Alumina gel-cast foams manufactured by using agarose as gelling agent were examined in terms of microstructural, mechanical and thermal properties. The microstructural SEM measurements of alumina foams were compared with X-ray micro tomography investigations also on the pore network. Young's modulus of alumina foams was determined by impulse excitation and ultrasonic sound velocity measurements. These two independent techniques showed similar results. Gibson and Ashby's model of completely open-cell and closed-cell foams was compared with experimental data from compression tests. The thermal conductivity measurements using laser-flash analysis were correlated with the pore network in the alumina foam structure.
The influence of graphitization and composition of carbide-derived carbon (CDC) monoliths on the electrical and thermal conductivity was investigated. Carbon monoliths with varying porosities were synthesized employing biomorphous macroporous TiC and SiC as precursors. Graphitization was carried out in situ during high-temperature chlorination with and without addition of nickel, iron, and cobalt chloride to the carbide. The graphitized monoliths showed improved properties. The results demonstrate that despite graphitic carbon also glass-like carbon, stemming from the carbide synthesis, increases the thermal and electrical conductivity significantly.
The adsorption of nickel(II) ions on pristine and wet‐chemically oxidized microporous carbons is studied. The nature and acidity of the resulting oxygen functional groups are characterized by temperature‐programmed desorption and point of zero charge measurements. The maximal nickel ion adsorption capacity of the resulting high‐affinity Langmuir‐type adsorption equilibrium is strongly influenced by the oxidative pretreatment. At maximum, loadings of 7.5 wt % could be obtained for carbons showing oxygen content of 12.5 mmol g−1. A linear correlation of the ion uptake with the surface oxygen content could be deduced. In a kinetic study, it could be proved that the uptake of nickel at room temperature is a slow process and that the time for adsorption is independent of oxygen content, carbon type, and nickel loading.
Porous carbon nanotube coatings for potential solar thermal receiver applications were generated on silicon carbide via an infiltration process from an aqueous dispersion. A screening evaluation was applied to generate carbon nanotube coatings with enhanced absorption, i.e., reduced reflection of solar wavelength spectra from 2 500-500 nm. Structures with low density nanotube packing with a total reflectance <2% were fabricated from a low concentration dispersion of sterically stabilized (PVP) carbon nanotubes. Though the optical performance is lower when compared to carbon nanotube coatings generated by CVD, the filtration method offers control of the nanotube pore structure over a wide range, a greater flexibility with regards to substrate geometry and excellent up-scaling capability. B. Weisenseel, Prof. P. Greil Energy Campus N€ urnberg, F€ urther Str. 250, 90429, N€ urnberg, Germany [**] The authors thank the Energie Campus N€ urnberg for providing services and facilities and financial support through the "Bavaria on the Move" initiative of the state of Bavaria. Furthermore, support from DFG Reinhart Koselleck project GR 961/32 and DFG FE 1209/1 is gratefully acknowledged. 624 wileyonlinelibrary.com
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