Strategy development for the coating of open-pore structured, nanoporous materials with low density

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A coating is advantageous for many applications of porous materials, for example to protect substances encapsulated within the porous structure from moisture or to achieve mechanical stabilization of the porous network during storage and transport. The aim of this project is to develop a strategy for the coating of open-pore structured, nanoporous materials with low density using organic aerogel particles as model material. In this coating process the sensitive pore structure of the aerogels should not be damaged by penetration of the sprayed liquid solution or melt. Therefore it should be investigated whether processing using the solution or the melt is more suitable for the coating of open-porous materials. In the first step, the production of aerogel particles with different particle sizes and densities is investigated. Spherical gel particles are produced in the liter scale using the emulsion gelation method and the JetCutter apparatus to achieve the size range between a few micrometers and 2 mm. The formed gel particles are subsequently supercritically dried resulting in highly porous aerogel particles. The coating of the produced aerogel particles is performed in a prismatic spouted bed apparatus. The fluidization behavior of these extremely light, cohesive particles with different density (particle porosity) and particle diameter is tested and classified into the Geldart diagram. For the coating of the particles, the optimum process conditions should be found in order to achieve a core-shell structure while preserving the pore structure of the aerogel particles. In addition, the fluidization and the entire process chain of spraying - drying - shell formation will be modeled and optimized by means of coupled CFD-DEM simulations.