Iron Auger spectroscopy

Reactions involving mackinawite and an oxidized sulfur species have been repeatedly shown to lead to pyrite formation (e.g., Bemer, 1969 Rickard, 1969, 1975). In addition, Wilkin and Bames (1996) and Penning et al. (2000) have shown that pyrite formation is exceptionally rapid when the mackinawite is pre-oxidized (e.g., exposed briefly to air) prior to the experiment. Based partly on X-ray photoelectron and Auger spectroscopy results of pyrrhotite oxidation (Mycroft et al., 1995), Wilkin and Bames (1996) hypothesized that this oxidative exposure initiates an iron-loss pathway similar to Equation (13). In sulfidic solutions, Fe(II) oxyhydroxides, shown as a product in this reaction, would not accumulate, but instead would undergo reductive dissolution by a reaction similar to Equation (14) ... 

Figure 11-1. Adsorptive interaction of sulfur compounds with iron surfaces. Detection of sulfur retained adsorptively on iron surfaces by Auger spectroscopy. The sliding friction experiments were run at 0.5 cm/s, 0.981 N, 295 K. (a) Hydrogen sulfide. (b) Methyl mercaptan. From data by D. H. Buckley [8].

Auger spectroscopy was used by Buckley to study the interaction of the following chlorine compounds with sputter-cleaned iron surfaces methyl chloride, ethyl chloride, vinyl chloride and benzyl chloride [7, 13]. With the exception of benzyl chloride, these halogen compounds left... 

Molecular orbital/energy band calculations have been performed for a range of iron(II) sulfides and there is interest in the band-like valence-electron states in FeSj and also in their bulk and surface properties typified by studies using Auger spectroscopy " and X-ray absorption. The extensive work in this area published during the period 1960-1969 is contained in an excellent review by Ward. Unfortunately, discussion about the fascinating tricyclic iron(III) polysulfide anion [Fc2S 2] and its reactions with, for example, activated alkynes " are outside of the scope of this section. 

The migration of K to the surface of the reduced catalyst [40] has been demonstrated by energy dispersive X-ray analysis [28], by field iron mass spectroscopy [222, 223], by chemisorption of CO, CO2, N2and H2 [207, 220] by scanning Auger electron spectroscopy [209-211], and by high-voltage electron microscopy [224]. 

Other spectroscopic techniques used to characterize iron oxides are photoelectron (PS), X-ray absorption (XAS), nuclear magnetic resonance (NMR) (Broz et ah, 1987), Auger (AES) (Seo et ah, 1975 Kamrath et ah, 1990 Seioghe et ah 1999), electron loss (EELS)), secondary ion mass (SIMS) and electron spin resonance (ESR) spectroscopy (Gehring et ah, 1990, Gehring Hofmeister, 1994) (see Tab. 7.8). Most of these tech-... 

Quantitative Auger electron spectroscopy depth profiling of iron oxides formed on Fe (100) and polycrystalline Fe by exposure to gas phase oxygen and borate buffer solution. Langmuir 6 1683-1690... 

X-ray Photoelectron Spectroscopy (XPS) tests were conducted on surfaces lubricated with a sulfur-containing extreme pressure additive, dibenzyl sulfide (Baldwin, 1976 Bird and Galvin, 1976). The films can arise from the use of additives that contain sulfur, phosphorus, chlorine, bromine, or boron and the differences in reactivity are affected by the formation of protective layers. Triboinduced electrons are said to activate the formation of iron halides, iron phosphates and iron sulfides (Dorison and Ludema, 1985 Grunberg, 1966 Kajdas, 2001 McFadden et al., 1998 ). When a chemical reaction takes place, e.g., oxygen interacts with aluminum to form aluminum oxide, a large oxygen peak is seen at approximately 500 eV in the Auger electron spectra (Benndorf et al., 1977 Nakayama et al., 1995). 

Some of the most recognized tests to detect, measure, and quantitate the chrome/iron ratio and to ensure that a passive layer has been established are the Ferroxyl Test for Free Iron, X-Ray Photoelectron Spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis (ESCA), and Auger Electron Spectroscopy (AES). 

Goodman, Kelley, Madey, and Yates (44, 45) used Auger electron spectroscopy (AES) to monitor ad-layer development on nickel Dwyer and Somorjai studied iron and rhodium (35, 46) and Bonzel et al. (36. 47) used both AES and XPS in a study of iron. The findings of the various studies are to a large extent corroborative, and we discuss in detail the work of Bonzel ef al. to illustrate the findings typical for these studies. 

The above ideas that anion-cation pair sites are the surface sites for CO and CO2 adsorption on magnetite was verified directly by Udovic and Dumesic (43 ). These authors prepared films of magnetite on polycrystalline iron foils and varied the oxidation state of the surface by vacuum-annealing at different temperatures. In short, it was shown by Auger electron spectroscopy and X-ray photo-... 

The macro-scale investigations showed that pretreatment of an iron surface with steam at 700°C itduces a dramatic increase in the catalytic activity for carbon deposition from hydrocarbons. Spectroscopic analysis (Auger and Mossbauer) combined with weight increase measurements prove that treatment of iron with steam at 700°C results in the conversion of the surface of the iron to FeO. At 800°C, this process is not just limited to the uppermost surface layers but penetrates to an appreciable depth of the material after a three hour treatment. Indeed Mossbauer spectroscopy data shows that nearly all of a 0.013 cm Fe foil is transformed to FeO in this time at 800°C. It should be mentioned that the reaction of steam with iron to produce FeO may be possible at temperatures above 570°C (3). The nonstoichiometric nature of FeO has been the subject of "a considerable number of papers. It is known, however, that the defects present in this material are vacant cation sites and trapped positive holes (26). 

Hochella MF Jr (1988) Auger electron and X-ray photoelectron spectroscopies. Rev Mineral 18 573-638 Hofer HE, Brey GP, Schulz-Dobrick B, Oberhansi R (1994) The determination of the oxidation state of iron by electron microprobe. Eur J Mineral 6 407-418... 

X 10 torr seconds. Auger electron spectroscopy and 16) has shown that a layer which can be represented as Fe O OH protects iron from further attack. Direct evidence of hydrogen being present in the passive film formed in solution was provided by mass spectrometry (30). Electron diffraction (2, 29) has shown tHat the protective surface layers wHTch form on iron which has been air oxidized or passivated in solution are surprisingly similar. The structures are based on the cubic close packed oxygen lattice of y Fe O OH, or Fe304 ... 

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