Raman identification of corrosion products on automotive galvanized steel sheets

Abstract

Iron oxides (haematite, maghemite, magnetite), (oxy)hydroxides (lepidocrocite), carbonates, as well as zinc carbonate and oxide, have been identified on corroded galvanized steel samples after corrosion accelerating tests in the laboratory and compared with those observed on samples taken from vehicles that have been in circulation for five years in severe weather conditions. Spectra recorded on the corroded parts are compared with synthesized compounds. (Hydroxy)carbonates are clearly evidenced on galvanized and phosphated steel sheets. Corrosion layers beneath the paint could be detected. White regions always correspond to a ZnO-rich phase but maghemite (g-Fe 2 O 3 ) and sometimes akaganite (b-FeOOHCl) are observed at the centre (maroon) of very corroded spots. Maghemite is observed in strongly corroded regions. Goethite (a-) and lepidocrocite (g-FeOOH) (and akaganite) are observed at the surface of less corroded regions of phosphate-free galvanized steel and are absent for phosphate-coated steel. Green rust is observed only on galvanized samples corroded in the laboratory.

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

“…Consequently, the 880 and 981 cm −1 bands correspond to the respective bridging V-O-V and terminal V=O structures in distorted octahedrally coordinated VO 6 species, even in the TiO 2 -supported binary and ternary component systems employed here, and indicate the presence of polymerized mono-oxo vanadate species [49,53,55,56,58]. All the iron oxides discussed in the XRD measurements, except for magnetite, exhibit Raman bands at 1000-1600 cm −1 in which no Raman signals by TiO 2 appear [30,49,51,59]. However, all the 2.73% Fe 2 O 3 -promoted catalysts gave no bands in the frequency region as well as at 800-1100 cm −1 (Figure 8b,d).…”

A methodology for Raman characterisation of MoDTC tribofilms and its application in investigating the influence of surface chemistry on friction performance of MoDTC lubricants

“…and A 1g peaks. These additional peaks were assigned to the formation of iron oxide [41]. The analysed region was observed to have developed dark spots after analysis with 10 mW laser power as seen in the inset image in Figure 2 (a).…”

Potential and Drawbacks of Raman (Micro)spectrometry for the Understanding of Iron and Steel Corrosion

“…2. Raman signature of the main (crystalline) iron oxi(hydroxy)des observed in corrosion films (after Colomban et al, 2008).…”

“…Note that Raman analysis is possible through a layer, inorganic (enamel, ceramic matrix (Wu et al, (1997); Gouadec et al(1998)) or organic one (paint, e.g. Colomban et al, 2008). Typically, good Raman signatures are obtained up to 20 to 40 µm below the surface.…”

“…Although the reference signatures of pure iron oxides are well established, those of the mixed compounds like spinels associating Fe, Mn, Cr, Ni,… atoms or of oxyhydroxycarbonates, hydrated or not, are very poorly documented (Colomban et al, 1999;Colomban et al 2008;Cvejic et al, 2006). These phases may be unstable under the laser spot and may transform into more stable ones having different structure.…”