Interaction of water molecules with nongraphitized and graphitized carbon black surfaces

Surface characteristics of nongraphitized carbon black (S-II) and graphitized carbon black (S-III) were investigated by analyzing the adsorption isotherms of Kr, N 2 , and H 2 O. S-II was prepared by heating Spheron 6 (S-I) at 1273 K in vacuo, and S-III was prepared by graphitizing Spheron 6 (S-I) at 2973 K in an argon atmosphere. It was found from the Kr isotherms that the surface of S-II was heterogeneous, while that of S-III was homogeneous. The t-plot of the N 2 isotherm showed that S-II was nonporous. However, the minute microporosity was detected in S-II from the comparison plot of the water isotherm. The size of the micropores present in S-11 may be larger than 0.22 nm (the water molecule size) and smaller than 0.43 nm (the nitrogen molecule size). The adsorption isotherms of water vapor on S-III were measured at 283, 298, and 308 K in the range of Γ = 0.0004-0.6 H 2 O/nm 2 . The differential enthalpies (ΔHs) and the differential entropies (ΔS s = S s - S L ) of the water molecules adsorbed on the S-III surface were computed using the water isotherms. From the curves of ΔR s , ΔS s , vs coverage, it has been shown that the adsorbed water molecules start to make the liquid-like clusters from low coverage and that mobility of the adsorbed water molecules is very large below Γ = 0.02 H 2 O/nm 2 .