Role of Capillary Condensation in Physical Adsorption

Abstract

THE study of physical adsorption in the past decade has been dominated by the theory of multiplayer formation put forward by Brunauer, Emmett and Teller^1,2. Despite quantitative limitations, the theory explains the sigmoid shape of isotherms obtained normally for adsorption on free surfaces. In the case of porous solids, it suggested that pore diameters furnish an upper limit (n) to the number of multilayers, and derived appropriate n-limited equations. Modified forms of these equations were later suggested by Brunauer, Deming, Deming and Teller³, by Anderson^4,5, and by Pickett⁶. The fundamental point of all of these equations is that a pore becomes filled by building up n layers of adsorbed molecules, thereby obviating the need for postulating capillary condensation.