Functionalization of open-celled foams by homogeneous slurry based coatings
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A new technology to coat open-celled foams homogeneously by using a vertical centrifuge and shear-thinning slurries is presented. The technology is exemplified by a complex multilayer-coated foam for catalytic applications (Fig. 3). Furthermore, a new calculation model for the estimation of coating thickness and for quality assessment is introduced and proved by comparing the calculated and experimental data. Based on these results, various material combinations are shown, e.g., layers made of rough particles, zeolites, activated carbon, c-Al2O3, perovskites, mullite, and yttria–alumina–garnet on SiC–, Al2O3–, or cordierite foams. Theses “functionalized foams” can be used for a wide variety of practical applications, e.g., as adsorbents and catalysts in environmental engineering, as preforms for metal matrix composites, and for special purpose applications that require corrosion and oxidation resistance.
I. INTRODUCTION
Components made of porous ceramics or metals are well-established in the field of environmental technology, such as filtration processes at high temperatures, modern burner technologies, or solar power plants.1 For this reason, large quantities of several hundreds of millions of replica foams made by Schwartzwalder technology2 are produced per year all over the world. Nowadays, new challenges in process engineering and environmental technologies not only require cellular materials that offer functional properties like corrosion resistance, catalytic activity, or adhesion characteristics. They also require outstanding structural properties including high open porosity and network-like structures. One option to open up these new areas of application is the functionalization of ceramic foams by surface coating. In the context of catalysis, several sources refer to coatings on open-celled ceramic foams.3–5 Yet often the used coating methods are not described in detail. Moreover, most of these techniques are derived from coating dense elements and are therefore not really suitable for foam structures with their high storage properties for liquids. This results in the production of only thin and inhomogeneous coatings. However, this outcome could be improved by repeating several dip coating steps. The disadvantage of this procedure is its low efficiency. Thus, it is important to improve these coating techniques to create new strategies a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.127 2220
J. Mater. Res., Vol. 28, No. 17, Sep 14, 2013
http://journals.cambridge.org
Downloaded: 15 Mar 2015
for functionalizing sintered foam materials. This includes surface characteristics of the foam structure as well as rheological properties of the coating slurries and the coating technology itself. This work aims to present solutions for the abovementioned issues and shows the possibility of coating foam surfaces with homogeneous functional layers. The used techniques allow to build up various interesting material combinations of “foam 1 functional layer”
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