A THEORY OF MULTILAYER ADSORPTION ON ROUGH SURFACES IN TERMS OF CLUSTERING AND MELTING BET PILES

An equation is proposed on theoretical grounds for the description of equilibrium adsorption of vapours below their critical temperature on solid adsorbents. Like in the Brunauer-Emmett-Teller (BET) theory, eac h surface site is described as the origin of an adsorbed pile; differe ntly from the BET theory, however, the piles are allowed to undergo a branching process when the equilibrium pressure is increased; vapour c ondensation is assumed to occur when all the available space is filled . This growth is described by an isotherm behaving as the BET equation in the monolayer region, as the Anderson or Brunauer-Skalny-Bodor ext ension of the BET equation just above the monolayer, and as the Frenke l-Halsey-Hill equation at higher coverage. For suitable choice of its free parameters, the proposed equation accounts for all isotherms of t ype I, II and III of Brunauer classification. (C) 1998 Elsevier Scienc e B.V. All rights reserved.