On physical adsorption: X. Adsorbed monolayers of argon and nitrogen on boron nitride and on a graded series of partially graphitized carbon blacks

Abstract

Low-pressure adsorption isotherms of argon and nitrogen at 77.8° and 90.1°K. were measured on members of a graded series of a carbon black, which had been partially graphitized in an inert atmosphere at temperatures of 1000, 1500, 2000, and 2700°C. An increasing homogeneity of the surface accompanies graphitization and is reflected in a number of adsorption phenomena, all of which gradually become more pronounced with increasing degree of surface homogeneity: ( a) the two-dimensional van der Waals' equation provides a description of the isotherm over a greater range of surface concentrations; ( b) the two-dimensional critical temperature of the adsorbate increases regularly toward the theoretical value expected of an ideally uniform substrate; ( c) the mobilities of the adsorbed monolayers correspond over an increasingly greater range of surface concentration to that of a two-dimensional gas on a uniform substrate. A sample of boron nitride was also used as adsorbent for monolayers of argon and nitrogen at 77.8 and 90.1°K. A comparison of the results for boron nitride with those for the carbon black series shows that the boron nitride surface would correspond to a carbon black of the present series graphitized at 1800°C.