Oxide film, iron

The lifetime of a conventional exhaust system on an average family car is only 2 years or so. This is hardly surprising - mild steel is the usual material and, as we have shown, it is not noted for its corrosion resistance. The interior of the system is not painted and begins to corrode immediately in the damp exhaust gases from the engine. The single coat of cheap cosmetic paint soon falls off the outside and rusting starts there, too, aided by the chloride ions from road salt, which help break down the iron oxide film. 

Under the hot deaerated (reducing) conditions normally found on the surfaces of pre-boiler FW heaters, FW lines, and boiler surfaces, a dense, passive, black, iron oxide film of magnetite (Fe304) naturally forms. 

Brezesinski, T. Groenewolt, M. Antonietti, M. Smarsly, B. 2006. Crystal-to-crystal phase transition in self-assembled mesoporous iron oxide films. Angew. Chem. Int. Ed. 45 781-784. 

Iron films behave in every way similar to nickel films except that upon admitting oxygen, about seven oxygen atoms are sorbed instantaneously for every crystallographic site, forming an iron oxide film seven atom layers deep, and except that the heat of adsorption of hydrogen on such an oxide covered film is almost identical with that on the clean iron surface even immediately after the oxidation has taken place. 

Schwertmann, U. Friedl, J. (1998) Thin iron oxide films on pebbles in ferriferrous streams. N. Jb. Miner. Mb. 2 63-67... 

Yubero, F. Gonzalez-Elipe, A.R. Tougaard, S. (2000) Determination of growth mechanisms by x-ray photoemission and ion scattering spectroscopies Application to thin iron oxide films deposited on Si02. Surface Sci. 457 24-36... 

Iron-only hydrogenase, dithiolate-bridged compounds as biomimetic models, 6, 239 Iron oxide films, synthesis, 12, 51 Iron-palladium nanoparticles, preparation, 12, 74 Iron-platinum bimetallic clusters, with isocyanide clustes,... 

Figure 4.4.7 (A) CO2 production over Pt(lll), iron oxide films on Pt(lll), and Pt/ Fe3C>4(lll) annealed to 600 and 850 K. (B) STM images of the encapsulated Pt particle on Fe3C>4(lll) and, for comparison, of the FeO(lll)/Pt(lll) film, both exposed to 20 mbar O2 at 450 K. The scheme illustrates the reaction mechanism. (See the text.)...

Sun YN, Qin ZH, Lewandowski M, et al. Monolayer iron oxide film on platinum promotes low temperature CO oxidation. J Catal. 2009 266 359-68. 

The Kelvin probe was used to study the oxidation state at the interface to the metal surface. Grundmeier and Stratmann have shown that the potential measured by the SKP depends on the oxidation state of iron oxide films according to the following equation [9] ... 

FIGURE 10.8. Ferric hydroxide formation at a crack in an iron oxide film on an iron surface... 

Other recent preliminary studies have demonstrated the utility of X-ray microprobes to interrogate the distribution and chemical speciation of transition metals and other elements in single cells of Pseudomonas fluorescens adhered to Kapton film and the DMRB, Shewanella putrefaciens adhered to an iron oxide film (Kemner et al. 2001). While preliminary, this study demonstrates the utility of synchrotron X-ray microprobes to examine single fully hydrated bacterial cells. The Ca K map of P. fluorecens adhered to Kapton film can be used to define the location of the bacterium cell on the Kapton. The Cr Ka map of the same bacterium exposed to a Cr(VI) solution demonstrates a different distribution than the Ca, indicating that the Cr is not concentrated within the cell (Fig. 13). 

Iron oxide films and nanoparticles are currently being extensively investigated due to their applications in catalysis, magnetic recording media, gas sensors, and anticorrosion protective paints. The production of magnetic... 

For Curve B the solution was sodium chloride-boric acid buffered to pH 7.8. The polarization conditions were the same. However in the presence of the chloride the maximum current before the onset of passivity was increased and the potential range for passivity was decreased. The high currents observed in the "passive region" were mainly due to localized attack which leads to pitting. The major part of the surface is still covered by the same type of iron oxide film as that found with the pure borate buffer. 

Interestingly, iron oxide films prepared by spray pyrolysis of iron nitrate solutions containing 0.05 M titanium tetrachloride were reported to have a band gap of 1.27 eV, which would presumably be too low for solar hydrogen production for the reasons stated above. Indeed, the films prepared with this level of titanium displayed the poorest photocurrents under illumination from 150 mW cm of a Xe arc lamp. Kumari et al. [61] noticed that as the concentration of titanium present in the precursor solution increased, the flat band potential and the photocurrent onset moved to a more cathodic potential. This is in general agreement with Glasscock et al. [68]. 

Fig. 8 Scanning electron micrographs of iron oxide films prepared from (a) spray pyrolysis of Fe (acetylacetonate)3 solutions, undoped (reproduced with permission from [60]), (b) spray pyrolysis of iron(III) chloride solutions doped with 5 at.% Ti (reproduced with permission from [59]), (c) spray pyrolysis of iron(III) nitrate solutions undoped left) and doped with Ti eight) at a magnification of 200,000 (reproduced with permission from [61], and (d) magnetron sputtering (reproduced with permission from [68])...

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