2-DIMENSIONAL FREEZING OF NITROGEN OR ARGON ON DIFFERENTLY GRAPHITIZED CARBONS

On a set of differently graphitized carbon blacks (Sterling heated between 1500 and 2700°C), chosen to reproduce, in some respects, the set used in 1954 by Beebe and Young (J. Phys. Chem. 58, 93) in their famous experiments, adsorption microcalorimetry at 77 K gives experimental evidence of a two-dimensional fluid → solid phase change at the completion of the argon or nitrogen monolayer. That phenomenon (which is confirmed by a slight substep of the isotherms) develops earlier (i.e., on a less graphitized surface) in the case of argon than in the case of nitrogen: This is explained by the epitaxial crystallization of nitrogen which makes it very sensitive to the size of the graphitic sheets. © 1979.