Functionalization of open-celled foams by homogeneous slurry based coatings

Abstract

A new technol. to coat open-celled foams homogeneously by using a vertical centrifuge and shear-thinning slurries is presented. The technol. is exemplified by a complex multilayer-coated foam for catalytic applications (Fig. 3). Furthermore, a new calcn. model for the estn. of coating thickness and for quality assessment is introduced and proved by comparing the calcd. and exptl. data. Based on these results, various material combinations are shown, e.g., layers made of rough particles, zeolites, activated carbon, γ-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 ma trix composites, and for special purpose applications that require corrosion and oxidn. resistance

Reticulated Replica Ceramic Foams: Processing, Functionalization, and Characterization

“…This represents the stress formed, when applying a slurry for coating and when removing the excess slurry within the replication step. [23] Additionally, beside the shear thinning (pure function of applied stress), a thixotropic behavior (function of time for the applied stress) may overlap. Due to physical (e.g., evaporation of the fluid) or chemical reactions between slurry components, the rheological properties may change during processing or storage of the dispersion.…”

“…[33][34][35][36][37][38][39][40][41] An overall adjustment of the coating thickness in combination with a high number of open windows can be realized by centrifugation after the coating process was carried out. [23,25,28,41,43] C) Green-body foams: From solidification of the coating slurry on the template foam a green foam results having a low mechanical stability. During solidification shrinkage occurs as a function of the solid load and the additive concentrations, and this may result in the formation of cracks in the green body.…”

“…[48] Boettge et al developed a coating procedure for cellular structures based on a combined dip coating and centrifugation process using shear thinning ceramic dispersions. [23] At first, the cellular structure is completely saturated with the respective coating dispersion, subsequently the excess dispersion is removed from the foam by centrifugation. A coating thickness up to 100 mm can be reached in one coating step, whereas the final layer thickness can be adjusted by the rotational speed of the centrifuge and the dispersion's yield stress and viscosity at high shear forces.…”

“…[94] A basic approach for the calculation of the coating thickness on cellular supports approximates the cumulative strut surface S strut as planar area ("plate" model; Figure 4, right). [23] The total strut surface area can be calculated according to S strut ¼ S spec. Á V foam (S spec.…”

Impact of Slurry Composition on Properties of Cellular Alumina: A Computed Tomographic Study

“…These parameters are of special interest for applications of (ceramic) foams, which are based on active coatings on cellular structures, [17] for example for catalysis [18] or energy storage and heat pumping. [19] Finally, the CT results of the alumina foams were correlated to the rheological properties of the coating slurries used for manufacturing of the respective cellular sample.…”