1992 Volume 43 Issue 7 Pages 706-711
The size of surface pores in anodic alumina on aluminum plates, which is considered to be fairly uniform, was analyzed by adsorption experiments using krypton and n-butylbenzene vapor. The total surface area of anodic alumina samples, including the inner surface area of the pores, was estimated by the Kr/BET method, and the external surface area of the samples, excluding the inner surface area of the pores, was estimated by the “gradient method” applied in the range of 40%∼60% of relative pressure of the adsorption isotherms of n-butylbenzene vapor. For both of the adsorbate gases the samples had a significant hysteresis loop on the adsorption isotherms due to the condensation of the adsorbates into the surface pores. The total pore volume of the surface was estimated by the condensation quantity assumed from the height of the hysteresis loop for each adsorbate gas. The mean pore diameter was estimated from the total pore volume of the surface and the inner area of the pores, which was estimated from the difference between the total surface area and the external surface area of the samples. The mean values of pore diameters (6.9nm) obtained using the two adsorbates agreed with each other, and also agreed well with the values expected from the conditions of the anodic oxidation. The vapor pressures at which adsorption increased abruptly and the capillary condensation into the pores began also agreed with the values calculated from the Kelvin equation for capillary condensation using the pore radius and the surface tensions of the adsorbates.
