Coating of Open Cell Foams

Abstract

The interior surfaces of three-dimensional open cell foams were coated by a combination of dip coating and spin coating. Glycerol/water solutions were used as model Newtonian liquids, and the coating processes were studied on open cell carbon foams with 10 or 30 pores per inch (PPI). The amount of liquid retained in the foam structures after dip coating increased with withdrawal speed and coating viscosity, as expected from the conventional understanding of dip coating onto nonporous substrates such as flat plates and rods. However, the liquid retention and hence average coating thickness increased with surface tension, a result counter to the observation with coating onto nonporous substrates. Pockets of liquid were observed after dip coating and results with coatings of alumina suspension showed that after drying, the trapped liquid can block pore windows. Spinning the foams after dip coating resulted in uniform liquid distribution and uniform coatings. Foams were placed in a special apparatus and rotated using a commercial spin coater. The liquid layer thickness decreased with spinning time and rotational speed, and increased with the liquid viscosity, results consistent with spin coating theory. The coating thickness after spinning was not affected by the initial dip coating procedure. The dip and spin process was also used to create γ-alumina and zeolite coatings, which are of interest for catalysis applications.