Caracterización estructural y espectroscópica de fibras cristalinas de Ce0.4Zr0.6O2 crecidas mediante el método de fusión zonal asistida por láser

[EN] A structural and spectroscopic characterization of crystalline rods of Ce0.4Zr0.6O2 grown by the laser floating zone (LFZ) method is presented. A precursor rod of Ce0.4Zr0.6O2 composition was sintered at 1500 ºC in air atmosphere and then processed by the LFZ technique with a CO2 laser. The processed material was characterized by XRD, SEM and Raman spectroscopy. In the as-grown, dark-color processed rod, the Raman spectrum evolves radially from a t’-like one, corresponding to Ce0.37Zr0.63O2 composition, at the edge of the rod, to a very broad and weak, cubic-like one, at the center. The degree of cerium reduction and oxygen non-stoichiometry were determined through measurements of the electronic Raman spectrum of Ce3+. A strong Ce3+ signal was found at the core of the rod, indicating strong reduction, whereas no Ce3+ signal was detected at the edge. To restore oxygen and Ce4+ content a section of the fiber was reoxidized at 620 ºC for 24 h. A very homogeneous spectrum was found in the reoxidized sample, that was assigned to a t’-phase of composition Ce0.42Zr0.58O2.[ES] Presentamos una caracterización estructural y espectroscópica de fibras cristalinas de Ce0.4Zr0.6O2 crecidas mediante fusión zonal asistida por láser (LFZ). Una barra del material precursor, de composición Ce0.4Zr0.6O2, fue sinterizada a 1500 ºC en atmósfera de aire y después procesada por LFZ con un láser de CO2. El material procesado fue caracterizado por difracción de rayos X, microscopía electrónica de barrido y espectroscopía Raman. En la fibra recién procesada, de color gris oscuro, el espectro Raman varía radialmente desde un espectro de tipo t’, correspondiente a una composición Ce0.37Zr0.63O2, en el borde de la fibra, hasta un espectro muy ensanchado y débil, de aspecto cúbico, en el centro. El grado de reducción del cerio y la no estequiometría del oxígeno se determinaron a través de las medidas del Raman electrónico del Ce3+. La señal de Ce3+ era muy intensa en el centro de la fibra, lo que indica una fuerte reducción, mientras que no se detectó en el borde. Para restablecer el contenido de oxígeno y de Ce4+ una parte de la fibra fue reoxidada a 620 ºC durante 24 h. El espectro de la muestra reoxidada, de color amarillo pálido y muy homogénea, fue asignado a una fase t’ de composición Ce0.42Zr0.58O2.Financial support from Spanish project MAT2004-03070-C05-03 is acknowledged.Peer reviewe

Directionally solidified Al2O3-Yb3Al5O12 eutectics for selective emitters

Al2O3-Yb3Al5O12 eutectic rods were directionally solidified using the laser floating zone method at rates between 25 and 750 mm/h. The microstructure consisted of an interpenetrated network of both eutectic phases for all the growth rates. The size of the phases was strongly dependent on the growth rate, the eutectic interspacing decreasing from 4.5 µm at the lowest growth rate to 600 nm at 750 mm/h. The optical transmission of the sample with coarser microstructure was measured and compared with that of an Yb3Al5O12 single crystal grown "ad hoc" using the same method. The apparent "oscillator strength" of the single 2F7/2¿2F5/2 Yb3+ absorption band was larger in the eutectic sample than in the single crystal, which was attributed to the increase in the light path caused by multiple refractions at the eutectic interphases. The thermal emission of the eutectic rod was studied between 1000 °C and 1500 °C. An intense and relatively narrow emission band at about 1 µm corresponding to the 2F5/2¿2F7/2 Yb3+ electronic transition was observed in the whole temperature range. The intensity of the band increased with the temperature up to about 1300 °C. At higher temperatures a saturation of the selective emission was observed which was attributed to the competition between the increase in the thermal population of the excited state and the enhancement of the non-radiative de-excitation channels with the temperature

Estimación de la pérdida de producción de leche en relación con el recuento de células somáticas de leche de tanque

publishedTomo I . Sección: Sistemas Ganaderos-Economía y Gestión. Sesión: Economía II. Ponencia nº 2

Directionally solidified cobalt-doped MgO-MgAl2O4 eutectic composites for selective emitters

Cobalt-doped MgO-MgAl2O4 eutectic composites were explored for their use as selective emitters for thermophotovoltaic devices. Eutectic ceramic rods with different cobalt content were directionally solidified by using the laser floating zone technique at two processing rates to obtain microstructures with different domain sizes. Thermal emission between 1000 °C and 1500 °C and optical properties (reflectance and transmittance) at room temperature were measured in the Co-doped composites and the effect on microstructure and cobalt content was investigated. Thermal emission consisted of an intense broad band at about 1.67 µm matching with the bandgap of the InGaAs cell. The emission was ascribed to the de-excitation from the 4T1(F) multiplet to the 4A2(F) ground state of the thermally excited Co ions located in the tetrahedral sites of the MgAl2O4 phase. The selectivity of the thermal emission showed a decrease with the cobalt content due to the enhancement of other electronic transitions, which leads to keeping the cobalt content in these composites at low levels (<0.15% at Co) for their use as selective emitters

Superplastic deformation of directionally solidified nanofibrillar Al2O3-Y3Al5O12-ZrO2 eutectics

Nanofibrillar Al2O3–Y3Al5O12–ZrO2 eutectic rods were manufactured by directional solidification from the melt at high growth rates in an inert atmosphere using the laser-heated floating zone method. Under conditions of cooperative growth, the ternary eutectic presented a homogeneous microstructure, formed by bundles of single-crystal c-oriented Al2O3 and Y3Al5O12 (YAG) whiskers of ≈100 nm in width with smaller Y2O3-doped ZrO2 (YSZ) whiskers between them. Owing to the anisotropic fibrillar microstructure, Al2O3–YAG–YSZ ternary eutectics present high strength and toughness at ambient temperature while they exhibit superplastic behavior at 1600 K and above. Careful examination of the deformed samples by transmission electron microscopy did not show any evidence of dislocation activity and superplastic deformation was attributed to mass-transport by diffusion within the nanometric domains. This combination of high strength and toughness at ambient temperature together with the ability to support large deformations without failure above 1600 K is unique and shows a large potential to develop new structural materials for very high temperature structural applications

Ceramic supports with highly dense and aligned pores for moltencarbonate based CO2 separation membranes

Resumen del trabajo presentado a la XVII Conference Ceramics in Europe, celebrada en Krakow (Poland), del 10 al 14 de julio de 2022.Spanish Ministerio de Economía y Competitividad and Feder Funds grants MAT2016-77769R and BES-2017-079683; Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón through the financial support to the Research Group T02 20R.N

Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

This is a post-peer-review, pre-copyedit version of an article published in Journal of Materials Science. The final authenticated version is available online at: https://doi.org/10.1007/s10853-017-0853-8A simple phase-field model is used to address anisotropic eutectic freezing on the nanoscale in two (2D) and three dimensions (3D). Comparing parameter-free simulations with experiments, it is demonstrated that the employed model can be made quantitative for Ag-Cu. Next, we explore the effect of material properties, and the conditions of freezing on the eutectic pattern. We find that the anisotropies of kinetic coefficient and the interfacial free energies (solid-liquid and solid-solid), the crystal misorientation relative to pulling, the lateral temperature gradient, play essential roles in determining the eutectic pattern. Finally, we explore eutectic morphologies, which form when one of the solid phases are faceted, and investigate cases, in which the kinetic anisotropy for the two solid phases are drastically different

Microstructural stability and orientation relationships of directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramics up to 1600°C

Directionally Solidified Eutectics: Selected Papers from DSEC IV.Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods were directionally solidified using the laser floating zone method at different growth rates, 25, 350 and 1200mm/h. The microstructure obtained, in terms of both morphology and phase size, was strongly dependent on the growth rate. However, electron backscatter diffraction experiments showed that the growth directions were the same for all the processing rates, [0001]Al2O3//[100]EAG//[100]ZrO2. The microstructural stability was investigated up to 1600°C as a function of the growth rate. Ceramics with the largest phase size presented high stability, their microstructure remaining substantially unchanged at the highest annealing temperature for 100h. Eutectics processed at higher growth rates and with a finer microstructure showed coarsening after heat treatments. The sample grown at 350mm/h coarsened at 1450°C whereas the eutectic solidified at 1200mm/h thickened at 1400°C. The growth directions remain unaffected for all growth rates. The mechanisms of microstructural coarsening were investigated. © 2014 Elsevier Ltd.The authors acknowledge the financial support from the Ministerio de Ciencia e Innovación de España and from the FEDER funds of the European Community under project MAT2009-13979-C03-03. The authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. S. Serrano-Zabaleta thanks the Spanish Government for a grant and M.C. Mesa also thanks the Gobierno de Aragón for a grant.Peer Reviewe

The role of Ce reduction in the segregation of metastable phases in the ZrO2–CeO2 system

The complexity of the ZrO2–CeO2 phase diagram arises from several factors: the low solubility of each compound into the other one, the slow kinetics of cation diffusion, the occurrence of Ce reduction at high temperatures, and the existence of several metastable phases whose appearance and evolution depend on synthesis method and thermal history of the sample. Identification of phase content is moreover complicated because the X-ray diffractograms of some ZrO2–CeO2 phases are very close or even indistinguishable, which imposes the use of other techniques more sensitive to small oxygen displacements. In this work we present a Raman spectroscopic study of phase segregation in the ZrO2–CeO2 system between 1300 and 1650 °C, focusing on the effect of Ce reduction at high temperatures and its relation with the appearance of metastable phases upon cooling. The nature of the high-temperature defective cubic phase is discussed.This work was supported by Spanish CICYT through MAT2010-19837-C06-06 grant and Feder funds.Peer reviewe