Microstructure, texture, and crystallography in Ni–GDC and Co–GDC porous cermets obtained from directionally solidified eutectic ceramics
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. S. Serrano-Zabaleta would like to thank Dr. J. Liu, Dr. E. Mily, Dr. A. Moballegh, Dr. W. Cheng, Dr. M. Burch, D. Oni, E. Grimley, D. Monroe, and H. Dycus from the NCSU for all the support and help provided. The use of Servicio General de Apoyo a la Investigación (SAI, University of Zaragoza) is additionally acknowledged. The authors acknowledge the use of the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the U.S. National Science Foundation.
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Conflict of interest
The authors state that there is no conflict of interest that could potentially influence or bias the submitted work.
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