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The dramatic texture and microstructural changes observed in 6061Al-20vol%SiC metal matrix composite undergoing severe thermal cycles, under the absence and the simultaneous action of an external tensile stress, are studied. Under only thermal cycles (100–450 °C) homogenization and disorientation of the SiC whisker reinforcement and crystallographic texture randomization occurs. However, when a simultaneous tensile stress is applied, the whiskers rotate so that their long direction aligns with the tensile axes. Furthermore, a strong texture and large deformations (superplasticity), higher than 1000%, are achieved. These results are explained on the basis of the microscopic stress fields generated at the different microstructural scales (stresses of type II and type III) and well-known observation of dislocation generation at the SiC-metal interface during the cooling period of the cycles. We propose that moving dislocations (responsible of type III stresses) operate differently under the absence or the presence of the external stress. Under no stress, dislocation motion (occurring mainly during the heating period) is driven only by the type II internal stress. However, dislocation motion is improved when an external stress is applied, leading to texture changes and large elongations. Despite that a low external stress is applied, it overcomes the effect of the internal stresses for dislocation motion.

The effect of laser surface melting on the corrosion resistance of AZ31 Mg alloy in 0.1 M NaCl solution was investigated using different laser processing conditions (energy densities of 14 and 17 J cm). Laser treatment induced rough surfaces primarily composed of oxidized species of Mg. XPS analysis revealed that the surface concentration of Al increased significantly as a consequence of LSM. Electrochemical impedance spectroscopy showed that the laser treatment remarkably increased the polarization resistance of the AZ31 Mg alloy and induced a passive-like region of about 100 mV, as determined by potentiodynamic polarization. Analysis of the results obtained provide solid evidence that within the immersion times used in this study, LSM treatment increased the corrosion resistance of AZ31 Mg alloy under open circuit conditions and anodic polarization.

Electrochemically reduced graphene oxide (ErGO) films on a biomedical grade CoCr alloy have been generated and characterized in order to study their possible application for use on joint prostheses. The electrodeposition process was performed by cyclic voltammetry. The characterization of the ErGO films on CoCr alloys by XPS revealed sp2 bonding and the presence of C[dbnd]O and C[sbnd]O residual groups in the graphene network. Biocompatibility studies were performed with mouse macrophages J774A.1 cell cultures measured by the ratio between lactate dehydrogenase and mitochondrial activities. An enhancement in the biocompatibility of the CoCr with the ErGO films was obtained, a result that became more evident as exposure time increased. Macrophages on the CoCr with the ErGO were well-distributed and conserved the characteristic cell shape. In addition, vimentin expression was unaltered in comparison with the control, results that indicated an improvement in the CoCr biocompatibility with the ErGO on the material surface. The in vivo response of graphene and graphene oxide was assessed by intraperitoneal injection in wistar rats. Red blood cells are one of the primary interaction sites so hemocompatibility tests were carried out. Rats inoculated with graphene and graphene oxide showed red blood cells of smaller size with a high content in hemoglobin.

The role of the MgAl second phase on the anomalous HE and anodic dissolution of AZ31 and AZ91 Mg alloys was investigated. A passive-like behavior was exhibited by the MgAl phase with strong anomalous HE originating from local anodic regions where the passive film had broken down. The MgAl exhibited lower HE rates than the AZ Mg alloys during anodic polarization. Surface characterization confirmed that dissolution of MgAl in the AZ91 alloy only occurred above the E for the MgAl. Under anodic polarization, greater amounts of MgAl are beneficial for AZ Mg alloys durability, decreasing the Mg matrix dissolution rates.

Three newly synthesized Schiff base derivatives, sodium (E)-4-(nitrobenzylideneamino)-benzoate (SNBB), sodium (E)-4-(benzylideneamino)-benzoate (SBB), and sodium (E)-4-(hydroxybenzylideneamino)-benzoate (SHBB) were investigated as pitting corrosion inhibitors for 304 stainless steel in neutral 0.1 M NaCl. Potentiodynamic polarization evidenced major shifts in pitting potential to more positive values with increasing inhibitor concentration. The scanning vibrating electrode technique (SVET) imaged metastable pitting in 0.1 M NaCl, but not in the presence of the inhibitor, indicating that it prevented pit nucleation. The inhibition performance was established under anodic polarization conditions, because only minute local anodic activity due to metastable pit formation could be observed when the steel was exposed to SNBB-containing solution, whereas the metal would undergo pit propagation at the same potential in the inhibitor-free solution. X-ray photoelectron spectroscopy (XPS) analysis evidenced chromium enrichment at weak points (pores) of the passive film at anodic polarization condition where sudden release of Fe cations is possible. In this way, the SNBB molecules will migrate to these sites to react with the Fe ions and form a chelate compound which will deposit finally at those sites and plug them, whereas no effect occurred at the open circuit potential (OCP).

In this work, synthesis of copper/reduced graphene oxide composites to increase the electrical conductivity of copper matrix has been carried out. Pure copper particles were mixed with 0.28 wt%, 1.1 wt% and 2.5 wt% graphene oxide (GO) contents. Different reduction methods were chosen to synthetize the Cu/rGO composite material: chemical reduction with hydrazine, thermal treatment at 815 °C in argon atmosphere. Characterization of the Cu/rGO composite disks was carried out by optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Vickers Hardness and the electrical conductivity measured by Van der Pauw method of the Cu/rGO composites were analyzed. All the Cu/rGO disks showed lower hardness values than the Cu matrix. Microstructure of Cu/rGO composites is dominated by the presence of pores where GO agglomerates are accumulated and whose distribution and magnitude depends on the weight percentage of GO and the reduction process. Porosity percentage and pore size of Cu/rGO disks increase with GO content. Combination of chemical reduction with thermal treatment provides the most homogeneous microstructures with the smallest pore size and porosity percentage. Combination of both reduction treatments promotes more pathways for carrier transport within the reduced graphene oxide network structure, expanding areas of long-range conjugated structures and, consequently, increasing the electrical conductivity in the rGO/copper composites. Our research evidences that the Cu/rGO composites after chemical and thermal reduction increases the electrical conductivity, independently on the GO content, with respect to the pure copper matrix.

The article recently published in Electrochim. Acta [1] reported the results obtained by us about three main items: 1. The stability voltage window and working voltage window for the electrolytes Et4NBF4, Pr4NBF4 and Bu4NBF4 in combination with a microporous carbon monolith (Micro CM) and also with a mesoporous carbon monolith (Meso CM). 2. The specific capacitance associated with the anion BF4 - and the three cations Et4Nþ, Pr4Nþ and Bu4Nþ and their relative contributions to the total specific capacitance, the latter as measured in the three-electrode cell and the two-electrode one. 3. The comparison of the ratios of the specific capacitances of the anion and the three cations and the ratios of the surface areas deduced for pores with sizes larger than certain values, the latter ratio obtained from immersion calorimetry (for micro CM) and N2 adsorption isotherm/HS-2D-NLDFT (for meso CM). I think that the agreement between the ratios of the specific capacitances and the ratios of the surface areas pointed out the validity of the two techniques (immersion calorimetry and adsorption isotherms) for determining relative values of the surface areas. Moreover, the comparison of the capacitance ratios with the surface areas ratios allowed us the estimation of the minimum size of pore able to host the anion and the three cations as they are electro-adsorbed at the electric double layer. Because we were aware that different techniques for measuring the specific surface areas can lead to different values, only the last paragraph of the Results and Discussion section (page 128) dealt with the item of capacitance normalized by surface area, i.e. the capacitance normalized by the absolute values of the surface areas. The comments by T.A. Centeno points out that the surface areas obtained by immersion calorimetry can differ from the surface areas deduced from DFT on adsorption isotherms of CO2 and N2.We also observed that the surface areas deduced by HS-2D-NLDFT agreed better wit

Two step water-splitting cycles by using metal ferrites are considered as a clean and sustainable hydrogen production method, when concentrated solar energy is used to drive the thermochemical reactions. This process involves the reduction at very high temperature of the ferrite, followed by the water reoxidation to the original phase at moderate temperature, with the release of hydrogen. In order to decrease the temperature required to decompose the oxide, mixed ferrites of the type MFeO with spinel crystal structure have been examined. In this sense, ferrites with the partial substitution of Co and Ni for Fe appear as successful materials in terms of hydrogen production and cyclability. In this work, commercial Ni and synthetic Co ferrites have been subjected to two water splitting cycles. The solid products obtained after thermal reduction and water decomposition reactions have been chemically and structurally characterized by WDXRF, XRD, XPS and SEM techniques, in order to get a deeper understanding of the mechanisms controlling the water splitting process. This knowledge contributes to improve the process involved in thermochemical cycles and to understand the lower efficiencies (H/O) for Co ferrite thermochemical cycles in comparison with those corresponding to Ni ferrite.

In the present work, the characterization of Electrochemically Reduced Graphene Oxide (ErGO) films on a biomedical grade CoCr alloy has been performed. The direct electrodeposition process was carried out by means of two electrochemical techniques: chronoamperometry and cyclic voltammetry experiments, both taking into account the influence of oxygen in the solution. Characterization of the resulting ErGO films on CoCr alloys was carried out by SEM, AFM, Raman spectroscopy and XPS. Both electrochemical reduction procedures led to the deposition of graphene-based films on the CoCr surfaces after the partial removal of the oxygenated functional groups present in the graphene network of the starting material. The deconvolution of the XPS high-resolution C1s and O1s spectra mainly showed Csp2 bonding and the presence of CO and CO residual groups covering the CoCr surface. Moreover, the ErGO films that were stacked on the CoCr surfaces exhibited non-uniform thickness reaching values corresponding to the presence of 80 layers of the graphene material. In addition, Raman spectroscopy revealed a certain structural disorder in the ErGO films deposited by means of the different electrochemical techniques investigated. This fact was more evident on the film from the chronoamperometric experiments, as the fastest electrochemical reduction rate provided by the application of a high reduction potential (−2.1 Vvs. Ag/AgCl) could induce the development of defects in the resulting film, so the peaks corresponding to the CoCr substrate could be observed.

Three electrolytes with the same anion BF but different cation, EtN, PrN and BuN, are studied in combination with two binder-free carbon monoliths, one microporous and another mesoporous. The stability and working voltage window are measured. The former window broadens according to the trend BuNBF > PrNBF > EtNBF for the two monoliths. The latter window coincides with the stability voltage window for the mesoporous monolith but the trend is reversed to EtNBF> PrNBF> BuNBF for the microporous monolith. The specific capacitances associated with the cations and anions are separately measured. The specific capacitances follow the trend BF > EtN> PrN >BuN and are higher for the microporous monolith. From comparison of the ratios of the specific capacitances with those of the surface areas due to pores with sizes larger than certain values, the minimum size of the pores able to host the electro-adsorbed ions at the double layer is deduced; it results to be 0.56–0.58 nm for BF , 0.63–0.65 nm for EtN, 0.75–0.76 nm for PrN and 0.9–1 nm for BuN. The surface areas that are accessible and inaccessible to the four ions are estimated for the two monoliths. The better electrolyte/monolith combinations are discussed from a practical point of view.

Different mortar mixes using TiO2 P25 as photocatalyst have been prepared. The samples were characterized by UV–vis spectroscopy, X-ray photoelectron spectroscopy and Photoluminiscence spectroscopy. Also, determination of hydroxyl radicals and degradation tests of NOx under visible and UV light have been performed. The results obtained have allowed determining the band edges, Urbach energies and valence band tail sizes, directly related to the energy levels present in the TiO2-cement based materials. Therefore, the schema of the electronic structures of the reference TiO2-photocatalyst and the three TiO2-cement based samples have been constructed. The photocatalytic efficiency has been evaluated according to these energy levels, being able to conclude that in some cases, as the mortar with slags, the chemical composition seems to prevail over the effect of the optical parameter and electronic band structure.

The interaction of the physiological medium and living tissues with the implant surfaces in biological environments is regulated by biopotentials that induce changes in the chemical composition, structure and thickness of the oxide film. In this work, oxide films grown on CoCr alloys at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl have been characterized through overall and localized electrochemical techniques in a phosphate buffer solution and 0.3% hyaluronic acid. Nanopores of 10–50 nm diameter are homogeneously distributed along the surface in the oxide film formed at 0.7 V vs Ag/AgCl. The distribution of the Constant Phase Element studied by local electrochemical impedance spectroscopy showed a three-dimensional (3D) model on the oxide films grown at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl. This behaviour is especially noticeable in oxide films grown at 0.7 V vs Ag/AgCl, probably due to surface inhomogeneities, and resistive properties generated by the potentiostatic growth of the oxide film.

Phenomenon of gas triboemission has been used for characterisation of hydrogen content in construction steel under real-life conditions. The effect of surface layers on steel resulting from exposure to concrete pore solution, sea water, etc. on kinetics and behaviour of gas emission were investigated. The contribution to the gas emission from loose oxide layer was insignificant, but it enhanced the rate of gas emission because of more severe abrasion. For the samples with a dense layer both the layer and the base material contributed to gas emission. The results were qualitatively interpreted in the frameworks of a phenomenological model that describes triboemission as convolution of characteristic function of MSGE and the rate of new material involvement in deformation process.

To characterize the degradation mechanisms of silicate glasses in river and marine aquatic environments, soda-lime silicate, potash-lime silicate and lead silicate glasses were submerged during 300 days in synthetic marine and river solutions. The alteration was characterized through optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDS) and atomic force microscopy (AFM). The results of this induced alteration showed that the degradation mechanism is directly connected to the chemical composition of glass. In soda-lime silicate glasses the degradation proceeds in a two-step mechanism: firstly hydration and fissure development occurs, and secondly fissures grow and pits are formed. Lead silicate glass forms simultaneously pits and a recurrent alteration layer. Potash-lime silicate glasses forms stratified gel layers, which are easily detached. The potash-lime silicate glass was the least durable under aquatic conditions. Samples submerged in simulated marine water were altered faster than those submitted to river water.

In this study we evaluate the laser cleaning of tarnished pure and sterling silver substrates using a nanosecond Q-switched Nd:YAG laser at 1064, 532 and 266 nm. To assess the effects associated with cyclic laser cleaning treatments, several cycles of tarnishing followed by laser cleaning were applied on silver coupons that were characterized by gravimetry, colorimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. According to the obtained results, none of the three wavelengths is recommended for laser cleaning of pure silver objects, while for sterling silver artifacts, the visible laser wavelength of 532 nm seems the most appropriate.

This paper studies the chemical composition of the corrosion product layers formed on magnesium alloys AZ31 and AZ61 following immersion in 0.6M NaCl, with a view to better understanding their protective action. Relative differences in the chemical nature of the layers were quantified by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) and low-angle X-ray diffraction (XRD). Corrosion behavior was investigated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement. An inhibitive effect from the corrosion product layers was observed from EIS, principally in the case of AZ31, as confirmed by hydrogen evolution tests. A link was found between carbonate enrichment observed by XPS in the surface of the corrosion product layer, concomitant with the increase in the protective properties observed by EIS.

In the present study, Mg-alloy AZ31 was alloyed with low-level lutetium (Lu) additions, with the aim of generating a more protective surface oxide/film. To stimulate Lu-rich surface films, AZ31 + Lu specimens were heat treated at 400 °C for up to 300 min. Lu was not detected in the ¿-Mg matrix by EDXS; instead it was incorporated in Al¿Mn¿Lu particles. Micro-additions of Lu promoted a significant reduction of corrosion rates of as-cast AZ31, although Lu was not detected in the surface oxide as determined by XPS. The subsequent heat treatment of as-cast AZ31 + Lu had a negative impact upon corrosion.

This paper studies the differences in chemical composition of the oxide surface layers induced by heating in air at 200 °C for time intervals from 5 min up to 60 min on commercial AZ31 and AZ61 magnesium alloys with a view to a better understanding of their protective properties. A strong link was found between the aluminium enrichment observed in the surface of the oxide layer and the decrease in the protective properties of the heat treated AZ31 alloy. In contrast, no significant changes have been observed in the case of the heat treated AZ61 alloy.

This paper studies the changes in chemical composition of the thin oxide surface films induced by heating in air at 200 °C for time intervals from 5 min to 60 min on the freshly polished commercial AZ31 and AZ61 alloys with a view to better understanding their protective properties. This thermal treatment resulted in the formation of layers enriched in metallic aluminium at the interface between the outer MgO surface films and the bulk material. A strong link was found between the degree of metallic Al enrichment in the subsurface layer (from 10 to 15 at.%) observed by XPS (X-ray photoelectron spectroscopy) in the AZ61 treated samples and the increase in protective properties observed by EIS (electrochemical impedance spectroscopy) in the immersion test in 0.6 M NaCl. Heating for 5–60 min in air at 200 °C seems to be an effective, easy to perform and inexpensive method for increasing the corrosion resistance of the AZ61 alloy by approximately two or three times.

The work is an attempt to learn more about the role of several experimental variables in the corrosion of magnesium alloys in immersion tests carried out in 0.6 M NaCl. The effect of as-received and polished surface conditions, geometrical characteristics of the exposed area and different aluminium contents in the magnesium based alloys is considered. Results indicated that polished surfaces and AZ61 surfaces tend to develop corrosion slower than the respective as-received and AZ31 surfaces; these tendencies can change by prolonging exposure time. Filiform and localised corrosion are influenced by the presence of cut surfaces and small exposed areas, respectively

The influence of the processing route and chemical composition in the corrosion behaviour of two Mg-Zn-Y-Mischmetal alloys has been evaluated in phosphate buffer saline solution. The corrosion resistance of the alloy processed by conventional techniques was substantially higher than that found for the same alloy processed from atomised powders. Fine homogeneous distribution of the second-phase particles promoted severe attack due to the enhanced number of galvanic microcells. A higher concentration of zinc and a lower content of rare earth additions improved the corrosion resistance of the alloys due to the lower volume fraction of second-phase particles. © 2012 Elsevier Ltd.

[EN] The suitability of the application of Ion Beam Analysis (IBA) techniques such as Particle Induced X-ray Emission spectrometry (PIXE) and Rutherford Backscattering Spectrometry (RBS) to elemental depth profiling in concrete is analysed, studying hardened samples of concrete prior to and after a dynamic leaching test. A calibration of the data has been done by comparing the results obtained by IBA techniques with those obtained by Chemical and Thermogravimetric Analysis (TG/DTA). From PIXE and RBS data relevant information about the migration of minor elements, within the concrete matrix after leaching is obtained.

Embrittlement of high-strength steel is known to be caused by hydrogen penetration into the network of the metal. However, the penetration mechanism of hydrogen into the steel is still under discussion, as it is not so easy to detect and measure the hydrogen in steels. In this paper, relatively large commercial cold drawn pearlitic steel wires have been submitted to stress corrosion cracking under different environments. After these tests, Nuclear Resonance Reaction Analysis, NRRA, has been used to detect the presence of the hydrogen and its quantity, which has confirmed the presence of H in the case of brittle fracture. In addition, once the presence of hydrogen has been confirmed, the penetration of the hydrogen into the unit cell of the ferrite has been deduced from the analysis of the steels by neutron diffraction, from the shift of the d-spacing after the experiments. The application of NRRA and Neutron Diffraction techniques have been shown as very promising techniques to study the mechanisms of the embrittlement of the steel to the hydrogen present in the metallic lattice.

The stability of concrete in contact with water is an issue of great concern if long-term service-life is needed. High and ultra high performance concretes have been developed to enhance the durability of concretes structures, but the great differences in composition and microstructure of these concretes with regard to the traditional concrete mean that previous experience may be inapplicable. Ground water leaching resistance of high and ultra high performance concretes has been studied employing two leaching methods based on different convection regimes of the leachant: Tank Water Test (TWT) and Running Water Test (RWT). The leachability of calcium has been used to monitor leaching.

Realkalisation is an electrochemical technique for repairing concrete structures damaged by rebar corrosion due to carbonation. The treatment aims at restoring alkalinity of the concrete by application of a continuous current between the rebar, acting as a cathode, and an external auxiliary electrode placed in a carbonate solution and connected to a positive pole of a power supply. Here we report the application of neutron diffraction in the in situ monitoring of a realkalisation treatment, analysing at the same time the development of the electro-osmotic flux and the microstructural variations in the surroundings of the rebar.

Electroosmotic experiments have been carried out on eight different mixes of hardened cementitious matrixes including concrete, mortar and pastes, different types of binders, carbonated and non-carbonated specimens and different test conditions. From these trials, the zeta potential values have been determined and the optimum experimental parameters and devices have been established. In addition, the influence of the composition of the binder on the zeta potential has been quantified indicating that higher amounts of Al2O3 in the binder lead to higher positive values of zeta potential, while the SiO2 acts just on the opposite side. This has been explained in terms of the different i.e.p. (isoelectric point) for both oxides. Concerning the influence of carbonation, it increases the absolute value of the zeta potential toward more negative values; this behaviour has been attributed to the influence of the specifically adsorbed Ca2+ in the negative sites of the surface in the non-carbonated samples.

Even though the electroosmotic flux through hardened cementitious materials during laboratory realkalisation trials had been previously noticed, it has never been in-situ monitored, analysing at the same time the establishment of the electroosmotic flux and the microstructure changes in the surroundings of the rebar. In this paper, two series of cement pastes, cast with CEM I and CEM I substituted in a 35% by fly ash, previously carbonated at 100% CO2, were submitted to realkalisation treatments followed on line by simultaneous acquisition of neutron diffraction data. As a result, it has been possible to confirm the electroosmosis as the driving force of carbonates towards the rebar and to determine the range of pH in the anolyte in which most of the relevant electroosmotic phenomena takes place. On the other hand, the behaviour of the main crystalline phases involved in the process has been monitored during the treatment, with the precipitation of portlandite as main result.

The influence of an external DC voltage in an aluminous cement paste has been studied by in situ neutron diffraction, by monitoring the evolution of CaAl2O4 and Ca3Al2(OH)12 at different distances from the electrodes. The microstructure of the whole aluminous paste becomes dramatically altered. Both phases have been more attacked in zones closer to the electrodes. Major changes took place in the zone next to the positive electrode, in which the anhydrous phase has disappeared completely and the Ca3Al2(OH)12, has decreased significantly. In the cathodic zone, a decrease is also noticed due to the aluminium amphoteric character. The noticeable background diffraction increase in the area close to the positive electrode has been attributed to the formation of an amorphous alumina-like-gel that incorporated water to its composition.