High Resolution In Situ XANES Investigation of the Nature of the Passive Film on Iron in a pH 8.4 Borate Buffer

Abstract

The nature of the passive film grown on iron in a pH 8.4 borate buffer at a high potential [+0.4 V (MSE)] was investigated with high resolution in situ XANES (x-ray absorption near-edge spectroscopy). The pre-edge peak at the base of the Fe K edge showed no evidence of the splitting associated with structures such as c~-Fe2Q, a-FeOOH, and ~]-FeOOH which contain iron that is entirely octahedrally coordinated to oxygen. The single pre-edge peak is consistent with the proposed ~]-Fe2OJFe304 structure (in which one-third of the iron ions are tetrahedrally coordinated) or with a disordered structure with distorted coordination polyhedra.

On the onset of current oscillations at the limiting current region emerged during iron electrodissolution in sulfuric acid solutions

“…Tafel slopes and reaction orders with respect to H + and solution anions for the active region were determined and several dissolution mechanisms were proposed [32]. The composition and structure of the oxide film in the passive region were also investigated thoroughly in both, early and recent studies, although oxide composition is still disputed [33][34][35]. Substantial experimental evidence points to the fact that H 2 O involves in both dissolution and passivation reactions.…”

Electrochemical Behaviour of Iron in NaOH 0.01 mol/L Solutions Containing Variable Amounts of Silicate

“…Many investigations were carried out using highly alkaline solutions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] or using buffer solutions as carbonate/bicarbonate [19][20][21][22][23][24][25][26] or borate buffer [27][28][29][30][31][32] when a constant and not very high pH is desirable. Many products have been identified as resulting from the anodic polarization of iron at different potentials, by different surface analysis techniques [6][7][8][9][10][11][12][13]22,26,[33][34][35][36][37][38][39][40]…”

“…Several electrochemical techniques have also been used to investigate the kinetics of the formation of these products and among them cyclic voltammetry is one of the most used [2][3][4][5][6][7][8][14][15][16][17][18][19][20][21][22] . The surface analysis techniques that perform in-situ analysis have the great advantage of avoiding decomposition and/or dehydration of products formed which is inevitable with ex-situ analysis due to the high vacuum conditions and to the heating promoted by electron bombardment 1,14,28,[33][34][35][36][37][38] .…”

“…In-situ UV and visible spectroscopy techniques have also determined such a bi-layer structure 15 . Another proposition for the film passive composition based in elipsometric results 7 , XANES in-situ 27,28 and other optical techniques 37,39,44 The in-situ analysis results show that the film presents an amorphous character due to water presence which is an Article essential factor for passivation and this amorphous character is destroyed if the film is dried 10,14,34,35 . When a passive film is described as a double layer film, the inner layer is considered a barrier layer and the outer layer is a substrate for Fe(II)/Fe(III) redox reactions during potential cycling 6,7,22,42,43 .…”

GDOES depth profiling analysis of the air-formed oxide film on a sputter-deposited Type 304 stainless steel

“…Films of this kind, formed on ferrous metals, play a key role in corrosion protection. Thus, the compositions and structures of the films have been studied extensively both ex situ and in situ, for example, using XPS 4 and x-ray adsorption nearedge spectroscopy (XANES), 5,6 respectively. However, depth profiling analysis of thin oxide films on ferrous metals by various surface analytical techniques has not been achieved with sufficient resolution and reproducibility for precise understanding of the mechanisms of film growth.…”