Effect of catalyst and substrate on the moisture diffusivity of silica-aerogel-coated metal foams

Silica aerogel desiccants have good adsorption and desorption characteristics and commonly are deployed on metallic or non-metallic substrates as thin coatings in typical dehumidifying applications. The dehumidifying performance of desiccant coated on substrates often depends on the micro-structure of desiccants, as well as on the characteristics of substrates, such as surface area. The current study focuses on the preparation and adsorption/desorption performance evaluation of various types of silica aerogel coatings on different metal foam substrates. The silica aerogel coated metal foam samples have been prepared by dip coating process using different basic and acidic catalysts, followed by the super-critical drying. The microstructures of aerogel coating obtained by scanning electron microscopy, are compared to porous structures of solid desiccant blocks prepared using the same method (catalyst). A new automatic dynamic vapor sorption method is used to determine the mass diffusion coefficient of silica aerogel coated foam samples. SEM image analysis is used to determine the geometrical parameters (pore diameter, ligament diameter) of coated and uncoated foams of 5, 10 and 20 PPI for data reduction. The impact of substrate type and microstructure of the coating, which depends on the catalyst used in sol-gel process on the mass diffusivity, has been evaluated. The results of this study can be used in the development and performance evaluation of various dehumidification applications containing silica aerogels deployed as thin coatings.