J. R. Gancedo

Characterisation by X-ray photoelectron spectroscopy of thin MnxCo3−xO4(1≥x≥0) spinel films prepared by low-temperature spray pyrolysis

Abstract Thin films of MnxCo3−xO4 with x=0; 0.25; 0.5; 0.75; 1, prepared by low temperature (150°C) spray pyrolysis onto a glass substrate with a sublayer of doped SnO2 were examined by X-ray photoelectron spectroscopy. The binding energies of the photoelectron peaks observed for the transition metal ions and the oxygenated ions were recorded. The results indicate that in these materials cobalt is present in both divalent and trivalent states, whereas manganese is found to be Mn3+.

Corrosion resistance of single TiN layers, Ti/TiN bilayers and Ti/TiN/Ti/TiN multilayers on iron under a salt fog spray (phohesion) test: an evaluation by XPS

The corrosion resistance of three different TiN coatings on iron (single TiN layer, Ti/TiN bilayer and Ti/TiN/Ti/TiN multilayer) subjected to a salt (ammonium sulphate and sodium chloride) fog spray (Prohesion) test has been investigated by means of x-ray pbotoelectron spectroscopy (XPS). The relative intensities of the Fe 2p and 0 1s signals in the XPS spectra of the corroded samples increase with their extent of degradation. The results show that the corrosion resistance of these coatings decrease in the order bilayer > multilayer > single layer.

Indirect oxidation of ethylene glycol by peroxide ions at Ni0.3Co2.7O4 spinel oxide thin film electrodes

Abstract Films of mixed valency oxides Ni x Co 3− x O 4 (1≥ x ≥0.1) were studied in alkaline solutions for the indirect oxidation of ethylene glycol (EG) by peroxide anions HO 2 − resulting from the cathodic reduction of O 2 . It was found that the electrocatalytical activity of the oxides correlated to nominal Co 3+ /Co 2+ content ratio in the spinel structure and that the oxide Ni 0.3 Co 2.7 O 4 , which presents the highest Co 3+ /Co 2+ ratio, was the most effective in the series.

Ni0.3Co2.7O4 spinel particles/polypyrrole composite electrode: Study by X-ray photoelectron spectroscopy

In this work we have studied the multilayered polypyrrole/oxide composite electrode on glassy carbon having the structure GC/PPy/PPy(Ni0.3Co2.7O4)/PPy, in which the spinel oxide Ni0.3Co2.7O4 is known to be an electrocatalyst of the oxygen reduction reaction in alkaline medium. The successive GC/PPy, GC/PPy/PPy(Ni0.3Co2.7O4) and GC/PPy/PPy(Ni0.3Co2.7O4)/PPy parts of the electrode were examined by X-ray photoelectron spectroscopy. The results indicate that the electronic structure of the PPy is independent of the thickness of the PPy used to prepare the electrodes. The XPS data also show that cobalt is present in both divalent and trivalent states. The PPy doping degree by Cl− ions (in terms of the Cl−/N) and the oxide/PPy mass ratio observed by XPS were 19 and 4.5%, respectively.

Influence of weathering on the sulphur removal from coal by pyrolysis

Abstract In this paper evidence of the negative effect of weathering on the sulphur removal by pyrolysis is reported. The study of the evolution of sulphur forms during the pyrolysis of a weathered coal has been conducted by chemical analysis, transmission Mossbauer spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis. This study shows that in the pyrolysis of weathered coals some special chemical changes occur when compared with the pyrolysis of unweathered coals. In particular, no accumulation of organic sulphur in chars has been observed, however, inorganic iron sulphates formed by the oxidation of pyrites are decomposed above 500°C and yield complex sulphides which accumulate in chars, decreasing the efficiency of the desulphurization. These sulphides, because of their unreactivity, cannot be determined completely by chemical analysis, which implies an overcalculation of organic sulphur when calculated by difference.

Mössbauer study of the corrosion behaviour of pure iron and weathering steel under a wet-dry cycle

Mossbauer spectroscopy (MBS) and X-ray diffraction (XRD) have been used to establish the composition of the rust layer formed on weathering steel and pure iron under several wet-dry cycles in a SO2-polluted atmosphere. FeSO3−3H2O, FeSO4−4H2O, and poorly crystalline ferrihydrite were identified as the only corrosion products. The Mossbauer spectrum of FeSO3−3H2O is reported.

Surface spectroscopic study of the corrosion of ultrathin 57Fe-evaporated and Langmuir–Blodgett films in humid SO2 environments

Integral conversion electron Mossbauer spectroscopy (ICEMS), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) have been used to carry out a comparative study of the corrosion resistance against humid SO2-aggressive environments of ultrathin 57Fe films. These films, having a thickness ≤ 2.5 nm, have been prepared by evaporation of 57Fe under vacuum and by 57Fe coating by a Langmuir–Blodgett (LB) technique on SiO2/Si wafers. The results have shown that the corrosion resistance of the evaporated films is similar to that of massive Fe. However, the LB films show a remarkably higher corrosion resistance. Thus, although the Fe films prepared by evaporation have been completely corroded after 6 h of exposure to the deleterious environment, the LB films remain unaltered even after 18 h of exposure to the same aggressive conditions. The higher corrosion resistance of the LB films appears to be related to the existence of a thin surface layer containing Si, Fe2+ and Fe3+ formed on top of the Fe metal film during the thermal treatments subsequent to the LB deposition. Copyright

Corrosion of weathering steel and iron under wet-dry cycling conditions: Influence of the rise of temperature during the dry period

The effect of a dry-hot period on the SO2 corrosion of weatherig steel and pure iron under wet-dry cycling was investigated. Corrosion products were identified by Mössbauer spectroscopy and X-ray powder diffraction. The formation of an intermediate corrosion layer of spm α-FeOOH only on weathering steel was the most significant result.

Corrosion studies of iron and its alloys by means of57Fe Mössbauer spectroscopy

Some of the advantages and limitations of Mössbauer spectroscopy when used in corrosion research are shown by using three examples taken from the work of the authors on (i) the passive layer of iron, (ii) the corrosion of weathering steels by SO2-polluted atmospheres and (iii) the performance of rust converters.

The corrosion of weathering steel by SO2 polluted atmospheres at its very early stages

CEMS was used in conjunction with AES to study the protective film formed on a weathering steel by exposure to a highly SO2-polluted atmosphere. Ferrous species (sulphite) and ferric oxyhydroxides (ferrihydrite and α-FeOOH) were identified as corrosion products. From the correlation of CEMS and AES results the evolution with time of the different compounds is obtained, and a possible reaction sequence is outlined.