Depth profiling corrosion

XPS is very useful for the study of surface layers and corrosion films. In the case of corrosion films and oxides it is important to do depth profiling by coupling XPS with ion milling of the surface. Another important aspect of XPS is that the incident X-rays cause negligible damage to the surface. 

Dynamic SIMS is used for depth profile analysis of mainly inorganic samples. The objective is to measure the distribution of a certain compound as a function of depth. At best the resolution in this direction is < 1 nm, that is, considerably better than the lateral resolution. Depth profiling of semiconductors is used, for example, to monitor trace level elements or to measure the sharpness of the interface between two layers of different composition. For glass it is of interest to investigate slow processes such as corrosion, and small particle analyses include environmental samples contaminated by radioisotopes and isotope characterization in extraterrestrial dust. 

The depth profiling studies suggest that two different processes govern the formation of automotive exhaust particles. The elemental surface predominance on large particles is attributed to the deposition of volatile Pb and S species (e.g. PbBrCl, SO2) onto the surfaces of refractory iron-containing particles in the automotive exhaust system (11,12). The iron-rich particles are probably derived from corrosion and ablation of the exhaust system. The smaller, more homogeneous particles may form by a nucleation process in which PbBrCl forms rather pure molten droplets when the exhaust system temperature falls below the saturation point (12). 

The superior corrosion performance and strong adhesion of the plasma coating system can be attributed to the coating properties and, more importantly, to the nature of interfacial chemistry. Two techniques were applied to study the surface and interfacial chemistry of the plasma coating system (1) in situ plasma deposition and XPS analysis and (2) in-depth profiling of sputtered neutral mass spectroscopy (SNMS). 

XPS analysis of the corrosion film on Cor-Ten A, Table VI, gives results similar to those obtained by corrosion film mass balance, TGA, and XRD. The principal film constituents in the outer 10 nm of the film are 202 and FeOOH, with there being somewhat more iron present as Fc203 than FeOOH. This would be expected in a film that dehydrates. However, if this is true, then the 2 1 atomic ratio of oxygen to iron indicates that even the outermost surface of the film contains substantial water. ISS depth profiles for the... 

Figure 7 Corrosion depth of a group of lance and spearheads excavated in 1994. (a) Plan view, where solid lines indicate modem excavations and dashed lines show excavations during the 19th century, (b) Vertical profile (seen from SE) where dashed line indicates interface between peat and gyttja. Solid line at each point represent a projection of the lance or spear head to the vertical view plane, so long steep lines indicate artefacts deposited in a steep angle. Numbers to the left are metres above sea level...

Studies of passivation layers and corrosion phenomena, particularly with iron and magnesium using EXAFS, NEXAFS and related X-ray absorption spectroscopies have been reviewed elsewhere [589]. Using GIXAFS, depth profiling has become possible and spatially resolved studies of silver dissolution and lithium intercalation have been reported. 

Chlorides in concrete structures can be present as cast-in chlorides (in cases where chloridemixing water was used) or can be transported into concrete from the environment (seawater, de-icing salts). To distinguish between these two cases and to be able to get information on the future service life of a structure, a chloride depth profile should be determined. This is essential because the actual chloride level at the reinforcement determines the present probability of corrosion, but the profile determines the future development of corrosion. 

RBS and ERD are especially useful when, not only the composition of the samples, but also their depth profiles are to be determined in the first few pm, and the measurements should be performed fast, e.g., in a few minutes. Typical things to study are diffusion, corrosion, soKd-phase chemical reactions, and investigation of multilayers. 

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