Impregnation of Calcium Chloride into Alumina Thin Film Prepared by Oxalic Acid Anodizing

Abstract

In the present study, a calcium chloride-oxalic acid anodized alumina composite was proposed as a sorbent of water vapor for the application to adsorption chiller. CaCl₂-anodic alumina composite sorbents were prepared by anodic oxidation of an aluminum plate in an oxalic acid bath, following the widening of pores in anodic oxide films with a sulfuric acid solution and the impregnation of saturated aqueous solution of CaCl₂ into the pores at a reduced pressure. As a result, the alumina films prepared in an oxalic acid bath had numerous large pores, and their porosities were significantly larger than those of sulfuric acid-anodized alumina films. The amounts of CaCl₂ impregnated into the alumina films were a function of the apparent densities of the films, and the maximum CaCl₂ content was 39.7 wt%. The CaCl₂-anodic alumina composites were capable of sorbing water vapor even in the relative pressure range below 0.3. With higher doses of CaCl₂ contained by the alumina film, a larger amount of water vapor was sorbed by the composite. Furthermore, the CaCl₂-oxalic acid anodized alumina composite showed a fast water sorption rate like commercial silica-gel particles.