Oxide films, EXAFS studies

Chromium. So-called stainless steels contain in their alloys elements soeh as Cr, Ni, Co, and Mo) that eventually become incorporated into the passive oxide films. Cr(III), as shown by EXAFS studies with hydrous ferric acxie and goethite (18), forms inner-sphere surface complexes in the form of... 

The use of surface EXAFS in the study of passive films represents a natural application of the technique, and in fact, the studies by Kruger and co-workers on the passive film on iron represent the first reported. In their first studies, they employed vacuum-deposited iron films on glass slides and subsequently oxidized the films in either nitrite or chromate solution. They obtained the EXAFS spectra for the oxidized films, employing a photocathode ionization chamber (detecting the emitted electron current) and compared these with spectra for y-FeO(OH), y-Fe203, and Fc304. Although these studies were not in-situ, they did not require evacuation of... 

The solid wear particles from ZDDP films produced in lubricated contacts contain phosphorus, sulfur and zinc from the ZDDP molecule and oxygen mainly from the surrounding air environment. They also have a low iron content. Ex situ examination by XAS, EELS and CEMS of these particles (configuration shown in Fig. 5a) has been carried out to provide local analysis of the iron atoms, since their localized environment in the surface film is of great interest it is related directly to the wear of the steel surface and can also play a key role in the adhesion mechanisms of the film. In order to investigate this aspect, a study was made by XAS (EXAFS plus XANES) of a collection of wear debris from two lubricated tests, with and without ZDDP in the lubricant base, respectively. The processed EXAFS data presented in Fig. 8 show the RDFs of iron atoms (noncorrected phase shifts) in four samples data from the standards, pure crystalline iron and iron oxide have been included for comparison. From this EXAFS study, some important results can be deduced [4] ... 

Detailed studies were conducted by infrared, TPD, XPS but also by more sophisticated techniques such as CP-MAS solid state NMR or EXAFS, on the various steps by which molybdenum can be deposited on alumina supports starting from [Mo(CO)e]. Indeed, thin films of molybdenum or of its oxides have wide application as gas sensors or solar cell catalysts. 

Most recently, they have developed a cell configuration for the study of modified electrodes that employs, as a working electrode, colloidal graphite deposited onto kapton tape (typical window material). Such an arrangement minimizes attenuation due to the electrolyte solution. They coated the working electrode with a thin film of Nafion (a perfluoro sulfonate ionomer from E. I. DuPont de Nemours, Inc.) and incorporated [Cu(2,9-dimethy-1,10-phenanthroline)2] by ion exchange. They were able to obtain the EXAFS spectra around the copper K edge for the complex in both the Cu(I) and Cu(II) oxidation states. 

---