Atomic images of 304SS surface after electrochemical treatments

Nanjo, Hiroshi; Newman, R.C.; Sanada, Norio

doi:10.1016/s0169-4332(97)00300-0

Cited by 36 publications

(34 citation statements)

References 9 publications

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“…These results are consistent with several recent investigations which have shown that passive oxide films on pure Fe [12], pure Cr [13], Fe-Cr alloys [10] and 304 stainless steel [3] are generally nanocrystalline. As such, these results provide further evidence disproving the widely-held belief that passive films must be amorphous [14].…”

Section: Discussionsupporting

confidence: 93%

“…It has been shown by others that the chemical composition of passive films on Fe-Cr alloys can be varied significantly by performing passivation at different applied potentials [2], and we have previously demonstrated that stainless steel and pure iron can be atomically flattened by electrochemical passivation treatment [3,4]. In this paper, we present preliminary results concerning the passivation of Ni-Cr alloys.…”

Section: Introductionmentioning

confidence: 80%

“…Since the predictions of percolation theory depend on the lattice structure, different compositional thresholds are predicted for fcc alloys, such as Ni-Cr. Specifically, for a bcc lattice, P c [1][2][3] is $10 at.% and P c [1,2] is $18 at.%, whilst the corresponding values for an fcc lattice are $6 and $12 at.% respectively. Therefore, in this work we aimed to test the percolation-based model of passivity using thin film Ni-Cr alloys and performing experiments that were similar to those carried out by other researchers using thin film Fe-Cr alloys.…”

Section: Resultsmentioning

confidence: 99%

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Atomic-scale flattening of Ni–Cr alloy surfaces by electrochemical passivation treatments

Nanjo¹,

Laycock²,

Deng³

et al. 2004

Current Applied Physics

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 99%

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Atomic-scale flattening of Ni–Cr alloy surfaces by electrochemical passivation treatments

Nanjo¹,

Laycock²,

Deng³

et al. 2004

Current Applied Physics

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“…The oxide was found to consist of circular protrusions. Nanjo et al 14 imaged the surface of 304 stainless steel in air after passivation in 0.1 M H 2 SO 4 . As with the binary alloys it was observed that the extent of crystallinity of the oxide phase increased with time from passivation.…”

mentioning

confidence: 99%

An STM Study of the Nanocrystalline Structure of the Passive Film on Iron

Rees

Ryan

McPhail

2002

Electrochem. Solid-State Lett.

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Scanning tunneling microscopy ͑STM͒ has been used to demonstrate the nanocrystalline nature of the passive film on pure Fe formed at high anodic potential in near neutral borate buffer solution. The average lateral grain size was of the order of 5 nm. This confirms suggestions based on previous surface X-ray diffraction data. The oxide grains are clearly visible superimposed on the substrate metallic grains and form as a result of a rapid nucleation and growth process during electrochemical passivation.Since the 19th century, when Faraday first described the passive nature of Fe 1 there have been numerous theories proposed to account for the observed behavior. The formation of an ultrathin passive oxide film ͑ϳ3-4 nm thick͒ on the metal surface poses a kinetic barrier to dissolution affording protection to the underlying metal. Due to its obvious technological importance, the structure and chemistry of the passive film on Fe has been the subject of much work. However, despite the wide range of analysis techniques used, the structure of the oxide film has remained disputed until recently ͑see Ref. 2, 3, and references therein͒. The crystallinity of the passive film was confirmed by scanning tunneling microscopy ͑STM͒ 4 and subsequent crystallographic analysis based on in situ synchrotron X-ray diffraction ͑XRD͒ 2,3 data finally provided a detailed atomic picture of the passive film. This work showed that the passive film is a highly defective spinel type oxide that is not identical to any of the bulk oxides of iron. Furthermore, from the peak broadening in the XRD data the authors suggested that the film is nanocrystalline with a grain size on the order of 5-8 nm in plane and 2.5-3.5 nm out of plane. Such a suggestion had been made decades earlier by Cohen and co-workers based on electron diffraction measurements of the air-formed oxide 5 but had been mostly overlooked as workers concentrated on amorphous vs. crystalline models of the passive state. In this early work they estimated that the oxide film consisted of microcrystals of Ͻ3 nm lateral dimension. 5 In this paper, we present STM data that directly confirm the nanocrystalline nature of the passive oxide.STM is unique in that the structural determination is direct and inherently local. It has been used for both in situ and ex situ examination of passive films on a range of metals and alloys including Fe, Ni, FeCr, stainless steels, and Cr. The passivation of iron in borate buffer has been the subject of many investigations using a wide range of techniques. The first STM study to image the passivation process of polycrystalline iron in borate buffer, pH 8.4, was conducted by Bhardwaj et al. 6 Passivation was observed to begin by the initial formation of oxide clusters which proceeded to fuse together to form the oxide layer. More recently, Diéz-Pérez et al. 7 used in situ electrochemical STM ͑ECSTM͒ to image the first stages of the electrochemical growth of the passive film on iron in borate buffer at pH 7.5. However, the solution pH chosen for this work mea...

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“…Passivation was a historically used fundamental method to make atomically flat surface [31]. In order to study the difference between the air-formed oxide film and the oxide film formed during electrochemical passivation, we prepared two different samples at different conditions.…”

Section: Passivation Treatment (Pa)mentioning

confidence: 99%