Characterization of surface activity

In order to achieve a better understanding of the reinforcement mechanism o riginal furnace blacks differing in DBP-number and specific nitrogen surfac e area as well as of graphitized furnace blacks have been examined in view of their geometrical surface roughness. The adsorption isotherms of Argon a nd Nitrogen at 77 K were evaluated by using the fractal Frenkel-, Halsey-, Hill- theory (FHH-theory), which describes the geometrical surface roughnes s by the surface fractal dimension D-s. (D-s = 2: smooth surface; D-s = 3: infinete rough surface). All examined original furnace blacks have the same roughness (D-s approximate to 2,6) beyond a length scale of z less than or equal to 6 nm. Therefore the different reinforcement potential of these bl acks cannot be explained by a variable surface roughness. Graphitization re duces the roughness beyond the length scale of z less than or equal to 0,8 nm to D-s approximate to 2,3. These results are in accordance with ealier o bservations obtained by the independent yardstick-method, which evaluates t he surface fractal dimension from adsorption isotherms of gases of differen t size (Ethylene, Ethane, Propane, Iso-Butane).