Abstract
Open-celled ceramic composite foams were prepared from NiO and yttria-stabilized zirconia (YSZ) powders by the polymer sponge replication (Schwartzwalder) technique using the respective aqueous dispersions. Mechanically stable NiO–YSZ foams with an average porosity of 93 vol.% were obtained. After chemical reduction of the NiO phase with hydrogen, cellular Ni–YSZ cermet structures were obtained. They are characterized by an electric conductivity up to 19∙103 S∙m−1 which can be adjusted by both, the Ni volume fraction, and the sintering/reduction procedure. The NiO–YSZ ceramic foams, as well as the cellular Ni–YSZ cermets prepared therefrom, were characterized with respect to their microstructure by scanning electron microscopy, confocal Raman microscopy and X-ray diffraction with Rietveld analysis. In addition, the compressive strength, the electric conductivity and the thermal conductivity were determined. The collected data were then correlated to the sample microstructure and porosity and were also applied for modelling of the mechanical and electric properties of the bulk Ni–YSZ strut material.
Highlights
Cellular structures are described for all of the material classes: metals, ceramics/glasses and polymers [1,2]
For all NiO–yttria-stabilized zirconia (YSZ) dispersions prepared, the flow behavior was sufficient for the manufacturing of cellular ceramics following the Schwartzwalder process
The obtained foams are characterized by a high strut porosity, which limits the mechanical strength to low values around 0.15 MPa
Summary
Cellular structures are described for all of the material classes: metals, ceramics/glasses and polymers [1,2]. Cellular composites consisting of an interpenetrating phase network within the strut material are seldom described. Some examples are silicon carbide ceramic foams strut-infiltrated with liquid silicon (SiSiC foams, reference [5]), or oxide-bonded SiC foams functionalized with a metal phase by a salt infiltration and subsequent chemical reduction (MESCAL process, reference [6]). The resulting composite foams possess new functionalities—for example electric conductivity for the cellular metal@SiC structures or a good thermal stability for the SiSiC foams. Due to the separation of manufacturing the cellular structure from the following functionalization, the preparative effort is very high. A different approach has been investigated within this study, which is well-known for the manufacturing of bulk ceramic–metal composites (cermets).
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