The surface properties of carbon—III the process of activation of carbons

Abstract

The adsorption has been studied of nitrogen, carbon dioxide and ethyl chloride upon activated carbons prepared from polyvinylidene chloride. The BET equation and the Potential Energy equation as modified by Dubinin have been used to interpret results. The changes taking place on the surface of carbons following progressive activation have been followed by electron microscopy using the methods of transmission and replication. It is concluded that the surface areas developed in carbons by activation with, e.g. carbon dioxide, are only of the order of 1000 m 2g −1. The high adsorptive capacity which can be developed in certain carbons is attributed to the development of etch pits, of the size of transitional pores which are capable of filling reversibly with liquid adsorbate. The mode of development of these etch pits is illustrated. It has been shown that the adsorption of carbon dioxide on both activated and unactivated carbons and of ethyl chloride on the activated carbons followed monolayer statistics up to about 0–80 of a monolayer. Certain anomalies met with here and mentioned in the literature are explained. Finally, an attempt has been made to present a physical picture of processes occurring during activation.