Scientific Papers in SCI


Title: Influence of the synthesis parameter on the interlayer and framework structure of lamellar octadecyltrimethylammonium kanemite
Author(s): Corredor, JI; Cota, A; Pavon, E; Osuna, FJ; Alba, MD
Source: Applied Clay Science, 95 (2014) 9-17

abstract | fulltext

Inorganic–organic nanostructures, used as host materials for selective adsorption of functional molecules and as mesostructured material precursors, can be constructed by the interlayer modification of inorganic layered materials with surfactants. The formation mechanism is mainly determined by the surfactant assemblies in the 2D limited space. In this paper, a detailed structural analysis of the lamellar mesophases prepared from kanemite, a lamellar silicate, and octadecyltrimethylammonium (ODTMA) under various conditions was reported. The adsorbed amount of ODTMA and the long and short range structural orders were explored by TGA, XRD, IR/FT and MAS NMR spectroscopies. The results revealed that ODTMA molecules were efficiently intercalated in the interlayer space of kanemite and, in all synthesis conditions, an ordered lamellar structure was obtained. The ODTMA adsorption in kanemite caused changes not only in the interlayer space but also in the silicate framework, where five-member rings were formed. The characteristics of the final products were influenced by the synthesis conditions, although the separation mode, filtration or centrifugation, was not relevant. Therefore, the adsorption conditions of ODTMA in kanemite will contribute to the design of novel layered materials with potential environmental and technological use.

June, 2014 | DOI: 10.1016/j.clay.2014.02.030

Title: Quantification and comparison of the reaction properties of FEBEX and MX-80 clays with saponite: Europium immobilisers under subcritical conditions
Author(s): Villa-Alfageme, M; Hurtado, S; Castro, MA; El Mrabet, S; Orta, MM; Pazos, MC; Alba, MD
Source: Applied Clay Science, 101 (2014) 10-15

abstract | fulltext

The evaluation of the retention mechanisms in FEBEX and MX-80 bentonites, selected as reference materials to construct engineered barriers, carries major implications in the safe storage of immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with Eu(NO3)3 (151Eu and 153Eu, with 52.2% 153Eu) and spiked with radioactive 152Eu for the quantification of the reactions. Results were compared with saponite as the reference smectite. The strong dependence of the reaction parameters with temperature and time was quantified and the reaction velocity was evaluated. The velocity follows these trends: 240 days are needed for the total retention of europium for temperatures over 200 °C; below 150 °C, significantly longer reaction times, on the order of three years, are required to complete the reaction. Clays do not influence velocity rates, but the retention capacity of bentonites remains lower than for saponite. At 300 °C, the milliequivalents retained by the three clays are consistently over CEC. The structural analyses reveal not only adsorption of europium but also the presence of Eu(OH)3 precipitation and Eu2SiO3 confirming the existence of a chemical reaction.

November, 2014 | DOI: 10.1016/j.clay.2014.08.012

Title: c- C4F8 Plasmas for the Deposition of Fluorinated Carbon Films
Author(s): Terriza, A; Macias-Montero, M; Lopez-Santos, MC; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Source: Plasma Processes and Polymers, 11 (2014) 289-299

abstract | fulltext

Highly fluorinated polymeric (CFX), fluorine containing diamond-like carbon (F-DLC) and, for comparison, diamond-like carbon (DLC) films have been plasma deposited in a RF parallel plate reactor by using c-C4F8 as fluorine precursor and different mixtures of argon, C2H2, and H2. Plasmas have been characterized by optical emission spectroscopy, mass spectrometry, and Langmuir probe measurements. Differences in the film composition and structure have been related with the type of species formed in the plasma and with the self-bias potential developed at the deposition electrode. Additional experiments using CF4 have confirmed that the formation in the plasmas of neutral or ionized CxFy species with x > 2 is a critical factor for the synthesis of fluorine rich films.

March, 2014 | DOI: 10.1002/ppap.201300129

Title: On the Deposition Rates of Magnetron Sputtered Thin Films at Oblique Angles
Author(s): Alvarez, R; Garcia-Martin, JM; Lopez-Santos, MC; Rico, V; Ferrer, FJ; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Source: Plasma Processes and Polymers, 11 (2014) 571-576

abstract | fulltext

We describe here the deposition of thin films using magnetron sputtering at oblique angles. General relations between the deposition rates of the films and experimental parameters, such as gas pressure or substrate tilt angles, are deduced and experimentally tested. The model also permits the direct determination of the thermalization mean free path of the sputtered particles in the plasma gas, a key parameter defining the balance between ballistic and diffusive flows in the deposition reactor. The good agreement between experimental and calculated results supports the validity of our description, which becomes a useful tool to explain the main features of the magnetron sputtering deposition of thin films at oblique angles.

June, 2014 | DOI: 10.1002/ppap.201300201

Title: Plasma Deposition of Superhydrophobic Ag@ TiO2 Core@ shell Nanorods on Processable Substrates
Author(s): Macias-Montero, M; Borras, A; Romero-Gomez, P; Cotrino, J; Frutos, F; Gonzalez-Elipe, AR
Source: Plasma Process and Polymers, 11 (2014) 164-174

abstract | fulltext

This work reports the low temperature plasma formation of Ag@TiO2 nanorods (NRs) on processable substrates. The layers have been analyzed by electron microscopy and secondary ion mass spectroscopy. The NRs morphologies suggest that the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining their shape, dimensions, and tilting orientation. Both amorphous and anatase Ag@TiO2 NRs surfaces are superhydrophobic, and turn into superhydrophilic by irradiation with UV light. This wetting behavior is discussed by considering the water penetration in the inter-NR space during the light-mediated transformation.

February, 2014 | DOI: 10.1002/ppap.201300112

Title: Phase assembly and electrical conductivity of spark plasma sintered CeO2-ZrO2 ceramics
Author(s): Poyato, R; Cruz, SA; Cumbrera, FL; Moreno, B; Chinarro, E; Odriozola, JA
Source: Journal of Materials Science, 49 (2014) 6353-6362

abstract | fulltext

Cex Zr1−x O2 (x = 0.10, 0.16 and 0.33) nanocrystalline powders were obtained by a two-step synthesis technique and sintered by spark plasma sintering (SPS). As consequence of the reduction of Ce4+ to Ce3+ species by carbon in the graphite environment in SPS, phase assemblies including tetragonal, monoclinic and pyrochlore phases were generated in the ceramics during the sintering process. The electrical conductivity was highly dependent on phase assembly and atmosphere (N2, H2 and O2). A significant decrease in the activation energy was noticed in the ceramics with high pyrochlore content when measuring the conductivity in H2 atmosphere, consequence of the strong reduction promoted in these ceramics during the measurement. Equal conduction behavior with similar activation energy was observed in all the ceramics when measuring in O2 atmosphere.

June, 2014 | DOI: 10.1007/s10853-014-8361-6

Title: Hardness and flexural strength of single-walled carbon nanotube/alumina composites
Author(s): Gallardo-Lopez, A; Poyato, R; Morales-Rodriguez, A; Fernandez-Serrano, A; Munoz, A; Dominguez-Rodriguez, A
Source: Journal of Materials Science, 20 (2014) 7116-7123

abstract | fulltext

This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol% single-walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al2O3 and composites were spark plasma sintered (SPS) in identical conditions at 1300 A degrees C, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNT along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three-point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicates that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical properties of these composites, they are not the main cause for the reported decay in flexural strength.

October, 2014 | DOI: 10.1007/s10853-014-8419-5

Title: Characterization of porous graphitic monoliths from pyrolyzed wood
Author(s): Gutierrez-Pardo, A; Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J
Source: Journal of Materials Science, 49 (2014) 7688-7696

abstract | fulltext

Porous graphitic carbons were obtained from wood precursors using Ni as a graphitization catalyst during pyrolysis. The structure of the resulting material retains that of the original wood precursors with highly aligned, hierarchical porosity. Thermal characterization was performed by means of thermogravimetry and differential scanning calorimetry, and the onset temperature for graphitization was determined to be similar to 900 A degrees C. Structural and microstructural characterization was performed by means of electron microscopy, electron and x-ray diffraction, and Raman spectroscopy. The effect of maximum pyrolysis temperature on the degree of graphitization was assessed. No significant temperature effect was detected by means of Raman scattering in the range of 1000-1400 A degrees C, but at temperatures over the melting point of the catalyst, the formation of graphite grains with long-range order was detected.

November, 2014 | DOI: 0.1007/s10853-014-8477-8

Title: Wall paintings studied using Raman spectroscopy: A comparative study between various assays of cross sections and external layers
Author(s): Perez-Rodriguez, JL; Robador, MD; Centeno, MA; Siguenza, B; Duran, A
Source: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 120 (2014) 602-609

abstract | fulltext

This work describes a comparative study between in situ applications of portable Raman spectroscopy and direct laboratory measurements using micro-Raman spectroscopy on the surface of small samples and of cross sections. The study was performed using wall paintings from different sites of the Alcazar of Seville.

Little information was obtained using a portable Raman spectrometer due to the presence of an acrylic polymer, calcium oxalate, calcite and gypsum that was formed or deposited on the surface. The pigments responsible for different colours, except cinnabar, were not detected by the micro-Raman spectroscopy study of the surface of small samples taken from the wall paintings due to the presence of surface contaminants.

The pigments and plaster were characterised using cross sections. The black colour consisted of carbon black. The red layers were formed by cinnabar and white lead or by iron oxides. The green and white colours were composed of green emerald or atacamite and calcite, respectively. Pb3O4 has also been characterised. The white layers (plaster) located under the colour layers consisted of calcite, quartz and feldspars. The fresco technique was used to create the wall paintings.

A wall painting located on a gypsum layer was also studied. The Naples yellow in this wall painting was not characterised due to the presence of glue and oils.

This study showed the advantage of studying cross sections to completely characterise the pigments and plaster in the studied wall paintings.

February, 2014 | DOI: 10.1016/j.saa.2013.10.052

Title: Self-propagating combustion synthesis via an MSR process: An efficient and simple method to prepare (Ti, Zr, Hf)B2–Al2O3 powder nanocomposites
Author(s): Sayagues, MJ; Aviles, MA; Cordoba, JM; Gotor, FJ
Source: Powder Technology, 256 (2014) 244-250

abstract | fulltext

The synthesis of (Ti1 − xZrx)B2–Al2O3, (Ti1 − xHfx)B2–Al2O3 and (Zr1 − xHfx)B2–Al2O3 (x = 0, 0.5 and 1) powder nanocomposites via a mechanochemical method using TiO2, ZrO2, HfO2, HBO2 and Al as the raw materials was investigated. The formation of the nanocomposites proceeds via a mechanically-induced self-sustaining reaction (MSR) process that involves several simultaneous reactions. The aluminothermic reductions of the TMO2 and HBO2 produce Al2O3 and transition metal and boron elements, which in turn react to yield the diboride phase. The ignition of the complex combustion reaction occurred after a short milling time (15–30 min), instantly transforming most of the reactants into products. The sample composition was marked by the stoichiometry of the combustion reaction, and the resulting nanocomposites were analysed using XRD, ED, SEM, TEM and EDX techniques. The X-ray results confirmed the biphasic character of the prepared composite powder (TMB2 and Al2O3 structures); minor amounts of the Zr and Hf oxides were also observed. The achieved microstructure was characterised by the agglomeration of Al2O3 nanocrystallites and diboride crystals with a diffraction domain size ranging between 100 and 300 nm.

April, 2014 | DOI: 10.1016/j.powtec.2014.02.031

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