Water Sorption by Carbon Fibers

The degree of crystallinity of carbon fibers (CFs) of different manufacturers has been determined by means of the Raman scattering method. A gradient "core–shell" model for the CF structure has been suggested. The element composition of CFs has been determined by means of the X-ray electron probe analysis. It has been established that the CF includes oxygen-containing groups, the concentration of which varies from 2 to 4 wt %. A fibrillar structure of the CF shell has been identified via the methods of atomic force probe microscopy and transmission electron microscopy. Longitudinal and transverse sizes of fibrils have been determined. Using the method of low-temperature nitrogen adsorption, the specific surface area, porosity, and pore sizes of CFs have been determined. Isotherms of water vapor sorption by CF within the moisture range from 10 to 95 wt % have been obtained. It has been demonstrated that, for all the studied samples, the sorption isotherms can be approximated using the Dubinin–Radushkevich equation. The sorption capacity of water vapor by CFs has appeared to significantly exceed that of nitrogen, which was associated with the presence of oxygen-containing functional groups.