Abstract
Open-celled zinc oxide ceramic foams were prepared by the polymer sponge replication (Schwartzwalder) technique from aqueous ZnO dispersions with Sb2O3 and Bi2O3 as sintering additives, and mechanically stable ZnO foams with an average porosity of 93.6% were obtained. Their microstructure consists of ZnO grains with a Bi-containing grain boundary phase together with a Zn-Sb-O secondary phase with spinel structure. The obtained ZnO ceramic foams were characterized with respect to their morphology by computed tomography; in addition, the compressive strength and the thermal conductivity were determined, and the data were applied for modelling of the mechanical and thermal properties of the bulk ZnO strut material.
Highlights
Open-celled ceramic foams are used within several technological fields; with respect to the quantity, the most prominent applications are filter materials for metal melts in casting or catalyst supports [1]
Open-celled zinc oxide ceramic foams were prepared by the polymer sponge replication (Schwartzwalder) technique from aqueous ZnO dispersions with Sb2O3 and Bi2O3 as sintering additives, and mechanically stable ZnO foams with an average porosity of 93.6% were obtained. eir microstructure consists of ZnO grains with a Bi-containing grain boundary phase together with a Zn-Sb-O secondary phase with spinel structure. e obtained ZnO ceramic foams were characterized with respect to their morphology by computed tomography; in addition, the compressive strength and the thermal conductivity were determined, and the data were applied for modelling of the mechanical and thermal properties of the bulk ZnO strut material
Results and Discussion e dispersion of the ZnO-Sb2O3-Bi2O3 powder mixture in water using an ethanolammonium citrate-based deflocculant was successful with respect to the rheological behavior up to a solid content of 77.5 wt.%/37.9 vol.%. e obtained dispersion possessed the desired shear-thinning flow behavior and a viscosity suitable for the successful manufacturing of cellular ZnO ceramics by the polymer sponge replication technique [22, 23]
Summary
Open-celled ceramic foams are used within several technological fields; with respect to the quantity, the most prominent applications are filter materials for metal melts in casting or catalyst supports [1]. Ceramic foams for the above-mentioned applications are manufactured on an industrial scale by the polymer sponge replication process established by Schwartzwalder and Somers in 1961 [2]. Is results in a macrocellular foam-like structure similar to that of the polymeric sponge used as template in this process. To our knowledge, no zinc oxide foams have been prepared by the sponge replication process yet. Zinc oxide is a semiconductor material, which crystallizes in the wurtzite structure type in analogy to aluminum nitride or silicon carbide, for example. As a consequence of this simple structure type, the phonon conductivity is high, which results in a good thermal conductivity for adamantine compounds [6]. Pure zinc oxide has a thermal conductivity of 50 W·m−1·K−1 at room temperature, which is high for an oxidic compound [7]
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