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Scientific Papers in SCI



2021


Tribología y Protección de Superficies - Materiales Ópticos Multifuncionales

High-temperature solar-selective coatings based on Cr(Al)N. Part 1: Microstructure and optical properties of CrNy and Cr1-xAlxNy films prepared by DC/HiPIMS

Rojas, TC; Caro, A; Lozano, G.; Sanchez-Lopez, JC
Solar Energy Materials and Solar Cells, 223 (2021) 110951

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In order to explore the potentialities of Cr1-x(Al)xNy materials in multilayer-based solar selective coatings (SSC) for high temperature applications (T > 500 °C), the optical behavior of Cr1-x(Al)xNy films is studied in this work. Two sets of layers (CrNy and Cr1-xAlxNy) were prepared by direct current (DC) and high-power impulse magnetron sputtering (HiPIMS) technology. The deposition parameters: N2 flux, HiPIMS frequency and aluminum sputtering power, were modified to get a wide variety of stoichiometries. The composition, morphology, phases and electronic structure of the films were characterized in depth. The optical behavior was determined by UV–Vis–NIR and FTIR spectroscopies, and the optical constants were obtained from the measured transmittance and reflectance spectra based on appropriate dielectric function models. Our results indicate that small changes in the layer composition influence the optical constants. In particular, a metallic-like behavior was obtained for CrNy layers with N vacancies (CrN0.95 and CrN0.67 films) while a semiconductor-like behavior was observed for CrN1.08. Thus, the CrNy films can be used as effective absorber layer in multilayer-based SSC, and namely, the CrN0.67 film as an IR reflector/absorber layer too. Likewise, the optical properties of Cr1-xAlxNy layers can also be tuned from metallic to semiconductor-like behavior depending on the chemical composition. Indeed, the absorption coefficients of Cr1-xAlxNy films with optimized Al content and N-vacancies are comparable to those reported for state-of-the-art materials such as TiAlN or TiAlCrN. In addition, a Cr0.96Al0.04N0.89 film was found to be a suitable IR reflector/absorber layer.


May, 2021 | DOI: 10.1016/j.solmat.2020.110951

Reactividad de Sólidos

Synthesis and Characterization of a Nearly Single Bulk Ti2AlN MAX Phase Obtained from Ti/AlN Powder Mixture through Spark Plasma Sintering

Salvo, C; Chicardi, E; Poyato, R; Garcia-Garrido, C; Jimenez, JA; Lopez-Pernia, C; Tobosque, P; Mangalaraja, RV
Materials, 14 (2021) 2217

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MAX phases are an advanced class of ceramics based on ternary carbides or nitrides that combine some of the ceramic and metallic properties, which make them potential candidate materials for many engineering applications under severe conditions. The present work reports the successful synthesis of nearly single bulk Ti2AlN MAX phase (>98% purity) through solid-state reaction and from a Ti and AlN powder mixture in a molar ratio of 2:1 as starting materials. The mixture of Ti and AlN powders was subjected to reactive spark plasma sintering (SPS) under 30 MPa at 1200 degrees C and 1300 degrees C for 10 min in a vacuum atmosphere. It was found that the massive formation of Al2O3 particles at the grain boundaries during sintering inhibits the development of the Ti2AlN MAX phase in the outer zone of the samples. The effect of sintering temperature on the microstructure and mechanical properties of the Ti2AlN MAX phase was investigated and discussed.


May, 2021 | DOI: 10.3390/ma14092217

Química de Superficies y Catálisis

Effect of the sulphonating agent on the catalytic behavior of activated carbons in the dehydration reaction of fructose in DMSO

Bounoukta, CE; Megias-Sayago, C; Ivanova, S; Penkova, A; Ammari, F; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 617 (2021) 118108

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A series of -SO3R functionalized activated carbons (R=H, O, aryl) were prepared and applied in fructose dehydration reaction to 5-hydroxymethylfurfural. Different sulphonating methods introduce groups on catalyst surface with distinct donor-acceptor and hydrophilic properties. Their nature influences significantly not only activated carbon?s textural and chemical properties but also the product yields and selectivity in fructose dehydration reaction. The viability of the solvent free reaction was also investigated and compared to the performance of the catalyst series in presence of DMSO, where the best catalytic results were obtained.


May, 2021 | DOI: 10.1016/j.apcata.2021.118108

Materiales Avanzados

Effects of an Illite Clay Substitution on Geopolymer Synthesis as an Alternative to Metakaolin

Eliche-Quesada, D; Bonet-Martinez, E; Perez-Villarejo, L; Castro, E; Sanchez-Soto, PJ
Journal of Materials in Civil Engineering, 33 (2021) 04021072

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In this study, a calcined illite clay from Bailen, Jaen, Spain, was valorized as a substitute of metakaolin in the synthesis of new geopolymeric materials. The raw materials, raw clay and commercial kaolin, were pretreated at 750 degrees C (4 h). Several samples (0%-100% by weight of clay) were activated by mixing NaOH solution and sodium silicate solution. The specimens were cured (60 degrees C and 99% relative humidity) for 24 h, then demolded and kept at ambient conditions for 7, 28, and 90 days. The prepared geopolymers were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Physical, mechanical, and thermal properties were determined. The results indicated that the specimens based on the illite raw clay and metakaolin present an amorphous consolidated appearance, characteristic of the polycondensation reactions. The incorporation of up to 50% by weight of raw clay provided geopolymers with higher mechanical strength (39.6 MPa) and bulk density (1,455 kg/m(3)), lower apparent porosity (19.6%), and similar although slightly higher thermal conductivity (0.25 W/mK) than control geopolymers containing only metakaolin as a precursor after 28 days of curing. Control geopolymers presented compressive strength, bulk density, apparent porosity, and thermal conductivity of 23 MPa, 1,251 kg/m(3), 41.03% and 0.224 W/mk, respectively, at the same age of cured geopolymers. The mechanical properties increased with curing time due to a greater advance of the geopolymerization reaction. Therefore, this illite clay can be thermally activated together with metakaolin to obtain geopolymers with suitable technological properties. The results demonstrate that the finished materials can be used for construction applications.


May, 2021 | DOI: 10.1061/(ASCE)MT.1943-5533.0003690

Química de Superficies y Catálisis

IR spectroscopic insights into the coking-resistance effect of potassium on nickel-based catalyst during dry reforming of methane

Azancot, L; Bobadilla, LF; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 285 (2021) 119822

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Dry reforming of methane (DRM) is an effective catalytic route for transforming CO2 and CH4 into valuable syngas and thus potentially attractive for mitigating the emission of environmental harmful gases. Therefore, it is crucial to develop rationally Ni-based catalysts highly resistant to coking and sintering. In this scenario, the addition of small amounts of potassium to nickel catalyst increases their resistance to coking during dry reforming of methane. Nonetheless, the specific role of potassium in these catalysts not have been fully understood and there are still important discrepancies between the different reported studies. This work provides a new approach on the anticoking nature of a K-promoted Ni catalyst by means of a combined IR spectroscopic study of in situ characterization by CO adsorption under static conditions and operando DRIFTS measurements under dynamic conditions of DRM reaction. The involved surface species formed during the reaction were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that the existence of Ni-K interfacial sites favours the gasification of carbonaceous deposits towards reverse Boudouard reaction and reduces the sticking probability of CO2 dissociative adsorption. Moreover, the presence of strongly Mg-O-K basic sites leads to the formation of carbonate intermediates that are subsequently reduced into CO gaseous towards the associative mechanism by RWGS reaction. These results provide a fundamental understanding of the relevant anticoking effect of potassium on Ni-based catalysts.


May, 2021 | DOI: 10.1016/j.apcatb.2020.119822

 

 

 

 

 

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