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Digital.CSIC (162.855 recursos)

Repositorio institucional del Consejo Superior de Investigaciones Científicas. Digital.CSIC es un depósito de documentos digitales, cuyo objetivo es organizar, archivar, preservar y difundir en modo de acceso abierto la producción intelectual resultante de la actividad investigadora del CSIC.

(CENIM) Artículos post-print

Mostrando recursos 1 - 20 de 28

  1. Steel corrosion behaviour in carbonated alkali-activated slag concrete

    Aperador, Willian; Mejía de Gutiérrez, R.; Bastidas, David M.
    Steel bars embedded in an alkali-activated slag (AAS) concrete were exposed (after curing for 28 days) to an accelerated carbonation test (3% CO2, 65% relative humidity (RH), and 25 °C temperature) and a laboratory environment (0.03% CO2, 65% RH, and 25 °C). Ordinary Portland cement (OPC) was also tested for comparative purposes and exposed to identical experimental conditions. The corrosion behaviour of uncarbonated and carbonated AAS and OPC concretes was tested for different times, performing corrosion potential, linear polarization resistance, and electrochemical impedance spectroscopy measurements. Corrosion products were analysed using the Mössbauer technique. The main corrosion products found were magnetite...

  2. Influence of conductivity on cathodic protection of reinforced alkali-activated slag mortar using the finite element method

    Montoya, R.; Aperador, Willian; Bastidas, David M.
    Cathodic protection (CP) is considered to be the only rehabilitation method for chloride-induced rebar corrosion in reinforced concrete structures. The protection current distribution depends on several parameters, such as the geometry and number of rebars and the concrete resistivity. In order to investigate the influence of concrete resistivity on the possibilities and limitations of rebar protection, this paper presents a numerical approach based on the finite element method (FEM) in conjunction with laboratory results to determine its impact on the CP of alkali-activated slag mortar. An ordinary Portland cement was also tested for comparative purposes. © 2009 Elsevier Ltd. All...

  3. Laminar composites of steel and zinc matrix: Charpy tests

    Vázquez, Antonio; Damborenea, Juan de
    The preparation of a laminar composite with steel reinforcing sheets in a zinc matrix is described. The results of a Charpy test normal to the sheet plane are presented. With the same steel thickness the impact energy grows with the number of sheets. A mechanism of delamination after the impact test is proposed.

  4. Evolution of microstructure during low temperature superplastic deformation of bulk nanostructured Ni-Cr-Fe-Nb superalloy

    Valitov, V. A.; Mukhtarov, S. K.; Zhilyaev, A. P.; Ruano, Oscar Antonio
    Ultrafine-grained and nanocrystalline structure have been obtained in Ni-Cr-Fe-Nb based alloy (INCONEL® 718) by multiple isothermal forging. The ultrafine-grained and nanostructured samples demonstrated low temperature (7=700 °C) superplastic behavior. Nanostructured alloy showed larger uniform elongation and reduced cavitation than those of Inconel 718 with microcrystalline structure. Electron backscatter diffraction was employed to reveal characteristics of structure, second particles distribution and grain boundary statistics. © 2010 Advanced Study Center Co. Ltd.

  5. Failure analysis of prestressed anchor bars

    Elices, M.; Valiente, Andrés; Caballero, L.; Iordachescu, M.; Fullea, J.; Sánchez-Montero, J.; López, Víctor
    Three broken steel bars from a sewed crack in a dam are reported. The inspection of the fracture surfaces of the prestressed bars suggests that fractures were triggered by small cracks and by the inherent brittleness of the bars, as fracture toughness was about 40MPam 1/2. The analysis of the failures shows that the usual design requirements for prestressing bars fail to warn against brittle failures if some damage exists. Some recommendations, based on the concept of damage tolerance, are suggested to avoid similar unfortunate incidents. © 2012 Elsevier Ltd.

  6. Failure analysis of prestressed anchor bars

    Elices, M.; Valiente, Andrés; Caballero, L.; Iordachescu, M.; Fullea, J.; Sánchez-Montero, J.; López, Víctor
    Three broken steel bars from a sewed crack in a dam are reported. The inspection of the fracture surfaces of the prestressed bars suggests that fractures were triggered by small cracks and by the inherent brittleness of the bars, as fracture toughness was about 40MPam 1/2. The analysis of the failures shows that the usual design requirements for prestressing bars fail to warn against brittle failures if some damage exists. Some recommendations, based on the concept of damage tolerance, are suggested to avoid similar unfortunate incidents. © 2012 Elsevier Ltd.

  7. Soft x-ray absorption spectroscopy study of oxide layers on titanium alloys

    López, María Francisca; Soriano, L.; Palomares, F. Javier; Sánchez Agudo, M.; Fuentes, G. G.; Gutiérrez, A.; Jiménez, José Antonio
    Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide films formed after contact with air, both at room temperature and at 750 ◦C, on three titanium alloys. The alloys investigated were Ti–13Nb–13Zr, Ti–15Zr–4Nb and Ti–7Nb–6Al. Soft x-ray absorption spectra were taken at the Ti 2p and O 1s edges. The spectra corresponding to the room-temperature-oxidized samples are similar for the three alloys and show the presence of native oxide with a small metallic contribution. For the heat-treated samples, the alloying elements as well as element diffusion play a significant role in the formation of the oxide...

  8. Comparative study of the corrosion behavior of MA-956 and conventional metallic biomaterials

    Escudero Rincón, María Lorenza; López, María Francisca; Ruiz, J.; García-Alonso, M. C.; Canahua, H.
    In this work the corrosion behavior of a new biomaterial, the MA-956 superalloy, immersed in Hank's solution is evaluated. A comparison with conventional metallic alloys used as articular implants is established. To determine the corrosion behavior we employed electrochemical methods: evaluation of corrosion potential E(corr), electrochemical impedance spectroscopy (EIS), and anodic polarization curves. The corrosion resistance of the MA-956 superalloy preoxidized at 1100°C during 100 h is at least two orders of magnitude higher than for the other alloys. This satisfactory behavior is stationary with time. Also the probability of the appearance of the pitting corrosion process is very low....

  9. Surface analysis of a heat-treated, Al-containing, iron-based superalloy

    López, María Francisca; Gutiérrez, A.; García-Alonso, M. C.; Escudero Rincón, María Lorenza
    The surface composition of MA 956 superalloy both as-received and after four exposure times at 1100 °C has been investigated by energy dispersive x-ray spectrometry (EDX) and x-ray photoelectron spectroscopy (XPS). The passive layer of the as-received sample is mainly formed by Cr- and Fe-oxides. Heat treatment leads to the formation of an alumina layer on which small nodules grow. XPS spectra evidence the presence of titanium and yttrium oxides at the surface of the heat-treated samples, suggesting Y and Ti outward diffusion through the alumina layer. Iron and chromium oxides at the topmost surface layers are observed only for...

  10. X-ray photoelectron spectroscopy study of thiols adsorbed on Pt(111) with and without the presence of a copper monolayer

    Alonso, C.; López, María Francisca; Gutiérrez, A.; Escudero Rincón, María Lorenza
    The displacement of an electrodeposited Cu monolayer on Pt(111) single crystal by 2-mercaptopyridine (2-MP) and 4-mercaptopyridine (4-MP) has been investigated by XPS. The results indicate that the Cu adatoms are partially displaced by the 4-MP and completely displaced by the 2-MP. An analysis of the S 2p spectra of 2-MP and 4-MP adsorbed on Pt(111) both with and without the presence of a Cu monolayer reveals a small binding energy shift between 2-MP and 4-MP emissions. This effect is probably due to the formation of a surface chelate for 2-MP via bonding through both nitrogen and sulphur atoms. An additional...

  11. Chemical analysis of passive films on type AISI 304 stainless steel using soft X-ray absorption spectroscopy

    Bastidas Rull, José María; López, María Francisca; Gutiérrez, A.; Torres, C. L.
    X-ray absorption spectroscopy has beem employed to investigate the differences between passive films on type AISI 304 stainless steel produced by anodic polarization at two scan rates and four potential values. Cr LIII,II spectra show that in all cases a Cr2O3 film is formed at the surface. Fe and Ni signals have a mainly metallic lineshape with a possible small contribution from hydroxides, which is maximum for the polarization sample at the slowest scan rate and the maximum potential. Also for this sample a decrease in the Mn signal indicates Mn dissolution. | X-ray absorption spectroscopy has been employed to...

  12. Soft x-ray absorption spectroscopy study of electrochemically formed passive layers on AISI 304 and 316L stainless steels

    López, María Francisca; Gutiérrez, A.; Torres, C. L.; Bastidas Rull, José María
    The structure and composition of passive films electrochemically formed on AISI 304 and 316L stainless steels in a chloride-containing solution have been studied by soft x-ray absorption spectroscopy. Soft x-ray absorption spectra were taken at the oxygen Is edge and at the transition metals (Cr, Fe, Ni) 2p edges, making it possible to determine the main contributions to the passive film's composition. The soft x-ray absorption spectra at the Cr 2p edges indicate that in all cases the passive film is mainly formed by Cr2O3. Spectra at the Fe and Ni 2p edges exhibit no significant contribution of Ni and...

  13. Effect of mineral compounds in phosphoric acid polluted by sulphide ions on corrosion of nickel

    Guenbour, A.; Zeggaf, S.; Ben Bachir, A.; Escudero Rincón, María Lorenza; López, María Francisca
    The inhibiting effects of two mineral compounds on corrosion of nickel in phosphoric acid (H3PO4) polluted by sulfide ions (S2−) was studied using electrochemical and spectroscopic techniques. Electrochemical measurements showed addition of bentonite or phosphate mineral reduced the corrosiveness of H3PO4 polluted with S2− considerably. X-ray photoemission spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) showed these inhibitors did not incorporate into the passive film of the material and, therefore, did not induce any change in capacitance of the passive film. Results suggested the inhibiting effect stemmed from avoiding the adsorption of S2− ions on the nickel surface.

  14. Corrosion behaviour of FeAl-type intermetallic compounds

    López, María Francisca; Escudero Rincón, María Lorenza
    In this study, the corrosion behaviour of two different iron aluminides based on FeAl, with two different microstructures, in a chloride-containing solution (pH = 7.4), has been investigated using electrochemical techniques. Both materials were studied in as-received condition and also after heat-treatment at 1100°C for two hours. This thermal process was performed to generate an alumina layer on the intermetallic surface with the purpose of improving its corrosion resistance. The polarization resistance method and the electrochemical impedance spectroscopy reveal similar corrosion resistance values for all samples although the corrosion attack produced is different. This result indicates that for these intermetallic...

  15. Corrosion behaviour of amorphous Fe-Cr-Ni-(Si,P) alloys

    López, María Francisca; Escudero Rincón, María Lorenza; Vida, E.; Pierna, A. R.
    The passive layers formed spontaneously via air contact on the surface of amorphous Fe62 Cr10 Ni8 X20 (X = Si,P) alloys were studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The results for Fe62 Cr10 Ni8 Si20 showed the formation of a protective film, mainly consisting of oxidized chromium, that greatly enhanced the corrosion resistance of this alloy, whereas in Fe62 Cr10 Ni8 P20 the film was less corrosion resistant. To evaluate the influence of the passive layer composition on the corrosion resistance, standard electrochemical measurements on both alloys in 0.01 M HCl solution were performed. The...

  16. XPS study of the displacement of an electrodeposited Cu monolayer on Pt by mercaptopyridines

    Gutiérrez, A.; Alonso, C.; López, María Francisca; Escudero Rincón, María Lorenza
    The displacement of an electrodeposited Cu monolayer on polycrystalline Pt by 2- and 4-mercaptopyridine in solution has been investigated by XPS. The results indicate that, in both cases, the Cu adatoms are completely removed and substituted by mercaptopyridine molecules. An analysis of the S 2p spectra reveals a binding energy shift between adsorbed 2- and 4-mercaptopyridine, associated with the different electronic environment around the S atom in each case. An additional component, whose intensity correlates with that of the N-Pt component in the N 1s spectra, is assigned to S atoms in dimers, suggesting that N-Pt interaction decreases the probability...

  17. Synchrotron radiation photoemission study of the passive layers of heat treated Fe3Al-type alloy

    López, María Francisca; Gutiérrez, A.; García-Alonso, M. C.; Escudero Rincón, María Lorenza
    We report on a synchrotron radiation photoemission study of an Fe3Al-type alloy. The influence of different annealing treatments on the surface electronic structure has been investigated. The Al-2p photoemission spectra show slight differences among samples with a very small metallic Al component. From the Fe-3p and the valence band photoemission spectra, a higher surface Fe-content for the sample having a defective ordered B2 structure is observed. This finding is explained in terms of the bulk structure and the thickness of the passive layer. After determination of the surface composition of the samples, electrochemical experiments in Hank's solution have been performed...

  18. X-ray absorption and Auger electron spectroscopy studies of the quality of diamond thin films grown by the oxy-acetylene flame method

    Gutiérrez, A.; López, María Francisca; García, Ignacio; Vázquez, Antonio
    Diamond thin films grown by the oxy-acetylene flame method have been investigated by x-ray absorption and Auger electron spectroscopies. The quality of the films, defined as the ratio of diamond to non-diamond carbon, has been determined by using both techniques, giving values as high as 95% for the sample grown with the highest C2H2/O2 molar ratio (0.97). Values obtained by Auger electron spectroscopy are slightly lower due to the smaller probe depth of this technique as compared with x-ray absorption spectroscopy (5 Å in the first case against 50 Å in the latter), and to the higher non-diamond carbon content...

  19. XPS and Auger study of the radial variations of diamond thin films grown by the oxy-acetylene flame method

    García, Ignacio; Gutiérrez, A.; Vázquez, Antonio
    Free standing diamond thin films grown by the oxy-acetylene flame method have been investigated by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), The radial distribution of the sp2-hybridized carbon species on the films and, consequently, the film quality, have been determined. While XPS does not seem to be an appropriate technique to distinguish between very small variations in firm quality, an analysis of the Auger widths can explain the differences observed by scanning electron microscopy (SEM) and optical microscopy in the different regions of the samples.

  20. Effects of mercaptopyridines on the underpotential and overpotential deposition of copper on Pt(111)

    Salomón, A. B.; Gutiérrez, A.; López, María Francisca; Escudero Rincón, María Lorenza; Alonso, C.
    We present cyclic voltammetry studies of the under- and overpotential deposition of copper on a Pt(111) electrode in aqueous 0.50 M sulfuric acid solution in the presence and in the absence of adsorbed layers of 2- and 4-mercaptopyridine (2-MP, 4-MP). In general, the presence of adsorbed layers has been found to inhibit electrodeposition processes, suggesting very strong interactions between the adsorbates and the Pt(111) surface. 2-MP originates a higher degree of inhibition, which is ascribed to a stronger interaction probably due to the formation of a surface chelate via bonding through both N and S atoms. Studies have also been...

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