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The interfacial properties of epoxy composites reinforced with a single, plasma-treated fibre of either poly(p-phenyleneterephthalamide) (PPTA) or poly(p-phenylenebenzobisoxazole) (PBO) have been investigated with a focus on evaluating the effect of two non-oxidative (He and N2) microwave plasma treatments on interfacial adhesion properties. Tensile testing of single filaments revealed that their tensile strength does not diminish with the plasma treatments, despite the fact that their surface properties have been both physically and chemically modified. Interfacial characterisation by Raman spectroscopy indicated that the quality of adhesion was substantially enhanced following exposure of the fibres to microwave plasma treatment in either pure helium or pure nitrogen flows for just one minute. Such improvement was higher than that attained when O2 was used for blowing the plasma, under the same operational conditions. Moreover, no swelling effect was observed by AFM after exposure of the He or N2 plasma-treated fibres to ambient conditions for as much as 24 h.

[Objective] To characterize children, adolescents and young adults infected with HIV/hepatitis C virus (HCV) vertically or before age of 18 years and living in Europe regarding mode of acquisition, HCV genotype, clinical status and treatment., [Design] Retrospective, cross-sectional study using pooled data from 11 European paediatric HIV cohorts., [Methods] Patients aged more than 18 months and less than 25 years, with HIV/HCV acquired vertically or in childhood, were included. Anonymized individual patient data were collected using a standard protocol and modified HIV Cohorts Data Exchange Protocol., [Results] Of 229 patients included, 142 (62%) had vertically acquired infection. Median age at last follow-up was 16.2 years. Most children had HCV genotype 1 (101/184, 55%) or 3 (57/184, 31%). One-fifth (46/214) had a previous AIDS diagnosis (data missing on prior AIDS diagnoses for 15). At their last clinic visit, 70% (145/208) had no/mild immunosuppression (Centers for Disease Control and Prevention stage 1), and 131 of 179 on antiretroviral therapy had undetectable HIV RNA (assay thresholds varied from, [Conclusion] The high proportion of patients with progressive liver disease underscores the need for close monitoring and earlier and more effective HCV treatment., This work was supported by funding from the EU Seventh Framework Programme (FP7/2007–2013) under EuroCoord grant agreement [no. 260694] and additional funding from Janssen.

The effect of nitrogen and oxygen plasma surface treatments on the compressive strength of PBO fibers has been studied. To this end, the nucleation and propagation of compression-induced kink bands was carefully monitored by means of in situ bending tests inside a scanning electron microscope. The micromechanisms of deformation were identical irrespective of fiber surface condition (either as-received or modified by plasma) but the critical stress necessary to induce irreversible damage in compression in the nitrogen-plasma treated fibers was 40% higher than in the as-received fibers. This improvement occurred without any reduction in the fiber tensile properties. The source of this behavior is discussed in the light of the morphological and chemical changes induced by the plasma treatments on the fiber surface, as studied by AFM and XPS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A combination of 57Fe-Mossbauer spectroscopy and X-ray Powder Diffraction analysis has been employed to study modifications in chemical and mechanical stability occurring in a cordierite burner aged under combustion conditions which simulate the working of domestic boilers. Mossbauer study shows that Fe is distributed into the structural sites of the cordierite lattice as Fe2+ and Fe3+ ions located mostly at octahedral sites. Ferric oxide impurities, mainly hematite, are also present in the starting cordierite material accounting for ≅40% of the total iron phases. From Mossbauer and X-ray diffraction data it can be deduced that, under the combustion conditions used, new crystalline phases were formed, some of the substitutional Fe3+ ions existing in the cordierite lattice were reduced to Fe2+, and ferric oxides underwent a sintering process which results in hematite with higher particle size. All these findings were detected in the burner zone located in the proximity of the flame and were related to possible chemical reactions which might explain the observed deterioration of the burner material.

We report on the corrosion behavior of thin films, prepared by dual ion beam sputtering (DIBS), containing different concentrations of γ'-and e-iron nitride phases. When deposited on Si wafers, the film containing almost equal amounts of γ'-Fe 4 N and e-Fe 3-x N phases shows the highest corrosion resistance. When deposited on iron substrates, all the films show almost total chemical degradation. We attribute this to the open microporosity of the different films deposited.

Metabolic syndrome (MetS) is considered an independent risk factor for developing cardiovascular disease. It is well known that the prevalence of metabolic disorders have increased in pediatric HIV-infected children. The objective of this study is to assess the prevalence and characteristics of MetS in HIV-infected children and adolescents in Spain.A cross-sectional multicenter study in 152 patients from the pediatric cohort of the Spanish AIDS Research Network (CoRISpe) was performed. MetS was defined according to the new International Diabetes Federation (IDF) diagnostic criteria and the modified National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) criteria. Measurements included anthropometry, waist circumference, blood pressure, fasting lipids, glucose and insulin and lipodystrophy assessment. Demographic, clinical, immunological, virological and antiretroviral therapy data were obtained from the Network database.An abnormally low high-density lipoprotein-cholesterol level was the most prevalent disturbance (21.05%) found. Three patients met IDF criteria for MetS (1.97%), and MetS was significantly associated with lipohypertrophy (P=0.029) in the analysis. When the modified NCEP-ATP III criteria were used, the prevalence of MetS was 5.92% (9 patients), and MetS was significantly associated with Tanner stage ≥2 (P=0.041), lipohypertrophy (P=0.001) and higher Z scores for weight and body mass index (P=0.002 and P0.001). Insulin resistance was observed in 17 patients (11.18%) and was associated with MetS (as per the modified NCEP-ATP III criteria) (P=0.03) and lower high-density lipoprotein-cholesterol values (P=0.036).The prevalence of MetS in our cohort was 1.97% or 5.92%, depending on the diagnostic criteria used. MetS should be actively assessed, particularly in children who show lipohypertrophy.

Two Fe–Ce catalysts were prepared by wet impregnation of Ce onto iron oxyhydroxide (FeOOH) and hematite iron oxide (α-Fe2O3), respectively. Their performance in the Fischer–Tropsch (FT) synthesis was investigated and compared with that obtained with a Ce-free α-Fe2O3 catalyst. It was observed that the behavior of the different catalysts changed along the course of the FT reaction. The catalysts were tested for different periods of time, carefully passivated, recovered from the reactor and characterized by different techniques. The FT activity of the Ce-loaded and Ce-free catalysts decreased initially, but at a certain point the catalytic activity started to increase. The time needed to reach this inflection point depended on the catalyst composition, being shorter for the Ce-promoted catalysts. The catalytic activity of the Ce-free catalyst increased when the Fe3C species were transformed into χ-Fe2.5C, which are suggested to be the carbide phase present when polymerized carbon species (Cβ) are formed. The addition of Ce to the iron oxyhydroxide developed solids with a higher BET surface area. Besides, these samples displayed a higher FT activity at long time-on-stream (TOS). Moreover, Ce addition also facilitated the formation of the Cβ species previous to the evolution of Fe3C into χ-Fe2.5C, and therefore, promoted the FT synthesis reaction.

Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems.

Two series of Fe−Ce catalysts were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and physical mixing of pure Fe and Ce precursors. Evidence of the presence of a chemical interaction between Fe and Ce was found in the calcined state of the coprecipitated catalysts. Such evidence was obtained with different techniques. The Fe−Ce interaction occurs through the formation of hematite-like and cubic ceria-like solid solutions. In the hematite-like solid solution, Ce cations are dissolved in the hematite structure, whereas in the cubic ceria-like solid solution Fe cations are dissolved in the ceria structure. Such interactions were absent in the samples prepared by the physical mixing. It is suggested that the Fe−Ce interaction present in the calcined state results in a strong Fe−Ce interaction in the final catalyst that defines their better catalytic properties. When tested in the Fischer−Tropsch synthesis of hydrocarbons from CO + H2 gas mixtures, the coprecipitati...

The Mn–Li ferrite system Li1−0.5xFe1.5x+1Mn1−xO4 (x = 1, 0.8, 0.6, 0.4, 0.2) has been studied by means of X-ray diffraction, Mossbauer spectroscopy and Mn K- and Fe K-edge XANES/EXAFS. All the samples show the spinel-related structure with the lattice constant a gradually decreasing between a = 0.8310 nm (x = 1) and a = 0.8301 nm (x = 0.2). Mossbauer and Fe K-edge XANES/EXAFS results have shown that the oxidation state of Fe is +3 and that the fractions of Fe3+ ions occupying the octahedral and tetrahedral sublattices do not change significantly along the series. Mossbauer data recorded under applied magnetic field indicate the existence in the Mn-containing samples of canted spin structures for the Fe3+ ions on both the tetrahedral and octahedral sites, the canting angle being larger for the octahedral sublattice. Mn K-edge XANES and EXAFS have shown Mn to be present as Mn3+ and Mn4+ and to occupy only octahedral sites. The XANES/EXAFS results have also shown that the Mn4+/Mn3+ ratio increases with increasing Li/Mn content. The results indicate that as the extent of Li/Mn insertion increases the new inserted Li+ ions occupy tetrahedral sites and that some of the Li+ ions initially occupying octahedral sites are also driven into tetrahedral positions.

10 pages (final publisher version), 23 pages (attached post-print version)., Two different types of ancient bricks (12th to 14th centuries) collected from historical buildings of Toledo (Spain) were characterised by optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectrometers (SEM/EDS), electron probe microanalysis (EM), X-ray diffraction (XRD), differential thermal analysis (DTA) and 57Fe-Mössbauer spectroscopy. Physical properties such as water absorption and suction, porosity, density and compression strength were also determined. Several minerals found in the brick matrix, such as garnet, let us infer raw material sources; calcite, dolomite, illite and neoformed gehlenite and diopside phases, on temperature reached in firing; secondary calcite, on first cooling scenarios; and manganese micronodules, on late pollution environments. XRD and DTA of original and refired samples supply information about firing temperatures. Additional data on firing conditions and type of the original clay are provided by the Mössbauer study. Physical properties of both types of bricks were compared and correlated with raw materials and fabric and firing technology employed. The physicochemical characterisation of these bricks provides valuable data for restoration purposes to formulate new specific bricks using neighbouring raw materials., The authors are especially indebted to Josefo Bedoya, technician of the Museo de Ciencias Naturales (Madrid), who took the beautiful SEM microphotographs for this work and was killed in a car accident during the preparation of this manuscript. We are also grateful to Carlos Sánchez (Faculty of Chemistry Sciences, Ciudad Real) for the XRD analyses. The Spanish project MCYT IFD 1997-0561 and agreement CICYT-JCCM (2002) supported the work.

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.

Oxides of compositions Li(1−0.5x)Fe(1.5x+1)Mn(1−x)O4 (0≤1−x≤1) with a spinel structure have been characterized by XRD analysis and Mossbauer spectroscopy. The surface properties of the materials have been studied by OCP, pHz and XPS measurements. The influence of the substitution of Fe by Mn on the electrocatalytic activity of the electrodes has been analyzed in terms of Tafel slopes and proposed cationic distribution. The oxygen evolution reaction depends on both OCP and pHz, and it is very sensitive to the iron/manganese ratio in the octahedral sites of the spinel structure.

The compound NiCo2O4, with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of +3.5 and +2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo2O4 of {Ni3+0.1Co2+0.9}tet[Ni3.5+0.9Co2.5+1.1]octO4. This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co3+ and Ni3+. The surface of NiCo2O4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co2+, Co3+, Ni2+, Ni3+ and, probably, Ni4+.

In this paper results are presented on the corrosion resistance against SO2-polluted atmospheres of ultrathin Fe layers (

The bulk structural properties of the nickel cobaltite, NiCo2O4, prepared by the thermal decomposition of carbonates, sol–gel methods, and the decomposition of hydroxides, have been examined by X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (EXAFS and XANES). The results indicate, as expected, that Ni occupies the octahedral sites of the spinel structure while Co occupies both tetrahedral and octahedral sites. The XANES and EXAFS data are compatible with the existence of Ni2+ and Ni3+. The structural data indicate that Co is present as Co2+ and Co3+.The bulk cation distribution appears to be dependent on the synthesis procedure. The results of the surface examination by X-ray photoelectron spectroscopy (XPS) show that the surface composition is different from the nominal bulk composition and also varies with the preparative method. All the XP spectra indicate the presence of Ni2+ and Ni3+, their relative concentrations being noticeably dependent upon the synthesis method used. In contrast, the Co XP spectra recorded from all samples are very similar and indicate the presence of both Co2+ and Co3+.

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 © 2000 John Wiley & Sons, Ltd.

In this paper we address the question of how telecommunications affect economic growth, by estimating the effect of direct investment in telecommunications infrastructures on aggregate output, employment, and investment in Spain. In contrast with previous studies, the problem is analyzed in a dynamic multivariate framework which allows for explicit consideration of feedbacks among all the variables. We find significant effects of the investment in infrastructures of telecommunications on aggregate output, employment and investment which extend for several years. This might justify a policy for stimulating investment in this sector.

The processes involved in the utilization of coal are affected by the minerals contained in it. Due to the presence of iron as a major constituent of coal mineral matter, and to the fact that the iron minerals, especially pyrite, and their transformation products play an important role in coal uses, 57Fe-Mossbauer spectroscopy appears as an attractive tool in coal research. Mossbauer studies related to the characterization of iron phases, coal oxidation and quantitative determination of pyritic sulphur are discussed in this work.

The objective of this paper is to evaluate the short- and long-term effects of public investment in infrastructure on aggregate output, labour and capital formation in the private sector. The problem is analysed in a dynamic multivariate framework, which allows for explicit consideration of feedback among all the variables. This approach generalizes the current literature, which relies on a single-equation model to estimate production functions and implicitly assumes the absence of feedback relationships. For the Spanish economy, our results suggest positive long-term effects of public investment on the private sector variables.

The fundamentals of Mossbauer Spectroscopy in the backscattering mode are given. The techniques used for the different backscattered particles and energies, and the experimental difficulties and advantages of each technique are discussed.

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+.

Mossbauer spectroscopy has been used extensively in surface studies. The different experimental approaches to derive surface information from this technique are reviewed.

The characterization of an iron-containing natural zeolitic sample from the deposit of Tasajeras (Cuba) has been carried out by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS),57Fe Mossbauer spectroscopy and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results show that iron is mainly located (ca. 96%) as Fe3+ in an octahedral site of the clinoptilolite framework. No evidence of tetrahedrally coordinated Fe3+ was found. The remaining 4% Fe is located as Fe2+ in an extraframework octahedral site, probably as a solvated ion, within the clinoptilolite structure.

Within a cooperative program for the elaboration of a Latin American Map of Atmospheric Corrosion, weathering steel and mild steel samples were exposed to the Antarctic atmosphere and the corrosion products analyzed by ICEMS, XPS and XRD. Superparamagnetic α-FeOOH was the main corrosion product after 24 h of exposure. Cl− ions are found on the surface of the corroded samples by XPS.

Some of the advantages and limitations of Mossbauer 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 setting up and updating of a Mossbauer laboratory imply the acquisition and assembling of different units. Guidelines concerning either the construction or the acquisition of the various parts which compose a Mossbauer spectrometer are given in this paper.

Fresh and naturally weathered coal samples from the same seam as well as the former one submitted to artificial oxidation treatments were studied by Mossbauer spectroscopy to examine the effect of coal oxidation conditions on the transformations of iron minerals. It was found that illite, pyrite and siderite are converted into jarosite and goethite in a natural environment, whereas only a small fraction of Fe2+ from pyrite was oxidized to Fe3+ under laboratory conditions, even after heating in air to 468 K. It is concluded that artificial oxidation experiments hardly reproduce the conditions met by coal when submitted to natural weathering.

Lithium−manganese ferrite LiFeMnO4 was prepared using two different methods: a conventional ceramic high-temperature solid-state reaction technique (Cer) and thermal decomposition of metal nitrate salts (NTD). The characterization of the compounds was carried out by SEM/EDX, XRD, XPS, Fe K- and Mn K-edge XANES, and Mossbauer spectroscopy. Both Cer and NTD LiFeMnO4 samples have the nominal expected Fe/Mn atomic ratio and show a homogeneous morphology, but they exhibit different particle sizes. Fe K-edge XANES and Mossbauer spectroscopy results show that the oxidation state of Fe ions is +3 in both samples, whereas the Mn K-edge XANES data indicate that the bulk average Mn oxidation state is +3 for the NTD sample and close to +4 for the Cer one. Thus, to maintain the charge neutrality, the NTD sample has to be nonstoichiometric in oxygen with a composition close to LiFeMnO3.5. The Mn 3s XPS data indicate that the average surface oxidation state of Mn is also lower in the NTD sample. The results suggest the ...

Mossbauer spectroscopy was used to determine the iron-containing minerals that remained in two different Spanish subbituminous coals after acidic treatments. Spectra were taken before and after treatments of both coals with HCl and HCl followed by HF. Pyrite, jarosite and Fe2+-clay were the main iron mineral constituents of the untreated samples. After the treatments significant changes in the relative concentration of these species were noticed. The weakness of the used demineralization procedures is discussed.

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 Mossbauer 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.

La dosis de diálisis administrada influye en la supervivencia de los pacientes, siendo deseable alcanzar un Kt/V óptimo. Diferentes estudios demuestran que existe una buena correlación entre el Kt medido por dialisancia (sin necesidad de extracciones sanguíneas) y el Kt/V. El objetivo de este estudio prospectivo fue comparar la medición de la dosis de diálisis por ambos métodos (Kt y Kt/V) en nuestra población en hemodiálisis, así como aquellos factores relacionados con la técnica que influyen en la dosis de diálisis alcanzada. Se ha estudiado a 131 pacientes. No se aprecian diferencias signifi cativas en el Kt en función del sexo mientras que el Kt/V se muestra como significativamente mayor en las mujeres (1,93 ± 0,23) que en los hombres (1,59 ± 0,25). Mientras que en el Kt las diferencias son significativas en función del acceso vascular no lo son para el Kt/V. En la dosis de diálisis en función del tipo de hemodiálisis, no se aprecian diferencias significativas en Kt/V entre los que reciben tratamiento con HD convencional y los que lo hacen con hemodiafiltración on-line, mientras que el 90% de los pacientes en hemodiafiltración on-line alcanzan un Kt óptimo frente a un 45,5% en HD convencional. La monitorización continua de la dosis de diálisis mediante la medición del Kt por dialisancia iónica permite discriminar mejor a los pacientes en situación de infradiálisis que la determinación del Kt/V.

Conversion electron Mossbauer spectroscopy (CEMS) has been used as a standard technique since details for the construction of appropriate electron gas counters were reported. In this paper after a short description of physical bases of CEMS, the methodological aspects of this technique are outlined.

ICEMS, XPS, XRD, and AES have been used to study the corrosion layers formed on two metallic glasses, Fe80B20 and Fe40Ni40(MoB)20 (2605 and 2826 MB, Allied Company), exposed to an SO2-polluted humid atmosphere. The iron-containing corrosion products are the same found for pure iron in the same environment, but different relative concentrations were clearly evidenced by ICEMS results. Elemental sulphur, Ni(OH)2, and B(OH)3, the latter enriched at the surface, were found by XPS, XRD, and AES.

Samples of pyrite-rich brown coal from As Pontes and Meirama coalfields (Spain) were oxidized either by air at atmospheric pressure or by a cool oxygen plasma generated by radiofrequency activation. Despite the very different nature and characteristics of the oxidizing media, in both cases the RT Mossbauer spectra were easily fitted to two doublets, whose parameters matched those of pyrite and jarosite (hydrated iron (III) sulphate). The extent of pyrite oxidation to jarosite was monitored by the relative spectral areas of pyrite and jarosite doublets. Both, air and plasma, oxidized pyrite to the same extent and in a similar way, in contrast to coal organic matter, which was scarcely modified by air but completely oxidized by the plasma at the same temperature (ca. 423 K). The incomplete oxidation of pyrite by plasma is attributed to the action of a thin calcium sulphate layer which hinders the access of activated oxygen to small pyrite crystals.

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.

Supported iron catalysts were prepared by adsorption of potassium hexacyanoferrate (II) complex onto acid-modified alumina surfaces. The impregnated preparations were reduced with hydrogen without a calcination step and tested in the ammonia synthesis reaction. At 583 K and a total pressure of 76 atm of a stoichiometric mixture (H2-to-N2 molar ratio = 3:1), the rate of formation of ammonia increased with increasing iron content of the catalyst, viz., decreasing iron dispersion (as measured by nitric oxide chemisorption). Several iron species were detected on reduced catalysts by Mossbauer and infrared spectroscopy. The Mossbauer spectra all indicated a slight contribution of a magnetic component and three overlapping doublets (two of Fe2+ and one of Fe3+). The infrared spectra of adsorbed nitric oxide revealed the presence of Fe2+ and eventually Fe0 sites. On Fe0 centres, the nitric oxide is adsorbed as a mononitrosyl whereas Fe2+ centers of two configurations lead either to a dinitrosyl (NO)2 or a mononitrosyl. It was also shown by X-ray photoelectron spectroscopy that, during the air-drying step of the catalyst precursors, a fraction of the cyanide ligands are removed and iron is simultaneously oxidized to Fe3+. This latter ion strongly interacts at the Al3+ vacancies resulting from acid treatment of the carrier before the anchorage of the hexacyanoferrate (II) complex.

A series of Fe-Ce mixed oxides (95 atom % Fe-5 atom % Ce) has been prepared by different methods: coprecipitation, impregnation, and physical mixture of Ce and Fe oxides. These solids have been tested in the Fischer-Tropsch synthesis. The characterization of the catalytic precursors was carried out by X-ray diffraction (XRD), Raman, Mossbauer, and X-ray photoelectron (XPS) spectroscopic techniques. When the preparation method ensures a microscopic contact between Fe and Ce cations in the solid, several types of Fe-Ce interactions are present in the calcined solids. The interactions take the shape of Fe-O-Ce bridges that can exist either in the hematite-like solid solution or in the interphase between the Fe oxide covered by microcrystals of Ce oxide. In the case of the hematite-like solid solution, Ce(IV) cations are dissolved in the alpha-Fe2O3 network. The promotion by Ce of the catalytic properties observed in the final catalysts can be directly related with the detection of these Fe-O-Ce bridges in the calcined solids. The Ce promotion results in a larger yield to hydrocarbons, a higher production of olefins, and a higher selectivity to medium and large chain hydrocarbons (larger than six carbon atoms). It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-Ce bridges developed in the parent calcined samples.

Mossbauer Spectroscopy is a very useful and well-known technique for the study of mainly Fe-containing materials. Most of the measurements with this spectroscopy are performed in the transmission mode, while for the study of surfaces the back-scattering mode is the preferred option. Backscattered radiation contains “resonant” and “nonresonant” radiations, the first originated as a consequence of the relaxation process, which follows resonant absorption (Mossbauer Effect), being the signal, and the second being due to the photoelectric and Compton interactions, the noise. The relaxation process is rather complex and involves both nuclear and atomic relaxations, producing conversion and Auger electrons, and gamma and X-ray photons, all of them of well defined energies, whose probability to leave the surface is related to their nature, energy and track within the solid. The detection of any of these emitted radiations provides a valuable tool to obtain spectra with varying depth resolution.

The characterization of the corrosion products formed on carbon steel SAE 1070 after one year exposure to the open atmosphere in the Antarctic (polar climate) and in Easter Island (subtropical climate) has been carried out by means of transmission 57Fe Mossbauer spectroscopy. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The major constituent of the rust formed in the Antarctic environment is goethite (α-FeOOH). The Antarctic samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe2O3). In the case of the Easter Island samples, lepidocrocite is the major constituent of the corrosion layers. The rust formed under the Easter Island environment also contains large amounts of ferrihydrite and, in a lesser proportion, goethite and maghemite. (C) 2000 Elsevier Science Ltd. All rights reserved. | The characterization of the corrosion products formed on carbon steel SAE 1070 after one year exposure to the open atmosphere in the Antarctic (polar climate), and in Easter Island (subtropical climate) has been carried out by means of transmission 57Fe Moessbauer spectroscopy, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The major constituent of the rust formed in the Antarctic environment is goethite (α-FeOOH). The Antarctic samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe2O3). In the case of the Easter Island samples, lepidocrocite is the major constituent of the corrosion layers. The rust formed under the Easter Island environment also contains large amounts of ferrihydrite and, in a lesser proportion, goethite and maghemite., Financial support from the Fundación Andes (project C-10810/2), the Spanish CICYT (projects MAT93-0165 and PB96-0851) and both the CSIC and the Universidad de Chile are gratefully acknowledged.