Deposition of thick, rigid and size-controlled silica particle layer on aluminum sheet for water vapor adsorption

Toward the development of a new adsorbent heat exchanger of adsorption chillers, silica-coated aluminum sheets were prepared by the combination of sol-gel and electrophoretic deposition techniques. Silica sols were synthesized by the hydrolysis of tetraethoxysilane precursor in an ethanol solution, and then a silica layer was directly formed on an aluminum sheet by electrophoretic deposition of the silica sols. The silica-coated aluminum sheets were subjected to the aging treatment in an ammonia water bath with a DC electric field. This aging treatment was found to be very effective to form rigid silica layer on aluminum sheet. It was found that the obtained layer was composed of monodisperse and spherical submicron-sized silica particles. Sodium dodecyl sulfate (SDS) in the silica sol solution played an important role in controlling the deposited amount of silica particles as well as their sizes. The particle size increased from 0.10 to 0.83 µm with an increase in SDS concentration. For the silica-coated aluminum sheet prepared at a pH value of 10.6 and a SDS concentration of 0.05 mass%, the deposited amount reached a maximum value of 19.8 mg cm−2, which was much higher than those reported by Kishida et al. (1994). The prepared composites were evaluated for the characteristics of water vapor adsorption through volumetric experiments. The results of adsorption experiments showed that the composite with a higher silica content adsorbed a larger amount of water vapor in the relative pressure range below 0.3.