Environmental Engineering Reference
In-Depth Information
Fig. 16
Left Pore network of replica foam and right combined replica and direct foaming foam
In a combined approach, a macrocellular foam was manufactured by a reticu-
lation process from preceramic polymers having a cell size of about 4 mm, and the
cells were
filled with a direct-foamable preceramic polymer slurry. In the sub-
sequent foaming process, the cell size of the
“
lled
”
foam was retained and a
secondary pore system was formed with signi
1mm
in diameter (Ceron-Nicolat et al.
2010
). Those hierarchical structures are of
increasing interest for hosting active materials including applications for heat
storage or heterogeneous catalysis. Figure
16
shows the connectivity and the
structure of foams from microtomography investigations for the macrocellular foam
(left) and the hierarchical foam (right).
In another approach, cylindrical silicon oxycarbide foams with a radial gradient
in pore size were manufactured by an extrusion process of a preceramic polymer
(Ceron-Nicolat et al.
2012
). The inner material possessed a cell size of
cant smaller cells of about 0.5
-
200
µ
m,
*
and the cells close to the surface had a cell size of
m. Those materials are
candidates for high-temperature stable lightweight materials and systems.
20
µ
*
2.3.2 Zeolite-Coated PDC Foams
Zeolites and zeolite-like structures are of special interest for a broad range of
applications. Due to the combination of pore geometry and small pore diameter, the
regular three-dimensional pore system provides a large internal surface area (hun-
dreds of m
2
g
−
1
). In conjunction with the chemical composition, the surface
properties of the particular zeolite type can be tailored for a large number of
separation, sorption, and catalytic processes. As a result, zeolites are widely used in
a variety of energy-related applications including petrochemical industry, for
exhaust gas and waste water cleaning and also for thermochemical energy storage.
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