construction material. The bilayer structure of passive films with

outer Fe-rich oxides and inner Cr-rich oxides on ASS has attracted considerable attention because of its barrier properties

in corrosion environment [13]. The quality of passive films in ASS manufacturing is important for the safe application

of ASS facilities in nuclear reactors and chemical industries. For example, surface rust or corrosion resistance

degradation occurs if passive films are damaged by an unsuitable manufacturing process. Specifically, local corrosion

and stress corrosion cracking can develop under the following service conditions after passive films are damaged by

surface scratching and contaminants. Thus, inspecting and characterising passive films are critical processes in ASS

manufacturing.


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Various inspection techniques can be applied to characterise passive films on ASS. For instance, quantitative

approaches via physical methods, such as Auger electron spectroscopy and X-ray photoelectron spectroscopy (XPS),

can reveal the chemical structure of passive films, whose quality can then be evaluated based on the inspected

information [47]. However, most physical methods require drastic experimental conditions, such as ultra-high vacuum

conditions, and very expensive or unavailable equipment. Electrochemical tests can entirely reflect the electrochemical

property of passive films on ASS.For example, electrochemical cathodic reduction and voltammetry offer quantitative

and qualitative assessments of passive films [810]. Capacitance measurements were also successfully used to determine

the semi-conductive behaviour of passive films[1113]. The intensively red-coloured ferroin, which consists of divalent

iron and phenanthroline, has been used extensively for several years for the colourimetric determination of iron and as an

oxidation-reduction indicator [14]. This fact suggests that chemical colouration reaction may become one of the potential

approaches for the convenient inspection of passive films. However, ferroin is mostly applicable as an indicator in

solution titration analysis. No research has been reported on the application of ferroin in the inspection of passive films.

Conveniently characterising passive films on a large scale using the traditional titration method with ferroin as the

indicator is difficult. When a phenanthroline solution creates contact with a scratched ASS, the colour at the scratched

region changes into red because of the formation of ferroin. The redness degree is directly correlated with the damage

degree of passive films. This phenomenon highlights a possibility to characterise film quality using the redness degree of

the ferroin indicator.

Two typical types of passive film usually grow during ASS manufacturing: the spontaneously formed films by air

exposure and the artificial films formed by chemical passivation. This study aims to elucidate an inexpensive and rapid

method, namely, chromaticity inspection, for discerning the quality of passive films. This method consists of two

procedures. The first one is the colouration reaction of phenanthroline to produce the red-coloured ferroin indicator, and

the second is the subsequent inspection of the redness degree of the formed ferroin indicator via colour measurement.


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operated with a constant pass energy of 20 eV.

3. Results

3.1 Chromaticity measurement of passive films on 304 ASS

Fig. 1 shows the colour characteristics of the optical photos during the colouration reaction of phenanthroline in the

304 ASS samples subjected to air exposure and chemical passivation in HNO3solution. The grinding procedure before

air exposure and chemical passivation results in many fine scratches. The chemical passivation shows no obvious effect

on the surface [Fig. 1(a)]. The coated sheet after 3 s of colouration reaction is shown in Fig. 1(b). A weak red circle is

observed in the sample exposed to air for 0 h, but circles with white background images are found in the samples exposed

to air for 3 h and in the samples subjected to chemical passivation. After 180 s of colouration reaction, the red-coloured

circles are revealed in the samples exposed to air for 0 and 3 h. The intensity of redness is higher in the samples exposed

to air for 0 h than in those exposed to air for 3 h. However, the colour of the test paper is still white on the samples

subjected to chemical passivation. The experimental result from Fig. 1 indicates that the colour induced by the

colouration reaction may be sensitive to the passivation conditions. Moreover, the redness degree can be utilised to

semi-quantitatively evaluate the quality of the passive films.

Colour measurement can provide an objective specification of the quality of a colour regardless of its luminance, i.e.,

as determined by its hue and its dominant wavelength. The quality of a colour for a target can be described by several

colour coordinate systems. One of the most popular systems is the CIE Lab. The CIE Lab space is based on the concept

that colours can be considered as a combination of lightness, red and green, yellow and blue. The three coordinates in the

CIE Lab space represent the lightness of the colour (L = 0 refers to black, whereas L = 100 indicates diffuse white),

wherein aindicates the position between red and green. Negative avalues indicate green, positive values indicate red,

and bis the position between yellow (bpositive) and blue (bnegative). In addition, the difference (value) between the

target and the reference can be evaluated by subtracting the background value of the reference [16]. In the current study,


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the redness difference (value) between the test paper and the national standard colour card was measured in the CIE Lab

space. The redness degree of the ferroin indicator can be characterised by a* as follows:

0*=

aia

a

(1)

where a0and aiare the redness difference between the test paper and the reference before the attachment and after the

reaction, respectively.

The redness degree (a*) corresponding to the colouration reaction in the present work is shown in Fig. 2. Results of the

preliminary experiments demonstrating the effective scope of the colouration reaction time are presented in Fig. 2(a).

When the phenanthroline solution makes contact with 304 ASS, Fe ions are released from the substrate quickly and react

with the test solution to produce red-coloured ferroin. Therefore, the measured a* value is rapidly increased within the

initial reaction period of 60 s, as shown in Fig. 2(a). After 180 s of reaction, the complexation reaction is stabilised, and

then the measured a* value is slightly increased. The a* values of the samples are in the following order: 0 h of air

exposure > 0.2 h of air exposure > 12 h of air exposure > chemical passivation in HNO3solution. This result suggests

that the complexation reaction parameter for 180 s is suited to distinguish passive films under air exposure and chemical

passivation.

The results of a* variations for the 304 ASS samples are shown in Fig. 2(b) after 180 s of colouration reaction.

Significant differences between the samples subjected to air exposure and chemical passivation are observed. The highest

measured a* value corresponds to the sample exposed to air for 0 h. The inspected a* values decrease as the thin passive

films grow during air exposure. The measured a* values in the samples exposed to air for more than 3 h are close to 2,

indicating that more passive films have formed. Compared with the samples exposed to air, the samples subjected to

chemical passivation in HNO3solution have a* values close to 0. This finding suggests that the optimum film quality can

be found in the samples subjected to chemical passivation in HNO3solution.

The chromaticity measurement response to cathodic polarisation of the samples after 48 h of air exposure and after


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chemical passivation, with and without rinsing after cathodic polarisation, is shown in Fig. 3. The a* values of the

samples subjected to chemical passivation are close to 0 after polarisation at the potential region above -0.7 V (SCE). The

measured a* values increase rapidly at potentials more negative than -0.7 V (SCE). However, a corresponding increase in

the a* values are not observed after rinsing (Fig. 3). The a* value of the samples exposed to air is approximately 1.6 after

polarisation at the potential range of -0.4 V (SCE) to -0.6 V (SCE) and then reaches approximately 17 at potentials below

-1.2 V (SCE) without rinsing. The a* value after rinsing decreases to 12, as shown in Fig. 3.

3.2 Electrochemical behaviour of the passive films and its relationship with chromaticity measurement

Cyclic voltammetry was carried out to realise the reduction reaction related to the chromaticity measurement during

cathodic polarisation. Fig. 4 shows the cyclic voltammetry curves of the 304 ASS samples after 48 h of air exposure and

after chemical passivation. The voltammogram of the 304 ASS samples exposed to air shows a reduction peak I at

approximately -0.7 V (SCE) corresponding to the reduction and dissolution of Fe2O3or FeOOH oxides during cathodic

polarisation; an anodic peak II corresponding to the oxidation of Fe to Fe2+

and Fe3+

is also found [10, 17]. The current

density of the samples subjected to chemical passivation is significantly weakened, and both peaks are nearly negligible.

This result suggests that the reduction and preferential dissolution of Fe-rich oxides occur during cathodic polarisation at

potentials below -0.7 V (SCE).

To understand the corrosion properties of 304 ASS, which is dependent on surface passive film, the electrochemical

corrosion behaviour of 304 ASS in 3.5 wt.% NaCl solution was examined. Fig. 5 shows the potentiodynamic polarisation

curves of the 304 ASS samples in 3.5 wt.% NaCl solution and highlights their calculated pitting potentials Epittingfrom the

polarisation curves corresponding to chromaticity measurement. All samples exhibit passive behaviour in the test

solution. The passive region of the samples subjected to chemical passivation is at the potential range of 0 V to 1.04 V

(SCE). At this range, the passive film becomes stable. The pitting potential Epittingis approximately 1.04 V (SCE), above

which the breakdown of the passive films likely occurs [Fig. 5(a)]. For the samples exposed to air, both the passive


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region and Epittingincrease with prolonged air exposure, whereas the passive current density decreases with prolonged air

exposure. This result indicates that the corrosion resistance can be improved by air exposure. The current density at the

extremely wide passive region after chemical passivation in HNO3 solution is the lowest, indicating the optimum

corrosion resistance of the samples. Fig. 5(b) shows the relationship between the measured a* values from Fig. 2(b) and

the calculated Epitting from the potentiodynamic polarisation curves in Fig. 5(a), which signifies the property of local

corrosion resistance. The graphs in Fig. 5(b) show that a lower value of a* gives rise to a higher local corrosion

resistance. This result may be expected because a lower value of a* and a higher value of Epittingare expected after the

growth of the passive films during air exposure, as shown in Figs. 2(b) and 5(a), respectively. The lowest value of a* and

the highest value of Epittingat 1024 mV (SCE) in the sample subjected to chemical passivation provide the optimum local

corrosion resistance of the passive films at the a* value of 0.

Mott-Schottky analysis was employed to examine the semiconductor properties of the passive film in 3.5 wt.% NaCl

solution by measuring the capacitance developed in the films as a function of the applied electrode potential. According

to Mott-Schottky theory, the doping densities of n-type and p-type semiconductors are given by [13, 18]

2

0

1 2 ( )FBD

kTE EC eAN e

= n-type (2)

2

0

1 2( )FB

A

kTE E

C eAN e

= p-type (3)

whereEis the applied potential (SCE), eis the electron charge, is the dielectric constant of the passive films, 0is the

vacuum permittivity, A is the surface area of the electrode interface, k is the Boltzman constant, T is the absolute

temperature,EFBis the flat-band potential and NDandNAare the donor density for n-type semiconductor and acceptor

density for p-type semiconductor, respectively.

Fig. 6 shows the Mott-Schottky plots of the passive films in 3.5 wt.% NaCl after air exposure and chemical passivation

in HNO3solution. The capacitance of the samples without air exposure is much higher than that after air exposure and

chemical passivation. Two linear regions are identified in the Mott-Schottky plot. One has a positive slope at the potential


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The involved chemical reaction may be formulated as follows:

2+ 2+

3phen + Fe [Fe(phen) ] (red coloured Ferroin) (5)

The Fe2+

ions, namely ferrous, and the surface passive film involved in the colouration reaction are important to the

inspection measurement. The bilayer structure of the passive films with outer Fe-rich oxides and inner Cr-rich oxides

affects the release of ferrous cations involved in the colouration reaction. Fe-rich oxides do not react with phenanthroline

solution because the measured a* value is close to 0 with the existence of outer Fe-rich oxides after chemical passivation

[Figs. 2(b) and 8]. For the samples exposed to air, the content of outer Fe-rich oxides is increased and the measured a*

value is decreased with prolonged exposure time. This finding illustrates that the growth of outer Fe-rich oxides can

inhibit the colouration reaction.

The reduction and preferential dissolution of Fe-rich oxides possibly affects the measurement. The cyclic voltammetry

curves (Fig. 4) indicates that the preferential dissolution of outer Fe-rich oxides occurs during the cathodic polarisation in

3.5% NaCl solution at potentials below -0.7 V (SCE). An increase in a*value at the cathodic potentials below -0.7 V

(SCE) (Fig. 3) indicates that the residual ferrous due to the preferential dissolution of outer Fe-rich oxides affects the

colouration reaction. Moreover, the maximum a* value at the potentials below -1.2 V (SCE) is attributed to the complete

dissolution of outer Fe-rich oxides. Although the residual ferrous that originated from the preferential dissolution

possibly increases the value of a*, the rinsing process after polarisation can relieve the influence of the residual ferrous.

Consequently, the colouration reaction is dependent on the ferrous in the presence of inner Cr-rich oxides. The value of

a* is decreased to 0 after the rinsing treatment (Fig. 3) of the samples subjected to chemical passivation. This result

indicates that the inner Cr-rich oxides can prevent the colouration reaction. Therefore, the ferrous involved in the

colouration reaction possibly comes from the matrix beneath the passive films, and the growth of both outer Fe-rich

oxides and inner Cr-rich oxides in the passive films can inhibit the colouration reaction.

A comparison between Fig. 3 and Fig. 2(b) shows that the a* values before polarisation are higher than the


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corresponding values after polarisation at potentials above -0.6 V (SCE). At the potential range of -0.4 V (SCE) to -0.6 V

(SCE), the measured a* value is approximately 1.6. This result is possibly attributed to the formation of surface oxide

during polarisation. According to the cyclic voltammetry curves (Fig. 4), the oxidation peak of Fe is approximately

-0.6 V (SCE). This finding may be attributed to the fact that the surface passive films continue to grow because of the

oxidation reaction of Fe. The formation of Fe oxides is supposed to be responsible for the decrease in a* when the

samples are polarised in 3.5% NaCl solution at potentials above -0.6 V (SCE).

4.2 Growth and structural integrity of the passive films during air exposure and chemical passivation

The structural integrity or the porosity of the passive films may play important roles during the colouration reaction

because the parameter a* informs about ferrous entering from the steel matrix through the passive films. Based on the

polarisation curves in Fig. 5, the enlargement of the passive range and the increase in Epittingreveal the protective property

and stability of the passive films. At the initial period of air exposure, Epitting linearly increases with decreasing a*

because of the growth of the passive films. No difference in a*is observed between the samples exposed to air for 36 and

240 h [Fig. 2(b)]. However, the Epittingof the two samples differs by more than 200 mV. This result highlights that the

measured a*is more sensitive to the structural integrity of the passive films compared with film thickness and chemical

structure because an intact and stable passive film can inhibit the dissolution of Fe from the matrix. The XPS spectra

demonstrate that the outer Fe-rich oxides in the passive films grow during air exposure. The decrease in a*during air

exposure proves that the structural integrity of the outer Fe-rich oxides is improved.

The chromaticity measurement after cathodic reduction is associated with the integrity of the inner Cr-rich oxides

when the surface residual ferrous is removed by the rinsing process. The XPS analysis revealed the small amount of inner

Cr-rich oxides and the very slow growth of inner oxides in the passive films during air exposure (Fig. 8 and Table 2). The

high value of a* after reduction below -0.7 V (SCE) and the following rinsing treatment (Fig. 3) indicates the localised

distribution of inner Cr-rich oxides. For the samples subjected to chemical passivation, the measured a* value is close to


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0 [Figs. 2(b) and Fig. 3]. This result suggests the high integrity of both outer Fe-rich and inner Cr-rich oxides in the

passive films. Vayer et al. [4] proposed that inner Cr-rich oxides are promoted by chemical passivation and uniformly

distributed all over the passive layer. However, they revealed that oxidised iron is concentrated in the outer layer and that

oxidised chromium is locally distributed in the inner layer of 304 ASS after air exposure. The difference in structural

integrity of the passive films revealed by the chromaticity measurement is in accordance with previous studies [4].

The Mott-Schottky plots showed the p-type and n-type semi-conductivity behaviours in the passive films at different

potential regions, as well as the various doping densities after air exposure and chemical passivation. Previous studies [12,

2224] reported that the capacitance response in the p-type and n-type regions are controlled by the inner Cr-rich oxides

and outer Fe-rich oxides in passive films, respectively, thereby suggesting the dual semiconducting properties of the films.

According to point defect theory [25, 26], doping density is an indicator of non-stoichiometric defects (vacancies or

cation interstitials) in the space charge region of passive films. A decrease in doping density indicates a depletion in

defects [2227]. Therefore, the evolution of porosity and point defects in the passive films during air exposure and

chemical passivation can be revealed by the relationship between a*value and doping density. The fact that the donor

density decreases with decreasing a* value during air exposure suggests that both porosity and point defects are

decreased and hence more protective. The optimum structural integrity of the passive films can be expected from the

minimum doping densities and value of a*after chemical passivation.

5. Conclusion

(1) Based on the chromaticity characterisation of passive films after air exposure and chemical passivation, the redness

degree of ferroin produced from the colouration reaction decreases with increasing passive film quality. The value of a*,

which represents the redness degree of colour measurement, decreases with prolonged air exposure, and the minimum

value of a* is found in the samples subjected to chemical passivation.

(2) According to cyclic voltammetry and cathodic polarisation, the colouration reaction during chromaticity


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measurement can be affected by the cathodic potentials. At the potential region above -0.6 V (SCE), the reaction is

dependent on the released ferrous from the 304 ASS matrix under the inhibition of both outer Fe-rich oxides and inner

Cr-rich oxides in the passive films. At the potential region below -0.7 V (SCE), the preferential dissolution of outer

Fe-rich oxides can also affect the reaction, and inner Cr-rich oxides in the passive films are critical for the measurement.

(3) Based on the electrochemical behaviour and XPS spectra, the corrosion resistance increases with decreasing a*

value, and the donor density decreases because of the growth of outer Fe-rich oxides in the passive films during air

exposure. The best corrosion resistance of the samples after chemical passivation and the rapid increase in acceptor

density at the region of a*< 2 may be attributed to the high ratio of Cr/Fe in oxides and the high structural integrity of the

passive films.


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Acknowledgements

This work is supported by National Basic Research Program of China (2009CB724305) and National Nature Science

Foundation of China (51101024).


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References:

[1] C.O.A. Olsson, D. Landolt, Passive films on stainless steels-chemistry, structure and growth Electrochim. Acta 48

(2003) 1093-1104.

[2] D.D Macdonald, M.A. Rifaie, G.R. Engelhardt, New rate laws for the growth and reduction of passive films, J.

Electrochem Soc. 148(2001) B343-B347.

[3] G.T. Burstein, B.T. Daymond, The remarkable passivity of austenitic stainless steel in sulphuric acid solution and the

effect of repetitive temperature cycling Corros. Sci. 51(2009) 2249-2252.

[4] M. Vayer, I. Reynaud, R. Erre, XPS characterisations of passive films formed on martensitic stainless steel:

qualitative and quantitative investigations, J. Mater. Sci. 35(2000) 2581-2587.

[5] G. Lorang, M.D.C. Belo, A.M.P. Simoes, M.G.S. Ferreira, Chemical Composition of Passive Films on AISI 304

Stainless Steel, J. Electrochem. Soc. 141(1994)3347-3356.

[6] D. Wallinder, J. Pan, C. Leygraf, A. Delblance-Bauer, EIS and XPS study of surface modification of 316LVM

stainless steel after passivation, Corros. Sci. 41(1999) 275-289.

[7] N. Padhy, S.Ningshen, U.K. Mudali, B. Raj, In situ surface investigation of austenitic stainless steel in nitric acid

medium using electrochemical atomic force microscopy, Script. Mater. 62(2010) 45-48.

[8] A. Kocijam, C. Donik, M. Jenko, Electrochemical and XPS studies of the passive film formed on stainless steels in

borate buffer and chloride solutions, Corros. Sci. 49(2007) 2083-2098.

[9] Y.Y. Su, C.C. Shih, L.C. Chen, C.M. Shih, S.J. Lin, Characterization of oxide structures on stainless steel sternal

wires by electrochemical reduction, Appl. Surf. Sci. 258(2012) 2869-2875.

[10] N. Ramasubramanian, N. Preocanin, R. D. Davidson, Analysis of Passive Films on Stainless Steel by Cyclic

Voltammetry and Auger Spectroscopy, J. Electrochem. Soc. 132(1985) 793-798.

[11] N.E. Hakiki, Comparative study of structural and semiconducting properties of passive films and thermally grown


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17

oxides on AISI 304 stainless steel, Corros. Sci. 53 (2011) 2688-2699.

[12] Z. Feng, X. Cheng, C. Dong, L. Xu, X. Li, Passivity of 316L stainless steel in borate buffer solution studied by

Mott-Schottky nalysis, atomic absorption spectrometry and X-ray photoelectron spectroscopy, Corros. Sci. 52 (2010)

3646-3653.

[13] H. Sun, X.Q. Wu, E.H. Han, Influences of temperature on the oxide film properties of 304 stainless steel in high

temperature lithium borate buffer solution, Corros. Sci. 51(2009)2840-2847.

[14] T.S. Lee, I.M. Kolthoff, D.L. Leussing, Reaction of Ferrous and Ferric Iron with 1,10-Phenanthroline. I.

Dissociation Constants of Ferrous and Ferric Phenanthroline, J. Am. Chem. Soc., 70(1948) 2348-2352.

[15] R. Jung, H. Tsuchiya, S. Fujimoto, XPS characterization of passive films formed on Type 304 stainless steel in

humid atmosphere, Corros. Sci. 58 (2012) 62-68.

[16] M. L. Gietl, H.W. Schmidt, R. Giesa, A. Terrenoire, R. Balkb, Semiquantitative method for the evaluation of grease

barrier coatings, Prog. Org. Coat. 66 (2009) 107-112.

[17] N.L. Bozec, C. Compere, M. LHer, A. Laouenan, D. Costa, P. Marcus, Influence of stainless steel surface treatment

on the oxygen reduction reaction in seawater, Corros. Sci. 43(2001) 765-786.

[18] I. Nici, D.D. Macdonald, The passivity of type 316L stainless steel in borate buffer solution, J. Nucl. Mater.

379(2008)54-58.

[19] D. Mandrino, C. Donik, Chemical-state information obtained by AES and XPS from thin oxide layers on duplex

stainless steel surfaces, Vacuum 86 (2011) 18-22.

[20] Y. Boudevilie, F. Figueras, M. Forissier, J. Portefaix, J. C Vedrine, Correlations between X-ray photoelectron

spectroscopy data and catalytic properties in selective oxidation on Sb Sn O catalysts, J. Catal., 58 (1979) 52-60.

[21] Scofield J. H., Hartree-slater subshell photoionization cross-sections at 1254 and 1487 eV, J. Elec. Spec., 8 (1976)

129-137.


19/34

18

[22] S. Ningshena, U. Kamachi Mudalia, V.K. Mittalb, H.S. Khatak, Semiconducting and passive film properties of

nitrogen-containing type 316LN stainless steels, Corros. Sci. 49(2007) 481-496.

[23] K. Azumi, T. Ohtsuka, N. Sato, Mott-Schottky plot of the passive film formed on iron in neutral borate and

phosphate solutions, J. Electrochem. Soc. 134 (1987) 1352-1357.

[24] L. Hamadou, A. Kadri, N. Benbrahim, J-P. Petit, Characterization of thin anodically grown oxide films on AISI

304L stainless steel, J. Electrochem. Soc. 154 (1987) G291-G297.

[25] M. Kamrunnahar, J. Bao, D.D. Macdonald, Challenges in the theory of electron transfer at passive interfaces, Corros.

Sci. 47(2005) 3111-3139.

[26] A. Fattah-alhosseini, F. Soltani, F. Shirsalimi, B. Ezadi, N. Attarzadeh, The semiconducting properties of passive

films formed on AISI 316L and AISI 321 stainless steel: A test of the point defect model (PDM), Corros. Sci.

53(2011) 3186-3192.

[27] C.A. Della Rovere, J.H. Alano, R.Silva, P.A.P. Nascente, J.Otubo, S.E. Kuri, Characterization of passive films on

shape memory stainless steels. Corros. Sci. 57(2012) 154-161.


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Figure captions

Fig.1 Optical photograph during colouration reaction of phenanthroline solution with 304 ASS samples after air exposure

and chemical passivation in HNO3solution: (a) before colouration reaction, (b) after colouration reaction for 3 s, (c) after

colouration reaction for 180 s.

Fig. 2 Colour measurement after colouration reaction of phenanthroline solution with 304 ASS samples after air exposure

and chemical passivation in HNO3solution: (a) value of a* measured at different colouration reaction time, (b) value of

a* after colouration reaction for 180 s.

Fig. 3 Chromaticity measurements under various cathodic reduction conditions for 304 ASS after air exposure for 48 hr

(Sair-48 hr) and that after chemical passivation in HNO3solution (Scp).

Fig. 4 Cyclic voltammetry curves for 304 ASS in 3.5 % NaCl solution at a sweep rate of 50 mV/s after various

passivation treatment: (a) after air exposure for 48 hr and the sequence of cycles at the selected area of peak I (top insert),

(b) after chemical passivation in HNO3solution.

Fig. 5 (a) Potentiodynamic polarisation curves in 3.5 % NaCl solution for 304 ASS after air exposure and chemical

passivation in HNO3solution, (b) relationship between the value of a* in Fig. 2(b) and the Epittingcalculated from Fig.

3(a).

Fig. 6 Mott-Schottky plots of passive film in 3.5 wt. % NaCl solution for 304 ASS after air exposure and chemical

passivation in HNO3solution.

Fig. 7 Relationship between values of measured a* and the calculated doping densities in Tab. 1

Fig. 8 XPS spectra Cr 2p3/2, Fe 2p3/2, and O 1s detected for passive films on 304 ASS after air exposure and chemical

passivation in HNO3solution: (a) Cr 2p3/2, (b) Fe 2p3/2, (c) O 1s.


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Tab. 1 Calculated doping densities in passive films on 304 ASS after air exposure and chemical passivation in HNO 3

solution.

Tab. 2 Relative atomic concentration calculated from XPS spectra for 304 ASS after air exposure and chemical

passivation in HNO3solution.


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Tab. 1

Air exposure

0 hr 1 hr 12 hr

Chemical passivation

ND(1021

cm-3

) 3.56 2.68 1.75 1.7

NA(1021

cm-3

) 4.37 4.51 4.29 1.9


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22

Tab. 2

Air exposure

Relative atomic concentration

0 hr 1 hr 12 hr

Chemical

passivation

{[Crox]+[Crhyd]}/ {[Crox]+[Crhyd]+[Crmet]} 0.81 0.83 0.85 0.92

{[Feox]+ [Fehyd]}/{ [Feox]+ [Fehyd]+[Femet]} 0.78 0.77 0.88 0.71

{[Crox]+[Crhyd]}/ {[Feox]+ [Fehyd]} 0.5 0.6 0.4 1.86

[O2-

]/ [OH-] 0.5 0.4 0.4 0.7


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23

Fig. 1


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25

Fig. 3


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26

Fig. 4


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27

Fig. 5


29/34

28

Fig. 6


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29

Fig. 7


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30

Fig. 8

Fig. 8 (a)


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31

Fig. 8(b)


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32

Fig. 8(c)


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Documents

Passive Films