Suchergebnisse

Las plantaciones de eucalipto (género Eucalyptus) tienen una amplia distribución a escala global y causan preocupación por los efectos que pueden ocasionar sobre el medio ambiente. En este trabajo revisamos la evolución de la superficie cubierta por los eucaliptos en Euskadi y evaluamos sus efectos ambientales a partir de la bibliografía científica existente sobre esta región y sobre la península ibérica. Entre 1986 y 2019, la superficie de plantaciones de eucaliptos se ha cuadruplicado, pasando de 4.866 a 19.643 ha, proceso este que está acelerándose a causa de la plaga de la banda marrón del pino. Los estudios publicados muestran de manera sistemática que las plantaciones de eucaliptos en Euskadi y el resto de la Península tienen un efecto medioambiental negativo si se compara con las plantaciones de pino y, especialmente, con los bosques nativos. Las plantaciones de eucalipto modifican las características del suelo y disminuyen la biodiversidad. Entre los organismos más afectados se encuentran los hongos, líquenes, plantas herbáceas, anfibios, aves e invertebrados acuáticos. También se detectan alteraciones en el funcionamiento del ecosistema, en procesos como la descomposición de hojarasca. Aunque algunas afecciones parecen ser consecuencia de la intensidad con la que se explotan estas plantaciones y podrían reducirse mediante medidas correctoras, otros efectos parecen guardar relación con las características intrínsecas del eucalipto que, en consecuencia, no pueden modificarse.Es previsible que la magnitud de los impactos se agrave conforme se incremente la superficie cubierta por eucaliptales así como el número de rotaciones en sus explotaciones.

Lamellar NiO–GDC (Gadolinium-doped Ceria) and CoO–GDC directionally solidified eutectic ceramics (DSECs) were produced by the laser floating-zone technique and subjected to reduction in order to obtain porous cermets of Ni–GDC and Co–GDC, which have potential applications as anodes in solid oxide fuel cells (SOFC). The reduction of these DSECs into porous cermets was studied at 650 °C in NiO–GDC and at 500 and 700 °C in CoO–GDC, all of them processed with similar reduction kinetics. In comparison to similar Ni–YSZ and Co–YSZ lamellar cermets previously studied, no sharp reduction front was observed. The interface between the reduced and nonreduced zones is broader, with pores homogenously distributed in wide areas. Afterwards, the microstructure, texture, and crystallography of the samples were studied by electron microscopy as well as by electron and X-ray diffraction when completely reduced. The single crystal NiO and CoO lamellae transformed into porous polycrystalline metallic lamellae. Moreover, microscopy observations revealed a porous nanostructure of Co particles obtained by reduction at low temperatures (500 °C). Many of the Co and Ni particles seemed to have roughly maintained the previous crystallographic orientation with respect to the GDC phase, although the disorder of the crystallographic orientation increased significantly. In addition, a significant amount of the Ni particles reoriented to form an epitaxial interface with the (100)–GDC surface. ; This study was funded by MAT2012-30763 and MAT2015-68078-R projects, which are financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder Program of the European Union. E.C. Dickey acknowledges support from the National Science Foundation under grant #1139792. ; Peer reviewed

The perovskite La0.15Sm0.35Sr0.08Ba0.42FeO3 − δ has been prepared by the glycine nitrate (GNC) route, varying the fuel/oxidizer ratio (glycine/nitrate, G/N = 1 and 2) and cooling rate (slow cooling and air-quenched), in order to study the influence of sample preparation on the materials' properties, in the context of their application as a cathode material for SOFCs. For this, the performance of the prepared mixed ion and electron conducting perovskite oxides is dictated by their structure, oxygen stoichiometry (3 − δ), chemical composition and thermal expansion properties. High-resolution Synchrotron X-ray powder diffraction patterns were collected at room temperature and at 700 and 800 °C. It was found that the materials had a cubic crystal structure at these temperatures. As expected, 3 − δ decreased as temperature increased, and was slightly smaller for the quenched sample. Higher electrical conductivity values were obtained for the sample with G/N = 1 (air-quenched) in the cooling rate. At 700 and 800 °C the cathode synthesized with G/N = 1 and air-quenched showed the smallest polarization resistance values in impedance spectroscopy studies. Therefore, the physicochemical and electrochemical characterization clearly demonstrated the influence of the synthetic conditions on the cathode performance. ; This research has been funded by the Ministerio de Economía, Industria y Competitividad (MAT2016-76739-R (AEI/FEDER, UE) and MAT2015-86078-R), and Departamento de Educación of the Basque Government (IT-630-13). The authors thank SGIker of UPV/EHU for technical and personnel support. This work was benefited from the BL04-MSPD beamline at ALBA. The authors thank Dr. Francois Fauth of the Experiments Division of ALBA for his assistance in situ synchrotron measurements. K. Vidal thanks UPV/EHU for funding. ; Peer reviewed

The first fluorination of the cuspidine-related phases of Ln4(Al2O7□)O2 (where Ln = Sm, Eu, Gd) is reported. A low-temperature reaction with poly(vinyl-idene difluoride) lead to the fluorine being substituted in place of oxygen and inserted into the vacant position between the dialuminate groups. X-ray photoelectron spectroscopy shows the presence of the F 1s photoelectron together with an increase in Al 2p and rare-earth 4d binding energies supporting F incorporation. Energy-dispersive X-ray spectroscopy analyses are consistent with the formula Ln4(Al2O6F2)O2, confirming that substitution of one oxygen by two fluoride atoms has been achieved. Rietveld refinements show an expansion in the cell upon fluorination and confirm that the incorporation of fluoride in the Ln4(Al2O7□)O2 structure results in changes in Al coordination from four to five. Thus, the isolated tetrahedral dialuminate Al2O7 groups are converted to chains of distorted square-based pyramids. These structural results are also discussed based on Raman spectra. ; This research was funded by the Ministerio de Economía, Industria y Competitividad (MAT2016-76739-R) (AEI/FEDER, UE), and Departamento de Educación of the Basque Government (IT-630–13). The authors thank SGIker of UPV/EHU for technical and personnel support. A. Mora´nRuiz thanks UPV/EHU for funding. ; Peer reviewed

A series of chromite perovskites with the general formula Ln1−xMxCr0.9Ni0.1O3 (Ln = La and/or Nd; M = Sr and/or Ca; x ≤ 0.25) has been prepared by three combustion synthesis routes using a different combustible substance each time: glycine, urea and sucrose. In order to isolate the effect of divalent dopant concentration from the A cation steric effects, the whole group has a fixed mean A cation radius, ≈ 1.22 Å, and cation size disorder, σ2(rA) ≈ 0.0001 Å2, but variable doping x. Their crystal structure, microstructure, electrical properties and expansion coefficients have been investigated on the basis of their possible use as anode materials for intermediate temperature solid oxide fuel cells (SOFC). Cell parameters, grain sizes, expansion coefficients and conductivities all are found to be dependent on x and the combustible substance used. The most interesting relationship is the negative dependence of the conductivity with x under H2 atmosphere: conductivity decreases with doping which is the opposite to the expected behavior for a p-type doped perovskites and has not been reported before. ; This research has been funded by the Ministerio de Economía y Competitividad (MAT2016-76739-R), the Feder program of the European Union and Dpto. Educación, Política Lingüística y Cultura of the Basque Government (IT-630-13). The authors thank for technical and human support provided by SGIker of UPV/EHU. L.Ortega-San-Martin acknowledges Departamento de Ciencias, PUCP (Peru), for funding two shorts stays at UPV/EHU. ; Peer reviewed