The surface area of graphite calculated from adsorption isotherms and heats of wetting experiments

Abstract

The heat of wetting of a graphite has been determined in four different liquids, methyl alcohol, isopropyl alcohol, benzene and toluene. The surface area of the material has been calculated from vapour adsorption isotherms determined gravimetrically using the same liquids and the B.E.T. theory. From the two sets of results the heat of wetting per square centimetre of the graphite surface has been obtained. The surface area calculated from the vapour adsorption isotherms show reasonable agreement with the surface area determined by low temperature nitrogen adsorption, indicating that pores which are accessible at room temperatures are also accessible at the lower temperature. The isotherms are type II with slight hysteresis and both adsorption and desorption branches of the hysteresis loops are sloping. It is thought that this could result from particle-particle adhesion under the influence of the adsorbed film and need not necessarily be a reflection of a porous character in the graphite particles themselves. This suggests that it is reasonable to accept the graphite sample as a suitable material for correlating adsorption and heat of wetting data, leading to the determination mentioned previously of the heat of wetting per square centimetre for each of the liquids used. The heat of wetting calculated in this way for methyl alcohol is then compared with other published data.