- Email: [email protected]
An XPS study of passive film formation on Fe30Mn9Al alloy in sodium sulphate solution
‘.‘.‘.‘.“~:.:.:x .>I (j .:::. :::>~.::.:y.:..:, ::::.g::,., _~,.::~:.:.:i:~.::::::..:.:l:.:i~,:: ,....... ,\.. .,., ,,,.,,,, i 2,: ,.... :....A
applied
surface science ELSEVIER
Applied Surface Science 115 (1998)
I I-16
An XPS study of passive film formation on Fe-3OMn-9Al in sodium sulphate solution
alloy
X.M. Zhu *, Y.S. Zhang Received
I3 March 1997; accepted
I I September 1997
Abstract The passive film formed on the surface of the Fe-30Mn-9Al alloy in I M sodium sulphate (Na,SO,) aqueous solution has been studied by X-ray photo-electron spectroscopy. The results of depth-concentration profiles analysis suggest that the passive film consists of bound water, hydroxyl species, Fe’+ hydroxide. oxides of Fe”+ and Fe”, oxides of Mn”+ and Mn”+, A13+ hydroxide and Al’+ oxide. The passive film is probably hydrous. It seems that there is a transition layer constituting of the low valent oxides and the metallic elements between the passive film and alloy matrix. 0 1998 Elsevier Science B.V.
1. Introduction In the past decade, the development of Fe-Mn-Al alloys as a substitute for conventional Fe-Cr-Ni stainless steels has been a subject of interest to many materials scientists [1,2]. There are numerous studies on the electrochemical corrosion properties of Fe(28-3lwt%)Mn-(7-lOwt%)Al alloys [3-l I]. With regards to the possibility of developing Fe-Mn-Al alloys to substitute for stainless steels, there are conflicting results about their corrosion resistance in aqueous solutions. Wang and Beck [3] reported that the corrosion rate in artificial seawater of Fe-30MnlOAl-1Si alloy was somewhat lower than that of AISI 321 stainless steel on the basis of potentiodynamic measurement and test of immersion in natural seawater. In another article, Wang and Rapp [4] also showed that the ferritic Fe-Mn-Al alloys were gen-
. Corresponding author. [email protected].
Fax:
+ 86-411-4606139:
e-mail:
0169~3332/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved PII SOI 69-4332(97)00409I
erally superior to the Fe- 1OCr steel in both seawater and I N H,SO, solution. On the contrary, other works [5-l I] have found that the corrosion resistance of examined Fe-Mn-Al alloys in aqueous solution was inferior to that for austenitic Fe-Cr-Ni stainless steels. Recently, the effect of biphase on corrosion and sensitivities to environmentally assisted cracking of Fe-Mn-Al alloys in 3.5% NaCl solution has been reported [5,6]. However. the studies mentioned above only consider the anodic polarization or immersion tests. In order to obtain further information about the possibility of substituting conventional stainless steels by Fe-Mn-Al alloys, it is needed to study the configuration of passive film formed on Fe-Mn-Al alloys. As we know, X-ray photo-electron spectroscopy (XPS) has become extremely effective in assessing the chemistry and structure of passive films. There is increasing evidence that even the hydrates can be at least partly preserved in the vacuum chamber of spectrometer. Therefore, in the present study, the XPS depth-con-
12
X.M. Zhu. Y.S. Zhmg/Applied
Surface Science 125 (19981 II-16
centration profiles were performed for the passive film formed on a Fe-30Mn-9Al alloy in sodium sulphate (Na, SO,) solution.
2. Experimental
procedures
The experimental alloy was prepared from lowcarbon iron, electrolytic manganese and industrial pure aluminium by induction furnace melting under an argon atmosphere of about 1 bar. The analysed compositions of the alloy tested are given in Table 1. The ingot was homogenized for 2 h at 1423 K, and was hot forged into 20 mm X 20 mm bars, specimens with 5 mm X 10 mm X 2 mm were machined from the bars solution treated for 1 h at 1273 K and then water-cooled. The structure of the experimental alloy as detected by X-ray diffraction is single austenite phase. Samples were first wet ground with 800 grit silicon carbide paper and then with diamond paste ( _ 1.5 pm), washed in distilled water and rinsed in acetone prior to passivation. The surface in contact with the electrolyte was 0.5 cm’. The test solution (1 M Na,SO,) was made from analytical grade reagent and distilled water. Electrochemical polarization curve and passive film were obtained by using a PAR 351 model galvanostat/potentiostat with a conventional three-electrode cell. Before passivation, the air-formed oxides on mechanically polished surfaces of specimens were dissolved by cathodic reduction for 5 min at - 850 mV and then held at a constant passive potential of 580 mV corresponding to the median passive region of alloy for 15 min in Na,SO, solution. The surface film formed on passivated sample of Fe-30Mn-9Al alloy was colourless. Fig. 1 illustrates the polarization curve, and the passive potential is marked in the figure. XPS spectra measurements were performed with a LAS-3000 combined XPS/AES/SIMS surface analysis system using a Al K a radiation (hv = 1486.6
Table I Analysed
compositions
(wt%X) of the steel tested
C
Mn
Al
Si
Fe
0.90
30.2
9.22
0.06
balance
-I?001 IV
I
I
IV
10”
I IO’
I
I
IO’
IO’
I IOJ
( IO’
IO”
, Fig. 1. Polarization solution.
curve of Fe-30Mn-9Al
alloy in 1 M Na,SO,
eV). The background pressure in the sample chamber was about 2 X 10m9 Torr. The energy of the primary electron beam and the Ar+ sputtering beam are 3 and 2.5 keV, respectively. The sputtering rate was calibrated to be 2.5 i min-’ by ion etching of a Ta sample covered with Ta,O, film of known thickness. However, the sputtering depths are reported without correction for possible difference in sputtering yield between the passive film and TazO, reference oxide. The binding energies of the oxide and metallic states of Fe2p, Mn2p, A12p and 01 s were referred to the elemental carbon 1s line at 284.6 eV, recorded from graphite. The obtained XPS spectra were fitted by using a convoluted GaussianLorentzian line shape after removing the Shirley background [ 12-J.
3. Results and discussion The XPS depth-concentration profiles for the passive film formed on Fe-30Mn-9Al alloy in 1 M Na, SO, solution at 580 mV (SCE) were determined. Fig. 2 shows the XPS spectra of outermost surface for the passive film formed on Fe-30Mn-9Al alloy. The 01s peak is fitted into three components. The peak with a binding energy of 530.58 eV is at-
X.M. Zhu. Y.S. Zhang/Applied
13
Surface Science 125 (1998) 11-16
1800
50
200 0 707
702
712
717
Binding 600
722
0
727
732
631
636
641
646
656
651
661
Binding energy (eV)
energy (eV) 12000
[
r
10000
500
400
300
200
2000
100
0
69
70
71
72
73
74
75
76
77
78
n -525
79
527
529
XPS spectra for the passive
533
535
537
Binding energy (eV)
Binding energy (eV) Fig. 2. Computer-fitted sputtering.
531
film of Fe-30Mn-9Al
tributed to O’- (or M-O bonds), while the peak at 532 eV is assigned to OH- (or M-OH bonds) and the peak at 533.28 eV to H,O (bound water). From the reported work [ 131, the 01s line (about 530 eV) has been used extensively in the analysis of oxide surface species. Differences between hydroxyl oxygen (OH-) and oxide oxygen are usually recognized by an 01s shift of l- 1.5 eV. Bonding of water molecules in different surface configurations appar-
alloy formed
in
I M Na,SO,
at 580 mV (SCE), prior to
ently cause binding energy shifts about a 3 eV range. The Fe2p,,? peak at a binding energy of 724.56 eV and the Fe’tp,,, peak at a binding energy of 7 11.2 eV are due to an Fe3+ hydroxide. The Mn2p line is fitted into two components. The Mn2p,,2 peaks at a binding energy of 654.33 eV and 652.53 eV and the Mn2p,,, peaks at a binding energy of 642.37 eV and 640.96 eV are attributed to the presence of MnO, and MnO, respectively. There are two promi-
nent satellite peaks located between Mn2p,,? peak and Mn2p,,, peak. The Al,, line is split into two peaks of 75.28 eV and 74.18 eV representing A13+ hydroxide and Al’+ oxide, respectively. The transitions in binding energy and valence state of 0. Fe, Mn, and Al which obtained from XPS depth-concentration profiles are listed in Table 2. The 01s peaks at binding energy of 530.38 to 530.60 eV, 531.44 to 532.00 eV and 532.48 to 532.74 eV are corresponding to oxygen in oxides of Fe and Mn, in hydroxide and oxide of Al and in H,O, respectively. The fitted bind energy values of Fe2p,,?, and A12p in XPS spectra of the passive Mn2p,/? film correspond to the chemical valent states of Fe3+, Fe’+ and Fe”. MnJ+, Mn’+, Mn’+ and Mn” and Al”’ and Al’, which are due to the presence of
Table 2 Effect of sputtering Na,SO, solution
on the transition
of valence
Fe,O,, Fe0 and metallic Fe. MnO,, MnO, Mn,O, and metallic Mn, AI(O Al,O, and metallic Al in passive film, respectively. It is- difficult to differentiate between y-Fe,O,, a-Fe,O, (or their hydrates) or Fe,O, on the basis of XPS. The sputter-depth profiling showed that0 iron hydroxide disappear after sputtering for 10 A. The Fe’+ hydroxide was likely transformed into Fe3+ oxide. If Fe”+ hydroxide is reduced to Fe3+ oxide by preferential sputtering of oxygen, the presentation of Fe3+ oxide after the first sputtering may be a false artifact. However, two facts show that there is probably really a rej+ oxide in the layer of film after sputtering 10 A: (1) The affect of chemical alteration by ion bombardment, if existing, was a systematic disturbance which will not only disturbs the layer of sputtering 10 i and Fe”+
state of Fe?p. Mn2p. Al2p and 01s peaks for Fe-30Mn-9Al
Mn
Al
alloy passivated
in
0
Sputtering
Fe
depth(A)
Intensity (counts)
2p,),?
vs
Intemity kounts)
2p3,?
VS
Intemity (county)
7-p
VS
Intenhity (counts)
lb
vs
0
1737
711.20
Fe’+-hy
225 721
642.37 630.96
Mn’+-ox MI?+-ox
340 322
75.28 74.18
Al’+-hy Al’+-ox
IO
5047
710.35
Fe’+-ox
Al”-hy Al’+-ox
710.31
Fe”-ox
525 655
75.05 74.1
Al’+-hy Al’+-ox
35
5689
710.18
Fe’+-ox
159 663
74.88 73.98
Al’+-hy Al’+-ox
45
6395
710.33
Fe3’-ox
389 668
75.08 74.28
Al’+-hy Al’+-ox
75
5821 3533
710.16 707.42
Fe’+-ox Fe”
61 I 389
71.88 74.01
Al’+-hy Al’+-ox
175
5655 7490
709.86 707.12
Fe?+-ox Fe”
Mn’+-ox Mn’+-ox Mn” Mn’+-ox Mn’+-ox Mu” Mn”-ox Mn’+-ox Mn” Mn’+-ox Mn’+-ox Mn” Mn’+-ox MI?+-ox Mn” Mn’+-ox Mn”
74.88 73.98
6102
642.54 640.78 638.26 642.65 641.10 638.69 642.30 640.77 637.94 632.59 641.13 638.03 642.69 640.99 639. I I 631.67 638.97
594 653
20
496 509 51 127 625 I61 767 525 I02 618 913 73 1008 IO68 417 2161 890
127 191
74.88 74.01
Al’+-hy Al’ +-OX
I75
5626 13542
709.41 707.01
Fe’+-ox Fe”
2120 232 I
641.48 638.83
Mn’+-ox Mn”
620 40
74.50 72.23
Al’+-ox Al”
237
30 500
707.03
Fe’
8750
638.93
Mu”
427 136
74.40 72.28
Al’+-ox Al”
5592 8962 3722 3520 8372 8606 3016 7944 8604 2365 81 19 8300 2871 1654 8319 1538 6298 7159 3379 6203 6535 1464 4414 4715 1056 3195 2833
533.28 532.00 530.58 ___. 5-i? 74 53 I .58 530.43 532.58 53 I .53 530.18 532.67 531.52 530.43 532.58 531.58 530.60 532.53 53 I .5-I 530.58 532.48 53 I .44 530.37 532.53 53 I .48 530.47 532.63 53 I .45 530.38
H,O M-OH M-O H,O M-OH M-O H-0 M-OH M-O H,O M-OH M-O Hz0 M-OH M-O H,O M-OH M-0 H10 M-OH M-O Hz0 M-OH M-O H,O M-OH M-O
VS = valence state: ox = oxide: hy = hydrate.
I M
X.M. Zhu, Y.S. Zhang /Applied Surface Science 125 ( 1998) I I-16
hydroxide but also the others layers and A13+ hydroxide as well as Mn3+ oxide after the first sputtering. From the Table 2, the intensity of Mn”+ oxide and A13+ hydroxide increased about twice after the first sputtering, and this means that the reduction of ion bombardment on Mn’+ oxide and A13+ hydroxide is small or tolerable. (2) On the basis of most studies on passive film, in general, the thinner Fe’+ hydroxide is present on the outer surface of the passive film while the Fe3+ oxide is located in the inner part. With increased sputtering depth, the intensity of oxygen peak in H,O decreases, the and A12p peaks shift toward low Fe2p,,zY Mn2p,,, bind energy and the valent states show a transition from Fe3+ to Fe’+ and to Fe’, from Mn’+ to Mn3+ to Mn’+ and to Mn” and from A13+-hydroxide to A13+-oxide and to Al0 while the contributions from underlying Fe’, MnO and Al0 increase. From the XPS depth profile analysis, it is likely that the passive film of Fe-30Mn-9Al alloy is much thicker than that of conventional stainless steels, and there seems to be a transition layer consisted of low valent oxides and the metallic elements between the passive film and the alloy matrix. It should be noted that the valence states of oxides are not easy to determine exactly by XPS owing to the superposition of the Fe’+ (709.3-710.7 eV) and Fe3+ (710.3-711.5 eV) peaks, the Mn’+ (640.4-641.5 eV1, Mn”+ (641.2641.7 eV> and Mn” (641.6-642.8 eVI peaks as well as the presence of satellite peaks. As show in Fig. 2 and Table 2, the passive film formed on Fe-30Mn-9Al alloy in Na,SO, solution contains H,O which is prevalent at the outer surface but which is also contained in bulk of the film. This information is consistent with the results of previous investigation which have used XPS and SIMS data to show that water is present in the passive film on iron [14]. There is disagreement, however. as to whether bound water is contained in the outermost surface alone [15] or in the bulk of the passive film as well [ 161. The present results of XPS analysis tend to support the models based on the existence of bound water in the passive film. The results shown in Fig. 2 and Table 2 suggest that the passive film consisted of bound water, hydroxyl species, hydroxide of AI and Fe and oxides of Fe, Mn and Al. It is noteworthy that the presence of bound water and the hydroxyl species existing 237 A into the passive film
15
may play an important role in improving its passivity, mainly by inducing formation of an amorphous film structure [ 141. The electrochemical corrosion resistance is probably imparted by a barrier film of bound water, hydroxides and oxides of Fe and Al, while the Mn oxides in passive film reduce the resistance to electrochemical corrosion because of its fragile and instable structure. The adverse effect of Mn in Fe-Mn-Al alloys was also recognized by noting an increase in corrosion current density and a decrease in corrosion potential in 1 M Na,SO, solution [17]. Manganese is one of the most important austenite-stabilizing elements in alloys, which not only affects the structure of alloys, but also influences the surface properties such as the formation of passive film under the electrochemical polarization. The development of Fe-Mn-Al alloys involves a compromise between economical consideration and corrosion resistance, because the manganese tends to degrade passivity of the alloys.
4. Conclusions XPS studies on the passive film formed on Fe30Mn-9Al alloy in 1 M Na:SO, solution indicate that: ( 1) The broad envelops of 01 s consist of bound water, M-OH and M-O bonds contributions. (2) Iron is present in the passive film as Fe3+ hydroxide, oxides of Fe3+ and Fe’+ and metallic Fe, manganese as oxides of MnJ’ and Mn’+ and metallic Mn and aluminum as Al’+ hydroxide, A13+ oxide and metallic Al. (3) Bound water is present in the passive film. (4) It is difficult to substitute the Fe-Mn-Al alloys for the conventional stainless steel due mainly to the presence of instable manganes oxides in the passive film of Fe-Mn-Al alloy.
Acknowledgements This project has been supported by the National Natural Science Foundation of China under Grant 59471027 and the State Key Laboratory for Corrosion and Protection of Metals. We would like to thank Profs. Cao Chunan, Lin Haichao and Wang
16
X.M. Zlzu. Y.S. Zhang / Applied Surjace Science 125 ( 1998) I I - 16
Wenhao, Mrs. Sun Yuzhen and Mr. Gong Yandong for their technical support.
References [I] S.K.
Banerji. Met. Prog. 113 (1978) 59. [2] J.C. Garcia, N. Rosas, R.T. Rioja, Met. Prog. 122 (1982) 47. [3] R. Wang, F.H. Beck, Met. Prog. 123 (1983) 72. [4] R. Wang, R.A. Rapp, in: Proc. 9th Int. Corrosion Cong.. Toronto, Canada. June 1984, Vol. 4, p. 545. [5] M. RuSEBk, T.P. Pemg, Corrosion 52 (1996) 464. [6] S.C. Chang, J.Y. Liu, H.K. Juang, Corrosion 51 (1995) 399. [7] M. Cavallini. F. Felli. R. Fratesi. F. Veniali, Werkst. Korros. 33 (1982) 281.
[S] C.J.
[9] [IO] [ll] [I21 [ 131 [14] [15] [16] [17]
Altstetter. A.P. Bentley. J.W. Fourk, A.N. Kirkbrid. Mater. Sci. Eng. 82 (1986) 13. S.C. Tjong. Surf’. Coat. Technol. 28 (1986) 181. T. Wen, B. Jing, T. Ju. J. Mater. Sci. 22 (1987) 3517. S.T. Shin, C.Y. Tai, T.P. Perng, Corrosion 49 (1993) 130. Y. Gong, Acta Met. Sinica 32 (1996) 219. D. Briggs. M.P. Seah, in: Practical Surface Analysis, 2nd ed., Wiley. New York. 1990. T.E. Pou. O.J. Murphy, V. Young, J.OM. Bockris. L.L. Tongson, Electrochem. Sot. 131 (1984) 1243. S.C. Tjong, E. Yeager. J. Electrochem. Sot. 128 (1981) 2251. O.J. Murphy, J.O’M. Bockris, T.E. Pou. D.L. Cocke, G. Sparrow. J. Electrochem. Sot. 129 (1982) 2149. X.M. Zhu. Corros. Sci. Protect. Technol. 8 (1996) 36.
applied
surface science ELSEVIER
Applied Surface Science 115 (1998)
I I-16
An XPS study of passive film formation on Fe-3OMn-9Al in sodium sulphate solution
alloy
X.M. Zhu *, Y.S. Zhang Received
I3 March 1997; accepted
I I September 1997
Abstract The passive film formed on the surface of the Fe-30Mn-9Al alloy in I M sodium sulphate (Na,SO,) aqueous solution has been studied by X-ray photo-electron spectroscopy. The results of depth-concentration profiles analysis suggest that the passive film consists of bound water, hydroxyl species, Fe’+ hydroxide. oxides of Fe”+ and Fe”, oxides of Mn”+ and Mn”+, A13+ hydroxide and Al’+ oxide. The passive film is probably hydrous. It seems that there is a transition layer constituting of the low valent oxides and the metallic elements between the passive film and alloy matrix. 0 1998 Elsevier Science B.V.
1. Introduction In the past decade, the development of Fe-Mn-Al alloys as a substitute for conventional Fe-Cr-Ni stainless steels has been a subject of interest to many materials scientists [1,2]. There are numerous studies on the electrochemical corrosion properties of Fe(28-3lwt%)Mn-(7-lOwt%)Al alloys [3-l I]. With regards to the possibility of developing Fe-Mn-Al alloys to substitute for stainless steels, there are conflicting results about their corrosion resistance in aqueous solutions. Wang and Beck [3] reported that the corrosion rate in artificial seawater of Fe-30MnlOAl-1Si alloy was somewhat lower than that of AISI 321 stainless steel on the basis of potentiodynamic measurement and test of immersion in natural seawater. In another article, Wang and Rapp [4] also showed that the ferritic Fe-Mn-Al alloys were gen-
. Corresponding author. [email protected].
Fax:
+ 86-411-4606139:
e-mail:
0169~3332/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved PII SOI 69-4332(97)00409I
erally superior to the Fe- 1OCr steel in both seawater and I N H,SO, solution. On the contrary, other works [5-l I] have found that the corrosion resistance of examined Fe-Mn-Al alloys in aqueous solution was inferior to that for austenitic Fe-Cr-Ni stainless steels. Recently, the effect of biphase on corrosion and sensitivities to environmentally assisted cracking of Fe-Mn-Al alloys in 3.5% NaCl solution has been reported [5,6]. However. the studies mentioned above only consider the anodic polarization or immersion tests. In order to obtain further information about the possibility of substituting conventional stainless steels by Fe-Mn-Al alloys, it is needed to study the configuration of passive film formed on Fe-Mn-Al alloys. As we know, X-ray photo-electron spectroscopy (XPS) has become extremely effective in assessing the chemistry and structure of passive films. There is increasing evidence that even the hydrates can be at least partly preserved in the vacuum chamber of spectrometer. Therefore, in the present study, the XPS depth-con-
12
X.M. Zhu. Y.S. Zhmg/Applied
Surface Science 125 (19981 II-16
centration profiles were performed for the passive film formed on a Fe-30Mn-9Al alloy in sodium sulphate (Na, SO,) solution.
2. Experimental
procedures
The experimental alloy was prepared from lowcarbon iron, electrolytic manganese and industrial pure aluminium by induction furnace melting under an argon atmosphere of about 1 bar. The analysed compositions of the alloy tested are given in Table 1. The ingot was homogenized for 2 h at 1423 K, and was hot forged into 20 mm X 20 mm bars, specimens with 5 mm X 10 mm X 2 mm were machined from the bars solution treated for 1 h at 1273 K and then water-cooled. The structure of the experimental alloy as detected by X-ray diffraction is single austenite phase. Samples were first wet ground with 800 grit silicon carbide paper and then with diamond paste ( _ 1.5 pm), washed in distilled water and rinsed in acetone prior to passivation. The surface in contact with the electrolyte was 0.5 cm’. The test solution (1 M Na,SO,) was made from analytical grade reagent and distilled water. Electrochemical polarization curve and passive film were obtained by using a PAR 351 model galvanostat/potentiostat with a conventional three-electrode cell. Before passivation, the air-formed oxides on mechanically polished surfaces of specimens were dissolved by cathodic reduction for 5 min at - 850 mV and then held at a constant passive potential of 580 mV corresponding to the median passive region of alloy for 15 min in Na,SO, solution. The surface film formed on passivated sample of Fe-30Mn-9Al alloy was colourless. Fig. 1 illustrates the polarization curve, and the passive potential is marked in the figure. XPS spectra measurements were performed with a LAS-3000 combined XPS/AES/SIMS surface analysis system using a Al K a radiation (hv = 1486.6
Table I Analysed
compositions
(wt%X) of the steel tested
C
Mn
Al
Si
Fe
0.90
30.2
9.22
0.06
balance
-I?001 IV
I
I
IV
10”
I IO’
I
I
IO’
IO’
I IOJ
( IO’
IO”
, Fig. 1. Polarization solution.
curve of Fe-30Mn-9Al
alloy in 1 M Na,SO,
eV). The background pressure in the sample chamber was about 2 X 10m9 Torr. The energy of the primary electron beam and the Ar+ sputtering beam are 3 and 2.5 keV, respectively. The sputtering rate was calibrated to be 2.5 i min-’ by ion etching of a Ta sample covered with Ta,O, film of known thickness. However, the sputtering depths are reported without correction for possible difference in sputtering yield between the passive film and TazO, reference oxide. The binding energies of the oxide and metallic states of Fe2p, Mn2p, A12p and 01 s were referred to the elemental carbon 1s line at 284.6 eV, recorded from graphite. The obtained XPS spectra were fitted by using a convoluted GaussianLorentzian line shape after removing the Shirley background [ 12-J.
3. Results and discussion The XPS depth-concentration profiles for the passive film formed on Fe-30Mn-9Al alloy in 1 M Na, SO, solution at 580 mV (SCE) were determined. Fig. 2 shows the XPS spectra of outermost surface for the passive film formed on Fe-30Mn-9Al alloy. The 01s peak is fitted into three components. The peak with a binding energy of 530.58 eV is at-
X.M. Zhu. Y.S. Zhang/Applied
13
Surface Science 125 (1998) 11-16
1800
50
200 0 707
702
712
717
Binding 600
722
0
727
732
631
636
641
646
656
651
661
Binding energy (eV)
energy (eV) 12000
[
r
10000
500
400
300
200
2000
100
0
69
70
71
72
73
74
75
76
77
78
n -525
79
527
529
XPS spectra for the passive
533
535
537
Binding energy (eV)
Binding energy (eV) Fig. 2. Computer-fitted sputtering.
531
film of Fe-30Mn-9Al
tributed to O’- (or M-O bonds), while the peak at 532 eV is assigned to OH- (or M-OH bonds) and the peak at 533.28 eV to H,O (bound water). From the reported work [ 131, the 01s line (about 530 eV) has been used extensively in the analysis of oxide surface species. Differences between hydroxyl oxygen (OH-) and oxide oxygen are usually recognized by an 01s shift of l- 1.5 eV. Bonding of water molecules in different surface configurations appar-
alloy formed
in
I M Na,SO,
at 580 mV (SCE), prior to
ently cause binding energy shifts about a 3 eV range. The Fe2p,,? peak at a binding energy of 724.56 eV and the Fe’tp,,, peak at a binding energy of 7 11.2 eV are due to an Fe3+ hydroxide. The Mn2p line is fitted into two components. The Mn2p,,2 peaks at a binding energy of 654.33 eV and 652.53 eV and the Mn2p,,, peaks at a binding energy of 642.37 eV and 640.96 eV are attributed to the presence of MnO, and MnO, respectively. There are two promi-
nent satellite peaks located between Mn2p,,? peak and Mn2p,,, peak. The Al,, line is split into two peaks of 75.28 eV and 74.18 eV representing A13+ hydroxide and Al’+ oxide, respectively. The transitions in binding energy and valence state of 0. Fe, Mn, and Al which obtained from XPS depth-concentration profiles are listed in Table 2. The 01s peaks at binding energy of 530.38 to 530.60 eV, 531.44 to 532.00 eV and 532.48 to 532.74 eV are corresponding to oxygen in oxides of Fe and Mn, in hydroxide and oxide of Al and in H,O, respectively. The fitted bind energy values of Fe2p,,?, and A12p in XPS spectra of the passive Mn2p,/? film correspond to the chemical valent states of Fe3+, Fe’+ and Fe”. MnJ+, Mn’+, Mn’+ and Mn” and Al”’ and Al’, which are due to the presence of
Table 2 Effect of sputtering Na,SO, solution
on the transition
of valence
Fe,O,, Fe0 and metallic Fe. MnO,, MnO, Mn,O, and metallic Mn, AI(O Al,O, and metallic Al in passive film, respectively. It is- difficult to differentiate between y-Fe,O,, a-Fe,O, (or their hydrates) or Fe,O, on the basis of XPS. The sputter-depth profiling showed that0 iron hydroxide disappear after sputtering for 10 A. The Fe’+ hydroxide was likely transformed into Fe3+ oxide. If Fe”+ hydroxide is reduced to Fe3+ oxide by preferential sputtering of oxygen, the presentation of Fe3+ oxide after the first sputtering may be a false artifact. However, two facts show that there is probably really a rej+ oxide in the layer of film after sputtering 10 A: (1) The affect of chemical alteration by ion bombardment, if existing, was a systematic disturbance which will not only disturbs the layer of sputtering 10 i and Fe”+
state of Fe?p. Mn2p. Al2p and 01s peaks for Fe-30Mn-9Al
Mn
Al
alloy passivated
in
0
Sputtering
Fe
depth(A)
Intensity (counts)
2p,),?
vs
Intemity kounts)
2p3,?
VS
Intemity (county)
7-p
VS
Intenhity (counts)
lb
vs
0
1737
711.20
Fe’+-hy
225 721
642.37 630.96
Mn’+-ox MI?+-ox
340 322
75.28 74.18
Al’+-hy Al’+-ox
IO
5047
710.35
Fe’+-ox
Al”-hy Al’+-ox
710.31
Fe”-ox
525 655
75.05 74.1
Al’+-hy Al’+-ox
35
5689
710.18
Fe’+-ox
159 663
74.88 73.98
Al’+-hy Al’+-ox
45
6395
710.33
Fe3’-ox
389 668
75.08 74.28
Al’+-hy Al’+-ox
75
5821 3533
710.16 707.42
Fe’+-ox Fe”
61 I 389
71.88 74.01
Al’+-hy Al’+-ox
175
5655 7490
709.86 707.12
Fe?+-ox Fe”
Mn’+-ox Mn’+-ox Mn” Mn’+-ox Mn’+-ox Mu” Mn”-ox Mn’+-ox Mn” Mn’+-ox Mn’+-ox Mn” Mn’+-ox MI?+-ox Mn” Mn’+-ox Mn”
74.88 73.98
6102
642.54 640.78 638.26 642.65 641.10 638.69 642.30 640.77 637.94 632.59 641.13 638.03 642.69 640.99 639. I I 631.67 638.97
594 653
20
496 509 51 127 625 I61 767 525 I02 618 913 73 1008 IO68 417 2161 890
127 191
74.88 74.01
Al’+-hy Al’ +-OX
I75
5626 13542
709.41 707.01
Fe’+-ox Fe”
2120 232 I
641.48 638.83
Mn’+-ox Mn”
620 40
74.50 72.23
Al’+-ox Al”
237
30 500
707.03
Fe’
8750
638.93
Mu”
427 136
74.40 72.28
Al’+-ox Al”
5592 8962 3722 3520 8372 8606 3016 7944 8604 2365 81 19 8300 2871 1654 8319 1538 6298 7159 3379 6203 6535 1464 4414 4715 1056 3195 2833
533.28 532.00 530.58 ___. 5-i? 74 53 I .58 530.43 532.58 53 I .53 530.18 532.67 531.52 530.43 532.58 531.58 530.60 532.53 53 I .5-I 530.58 532.48 53 I .44 530.37 532.53 53 I .48 530.47 532.63 53 I .45 530.38
H,O M-OH M-O H,O M-OH M-O H-0 M-OH M-O H,O M-OH M-O Hz0 M-OH M-O H,O M-OH M-0 H10 M-OH M-O Hz0 M-OH M-O H,O M-OH M-O
VS = valence state: ox = oxide: hy = hydrate.
I M
X.M. Zhu, Y.S. Zhang /Applied Surface Science 125 ( 1998) I I-16
hydroxide but also the others layers and A13+ hydroxide as well as Mn3+ oxide after the first sputtering. From the Table 2, the intensity of Mn”+ oxide and A13+ hydroxide increased about twice after the first sputtering, and this means that the reduction of ion bombardment on Mn’+ oxide and A13+ hydroxide is small or tolerable. (2) On the basis of most studies on passive film, in general, the thinner Fe’+ hydroxide is present on the outer surface of the passive film while the Fe3+ oxide is located in the inner part. With increased sputtering depth, the intensity of oxygen peak in H,O decreases, the and A12p peaks shift toward low Fe2p,,zY Mn2p,,, bind energy and the valent states show a transition from Fe3+ to Fe’+ and to Fe’, from Mn’+ to Mn3+ to Mn’+ and to Mn” and from A13+-hydroxide to A13+-oxide and to Al0 while the contributions from underlying Fe’, MnO and Al0 increase. From the XPS depth profile analysis, it is likely that the passive film of Fe-30Mn-9Al alloy is much thicker than that of conventional stainless steels, and there seems to be a transition layer consisted of low valent oxides and the metallic elements between the passive film and the alloy matrix. It should be noted that the valence states of oxides are not easy to determine exactly by XPS owing to the superposition of the Fe’+ (709.3-710.7 eV) and Fe3+ (710.3-711.5 eV) peaks, the Mn’+ (640.4-641.5 eV1, Mn”+ (641.2641.7 eV> and Mn” (641.6-642.8 eVI peaks as well as the presence of satellite peaks. As show in Fig. 2 and Table 2, the passive film formed on Fe-30Mn-9Al alloy in Na,SO, solution contains H,O which is prevalent at the outer surface but which is also contained in bulk of the film. This information is consistent with the results of previous investigation which have used XPS and SIMS data to show that water is present in the passive film on iron [14]. There is disagreement, however. as to whether bound water is contained in the outermost surface alone [15] or in the bulk of the passive film as well [ 161. The present results of XPS analysis tend to support the models based on the existence of bound water in the passive film. The results shown in Fig. 2 and Table 2 suggest that the passive film consisted of bound water, hydroxyl species, hydroxide of AI and Fe and oxides of Fe, Mn and Al. It is noteworthy that the presence of bound water and the hydroxyl species existing 237 A into the passive film
15
may play an important role in improving its passivity, mainly by inducing formation of an amorphous film structure [ 141. The electrochemical corrosion resistance is probably imparted by a barrier film of bound water, hydroxides and oxides of Fe and Al, while the Mn oxides in passive film reduce the resistance to electrochemical corrosion because of its fragile and instable structure. The adverse effect of Mn in Fe-Mn-Al alloys was also recognized by noting an increase in corrosion current density and a decrease in corrosion potential in 1 M Na,SO, solution [17]. Manganese is one of the most important austenite-stabilizing elements in alloys, which not only affects the structure of alloys, but also influences the surface properties such as the formation of passive film under the electrochemical polarization. The development of Fe-Mn-Al alloys involves a compromise between economical consideration and corrosion resistance, because the manganese tends to degrade passivity of the alloys.
4. Conclusions XPS studies on the passive film formed on Fe30Mn-9Al alloy in 1 M Na:SO, solution indicate that: ( 1) The broad envelops of 01 s consist of bound water, M-OH and M-O bonds contributions. (2) Iron is present in the passive film as Fe3+ hydroxide, oxides of Fe3+ and Fe’+ and metallic Fe, manganese as oxides of MnJ’ and Mn’+ and metallic Mn and aluminum as Al’+ hydroxide, A13+ oxide and metallic Al. (3) Bound water is present in the passive film. (4) It is difficult to substitute the Fe-Mn-Al alloys for the conventional stainless steel due mainly to the presence of instable manganes oxides in the passive film of Fe-Mn-Al alloy.
Acknowledgements This project has been supported by the National Natural Science Foundation of China under Grant 59471027 and the State Key Laboratory for Corrosion and Protection of Metals. We would like to thank Profs. Cao Chunan, Lin Haichao and Wang
16
X.M. Zlzu. Y.S. Zhang / Applied Surjace Science 125 ( 1998) I I - 16
Wenhao, Mrs. Sun Yuzhen and Mr. Gong Yandong for their technical support.
References [I] S.K.
Banerji. Met. Prog. 113 (1978) 59. [2] J.C. Garcia, N. Rosas, R.T. Rioja, Met. Prog. 122 (1982) 47. [3] R. Wang, F.H. Beck, Met. Prog. 123 (1983) 72. [4] R. Wang, R.A. Rapp, in: Proc. 9th Int. Corrosion Cong.. Toronto, Canada. June 1984, Vol. 4, p. 545. [5] M. RuSEBk, T.P. Pemg, Corrosion 52 (1996) 464. [6] S.C. Chang, J.Y. Liu, H.K. Juang, Corrosion 51 (1995) 399. [7] M. Cavallini. F. Felli. R. Fratesi. F. Veniali, Werkst. Korros. 33 (1982) 281.
[S] C.J.
[9] [IO] [ll] [I21 [ 131 [14] [15] [16] [17]
Altstetter. A.P. Bentley. J.W. Fourk, A.N. Kirkbrid. Mater. Sci. Eng. 82 (1986) 13. S.C. Tjong. Surf’. Coat. Technol. 28 (1986) 181. T. Wen, B. Jing, T. Ju. J. Mater. Sci. 22 (1987) 3517. S.T. Shin, C.Y. Tai, T.P. Perng, Corrosion 49 (1993) 130. Y. Gong, Acta Met. Sinica 32 (1996) 219. D. Briggs. M.P. Seah, in: Practical Surface Analysis, 2nd ed., Wiley. New York. 1990. T.E. Pou. O.J. Murphy, V. Young, J.OM. Bockris. L.L. Tongson, Electrochem. Sot. 131 (1984) 1243. S.C. Tjong, E. Yeager. J. Electrochem. Sot. 128 (1981) 2251. O.J. Murphy, J.O’M. Bockris, T.E. Pou. D.L. Cocke, G. Sparrow. J. Electrochem. Sot. 129 (1982) 2149. X.M. Zhu. Corros. Sci. Protect. Technol. 8 (1996) 36.