Artículos SCI

Abstract

The present article focuses on an interdisciplinary research on cultural heritage concerning the microanalysis of Gothic mural paintings made during the 15th century in Slovenia. The samples were chosen from the churches of Crngrob (1453), Mirna (1463-1465), Mevkuz (1465) and Mate (1467), attributed to two of the most important Gothic painters of that period of time: Master Bolfgang and Master of Mate. The chemical and phase composition of all the mortars, number of their layers and selection of the pigments were of interest. For this purpose, fragments of mural paintings were studied with several instrumental techniques: optical microscopy (OM), SEM-EDX, x-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In early artworks, the mortar was made using a mixture of lime and more or less clean sand. Later, crushed lime-rock or marble instead of sand was added to lime. The pigments identified by EDX microanalysis of cross sections previously studied by OM, are of earth or mineral origin. Therefore, they are durable in fresco and lime techniques: lime white, yellow and red natural or burned ochres, green earth and azurite. The results confirmed the high technical quality of both painters and the relationships between the teacher and the disciple. Master Bolfgang and Master of Mate combine three basic techniques of mural painting: fresco, secco and lime techniques. This kind of investigation and methodology allow us to know better the Central European Art and the Slovenian Art in the Adriatic zone, as well as the general map of European Art in the 14-15th centuries.

Julio, 2008 · DOI: 10.1002/xrs.1050

Abstract

A series of Au/TiO2 samples with gold loadings ranging from 0.11% to 1.26% have been prepared by deposition-precipitation, characterised by means of XRD, S-BET, XRF, TEM, XPS and DR UV-Vis techniques and tested in the gaseous CO oxidation and photocatalytic degradation of phenol in aqueous media. The catalytic performances of the solids on both reactions depend on the gold content. Besides this, the gold particle size plays a determinant role in the catalytic activity for the CO reaction, but apparently its influence on the photocatalytic activity appears to be negligible and only very small gold particles seem to participate on the photocatalytic process. On the other hand, the electronic properties of the solids, measured by its band gap energy, are a key factor in the photochemical activity but do not have a clear influence in the CO oxidation reaction.

Julio, 2008 · DOI: 10.1007/s10562-008-9448-y

Abstract

The crystal growth kinetics of antimony trisulfide in (GeS2)(0.1)(Sb2S3)(0.9) glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 <= T <= 515 K (E-G = 405 +/- 7 kJ mol(-1)). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.equation. 

Junio, 2008 · DOI: 10.1016/j.jnoncrysol.2008.01.029

Abstract

This work is devoted to the investigation of decorative zirconium oxynitride, ZrOxNy, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about 9 SCCM (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to 12 SCCM). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and 14 SCCM). The films deposited with gas flows above 14 SCCM showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in the film structure and electronic properties, thus opening new potential applications for the films, beyond those of purely decorative ones. Taking this into account, the electrical behavior of the films was investigated as a function of the reactive gas flow and correlated with the observed chemical, electronic, and structural features. The variations in composition disclosed the existence of four different zones, which were correlated to different crystalline structures. For the so-called zone I, x-ray diffraction revealed the development of films with a B1 NaCl face-centered cubic zirconium nitride-type phase, with some texture changes. Increasing the reactive gas flow, the structure of the films is that of a poorly crystallized overstoichiometric nitride phase, which may be similar to that of Zr3N4, but with some probable oxygen inclusions within nitrogen positions. This region was characterized as zone II. Zone III was indexed as an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions. Finally, occurring at the highest flow rates, zone IV was assigned to a ZrO2 monoclinic-type structure. The composition/structure variations were consistent with the chemical bonding analysis carried out by x-ray photoelectron spectroscopy, which showed oxygen doping in both Zr3N4- and ZrN-type grown films. The electronic properties of the films exhibited significant changes from zone to zone. Resistivity measurements revealed a very wide range of values, varying from relatively highly conductive materials (for zone I) with resistivity values around few hundreds of mu Omega cm to highly insulating films within zones III and IV, which presented resistivity values in the order of 10(15) mu Omega cm. Regarding zone II, corresponding to oxygen doped Zr3N4-type compounds, the observed behavior revealed resistivity values increasing steeply from about 10(3) up to 10(15) mu Omega cm, indicating a systematic transition from metallic to insulating regimes. 

Mayo, 2008 · DOI: 10.1063/1.2927494

Abstract

An important improvement of the photocatalytic activity of sol-gel prepared TiO2 has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.
The presence of sulphuric acid clearly stabilised TiO2 surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO2 surface was studied.
Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO2. Simultaneously sulphated and platinised TiO2 samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO2 Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.
A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.

Mayo, 2008 · DOI: 10.1016/j.apcatb.2007.11.036

Abstract

The effect of ultrasound in the modification of a Colombian bentonite pillared with mixed solutions of Al-Ce and Al-Ce-Fe was obtained. The solids were characterized by means of X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. The catalysts were very efficient in the phenol oxidation reaction in diluted aqueous medium under mild experimental conditions (298 K and atmospheric pressure) and in the CO oxidation reaction. The use of ultrasound showed a clear effect in the synthesis of this type of solids allowing to make their synthesis in a shorter period of time and conserving the physical-chemical characteristics as well as catalytic activity in the oxidation reactions. 

Abril, 2008 · DOI: 10.1016/j.cattod.2007.12.129

Abstract

Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA), DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks and annealing of microstructure irregularities of the talc samples on heating in the range 200-500 degrees C.

For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized as a decrease of radon mobility in the range 785-825 degrees C and by a DTA exothermal effect with the maximum at 830 degrees C. ETA results characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental data measured during heating to 600 and 1300 degrees C, respectively, and subsequent cooling to room temperature.

Abril, 2008 · DOI: 10.1007/s10973-007-8819-8

Abstract

Surface plasmon resonance measurements and magnetic characterization studies have been carried out for two types of thiol-capped gold nanoparticles (NPs) with similar diameters between 2.0 and 2.5 nm and different organic molecules linked to the sulfur atom: dodecanethiol and tiopronin. In addition, Au NPs capped with tetraoctyl ammonium bromide have also been included in the investigation since such capping molecules weakly interact with the gold surface atoms and, therefore, this system can be used as a model for naked gold NPs; such particles presented a bimodal size distribution with diameters around 1.5 and 5 nm. The plasmon resonance is non-existent for tiopronin-capped NPs, whereas a trace of such a feature is observed for NPs covered with dodecanethiol molecules and a bulk-like feature is measured for NPs capped with tetralkyl ammonium salts. These differences would indicate that the modification of the surface electronic structure of the Au NPs depends on the geometry and self-assembling capabilities of the capping molecules and on the electric charge transferred between Au and S atoms. Regarding the magnetization, dodecanethiol-capped NPs have a ferromagnetic-like behaviour, while the NPs capped with tiopronin exhibit a paramagnetic behaviour and tetralkyl ammonium-protected NPs are diamagnetic across the studied temperature range; straight chains with a well-defined symmetry axis can induce orbital momentum on surface electrons close to the binding atoms. The orbital momentum not only contributes to the magnetization but also to the local anisotropy, giving rise to permanent magnetism. Due to the domain structure of the adsorbed molecules, orbital momentum is not induced for tiopronin-capped NPs and the charge transfer only induces a paramagnetic spin component.

Abril, 2008 · DOI: 10.1088/0957-4484/19/17/175701

Abstract

The causes and degree of alteration of metals such as gold, tin, silver and bronze powders from ornamental implements of Andalusia Cultural Heritage have been studied. The unaltered gold is lost due to the alteration of the material used to adhere the leaf gold on the ceramic. Tin is transformed to romarchite and is lost due to a similar alteration as with the gold leaf adhesive. Silver is altered to Ag2S due to environmental contamination. Part of the bronze powders and silver used in Huercal-Overa altarpiece are altered to atacamite and AgCl, respectively, due to an unsuitable cleaning process.

Abril, 2008 · DOI: 10.1016/j.culher.2007.10.005

Abstract

A theoretical analysis of the influence of mass-transfer effect on the kinetic of solid-gas reactions has been carried out by assuming that the partial pressures of the gases generated in the reaction are proportional to the reaction rate. The influence of mass-transfer phenomena on the apparent activation energy, calculated by the isoconversional methods of Friedman, and on the reaction model is discussed. In the present study, simulated nonisotherm, isotherm, and controlled rate thermal analysis (CRTA) data have been used. Master plots based on the differential forms of the kinetic equations describing solid-state reactions have been employed by using the concept of the generalized time (theta), introduced by Ozawa; this permits the application of these master plots to the kinetic analysis of reactions whatever the type of temperature program used for recording the experimental data. it has been shown that when the simulated mass-transfer effect is present the variable effective activation energy E remains nearly constant while the reaction model approaches zero order.

Abril, 2008 · DOI: 10.1002/kin.20308

Abstract

In this report we investigate the structure-activity relationship in Ti-M (M = V, Mo, Nb, W) mixed-metal oxides with anatase structure used for the photoelimination of toluene under sunlight-type excitation. These systems were prepared by a microemulsion method, and their physicochemical properties were characterized by a multitechnique approach using X-ray diffraction-Rietveld, photoelectron spectroscopy, and Raman and UV-visible spectroscopy. The preparation method allowed the incorporation of up to around 20 at % of Mo, Nb, and W, whereas a significantly inferior solubility limit, below 5 at % was observed for V. The presence of nonpunctual defects, intimately related to the existence of MOx clustering, produced electronic mid-gap states involved in charge recombination and appeared to be the most negative factor influencing photoactivity. The maximization of photoactivity occurred for Ti-M samples with the highest doing level, together with a minimum structural disturbance of the anatase-type structure. The physicochemical bases for the photoactivity behavior of the Ti-M samples as function of the M content and, in particular, the presence of partial (for a specific Ti-M series) or global maxima are discussed. 

Marzo, 2008 · DOI: 10.1016/j.jcat.2008.01.005

Abstract

The vapor sorption properties of multilayers made of ordered mesoporous thin films with tailored composition and mesostructure are herein investigated. Optical reflectance measurements versus partial pressure of several vapors are performed to analyze the interplay between the affinity to and the accessibility of the different types of layers in the structure. We find that the behavior of a mesoporous oxide layer within the multilayer largely differs from that of the isolated thin film, its sorption properties being determined by the interaction with neighboring films. An explanation of the phenomena observed in these complex systems is provided in terms of the pore size, the affinity of each type of layer to specific compounds, and the effect of neighboring layers in the sorption properties of bilayers by an independent environmental ellipsometric study.

Marzo, 2008 · DOI: 10.1021/jp710612y

Abstract

Herein we establish a clear relation between the parameters that govern the growth dynamics and the structural quality of colloidal crystal films. We report an optical analysis of the spatial distribution of intrinsic defects in colloidal crystal films and correlate our results with a theoretical model describing the growth dynamics of such lattices. We find that the amount of defects fluctuates periodically and decreases along the growth direction of the lattice. We demonstrate that these spatial variations are a direct consequence of the temporal oscillations of the crystal film formation velocity, which are inherent to the colloidal particle deposition process.

Marzo, 2008 · DOI: 10.1063/1.2883943

Abstract

We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substrates, namely, SiO2, Al2O3, and MgO. The main line of the Ni 2p spectra is attributed to the bulk component, and the shoulder at 1.5 eV higher binding energies to the surface component. The spectra of the NiO thin films show strong differences with respect to that of bulk NiO. The energy separation between the main peak and the shoulder increases with the substrate covalence. This indicates the strong covalent interactions between the NiO thin films and the oxide substrates, and reflects changes in the bonding at the interface from a more ionic to a more covalent interaction. These conclusions are supported by cluster model calculations with a reduced O 2p-Ni 3d hybridization.

Febrero, 2008 · DOI: 10.1103/PhysRevB.77.075411

Abstract

In spite of the diamagnetic behavior exhibited by bulk ZnO and Au, a ferromagnetic-like behavior is induced in nanoparticles of both systems by appropriate surface functionalization. By capping with thiol derivatized molecules, magnetic hysteresis is observed even at room temperature, whereas the magnetization has a very little temperature dependence. Capping induces an alteration of their electronic configuration that depends on the capping molecule, as evidenced by X-ray absorption spectroscopy, that strongly affects their magnetic properties.

Enero, 2008 · DOI: 10.12693/APhysPolA.113.515

Abstract

The transition metal nitride ternary show similar properties to the binary nitride and some times this behaviour are improved. In the present work, the molybdenum-iron nitride has been prepared by reactive grinding from the two metals under nitrogen atmosphere at a pressure of 11 bar. The characterization of the compound is presented and it is also shown a study of the stability of the nitride under several atmospheres.

Enero, 2008 · DOI:

Abstract

A titanium foil has been subjected to laser irradiation "in situ" in a pre-chamber of an X-ray photoemission spectrometer under different atmospheres (vacuum, Ar, 02, air, N-2 and H-2). As a result of these treatments, a high amount of the carbon contamination layer was removed and other changes in composition were induced. Nitridation was achieved by laser irradiation under nitrogen. The most effective treatment protocol included an initial cleaning procedure induced by irradiation in vacuum, followed by a second irradiation process performed under nitrogen. Partial nitridation is also observed when irradiating under synthetic air. Lateral and depth analysis of the nitrogen concentration around the laser spot has been also carried out. It is found that the outermost layers present a similar concentration of nitrogen. In addition, the measured nitrogen profile indicates that the amount of nitrogen within the laser spot region is relatively lower than within the immediately surrounding area. Almost no nitrogen remains in the spot area after sputtering for 30 min. A model is proposed to account for the observed titanium surface nitridation processes.

Enero, 2008 · DOI: 10.1016/j.surfcoat.2007.06.061

Abstract

Sample controlled reaction temperature (SCRT) has been used for the first time to study the kinetics of the carbothermal reduction of silica in nitrogen to obtain silicon nitride (Si3N4). It is noteworthy to point out that SCRT method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperature gradients at a negligible level to avoid any heat or mass transfer phenomena. It has been shown that the carbothermal synthesis of silicon nitride is best described by a two-dimensional diffusion kinetic model with an activation energy of about 306 kJ/mol. Effects of experimental parameters on the activation energy has been investigated. By using SCRT it has been possible to obtain ceramic powder with a determined phase composition and a controlled microstructure. 

Enero, 2008 · DOI: 10.1016/j.jmatprotec.2007.05.004

Abstract

A full characterization of amorphous or nanostructured coatings at the microstructural level has some intrinsic difficulties associated with the lack of long range order and reference compounds, which often make difficult their study. Only by the combination of different characterization techniques is possible in many cases to achieve valuable chemical and structural information. In this paper, three different systems were used to illustrate how the combination of characterization techniques, as TEM associated to ED or EELS, EFTEM, SEM, XPS, RBS and XRD was determinant to correlate microstructure with deposition parameters and properties in such complex systems. The coatings were deposited on silicon and AISI M2 steel substrates by magnetron sputtering under different Ar/N-2 gas mixtures from Ti and C targets (system 1 and 2) or a Si target (system 3). In each case, the performed characterization allowed to get a deeper understanding of the whole system and explain their mechanical response. The studied systems are: (i) Ti-TiN-CNx multilayered coatings: the chemical and structural analysis shows that a gradual enrichment in nitrogen and nitride phases from the metallic substrate to the CNx top layer is responsible for the improvement of the adhesion properties. (ii) Ti-C-N: the existence of a nanocrystalline TiC phase embedded in an amorphous carbon matrix is demonstrated by the microstructural and chemical analysis for samples prepared under pure Ar. When N-2 is introduced in the gas phase, the nanocrystalline structure is not seen and the chemical composition is enriched in amorphous non-stoichiometric CNx. (iii) SiOxNy: although the coatings present similar composition, small differences in microstructure are observed, which can be responsible for different mechanical properties.

Septiembre, 2008 · DOI: 10.1051/epjap:2008114