Evaluation of microporosity, with special reference to a carbon black

Abstract

If an adsorbent yields a type II isotherm (BDDT classification), then the value of the monolayer capacity, and therefore of the specific surface, calculated from the isotherm will be incorrect unless the micropore contribution is allowed for. A method for the evaluation of the micropore contribution of a carbon black to the adsorption isotherm of nitrogen at –195°C is described. The micropores are filled with nonane at –195°C by adsorption from the vapour phase, and the excess pumped off at room temperature. The adsorption isotherm of nitrogen at –195°C is determined on the sample, both before and after thus filling the micropores. The volume of the micropores is then given by the distance between the (parallel) portions of the two isotherms corresponding to the multilayer region.