Peculiarities of thermodynamic behaviors of xenon adsorption on the activated carbon prepared from silicon carbide

An activated carbon prepared from silicon carbide by thermochemical synthesis and des-ignated as SiC‐AC was studied as an adsorbent for xenon. The examination of textural properties of the SiC‐AC adsorbent by nitrogen vapor adsorption measurements at 77 K, powder X‐ray diffrac-tion, and scanning electron microscopy revealed a relatively homogeneous microporous structure, a low content of heteroatoms, and an absence of evident transport macropores. The study of xenon adsorption and adsorption‐induced deformation of the Si‐AC adsorbent over the temperature range of 178 to 393 K and pressures up to 6 MPa disclosed the contraction of the material up to −0.01%, followed by its expansion up to 0.49%. The data on temperature‐induced deformation of Si‐AC measured within the 260 to 575 K range was approximated by a linear function with a thermal expansion factor of (3 ± 0.15) × 10 K . These findings of the SiC‐AC non‐inertness taken together with the non‐ideality of an equilibrium xenon gaseous phase allowed us to make accurate calculations of the differential isosteric heats of adsorption, entropy, enthalpy, and heat capacity of the Xe/SiC‐ AC adsorption system from the experimental adsorption data over the temperature range from 178 to 393 K and pressures up to 6 MPa. The variations in the thermodynamic state functions of the Xe/SiC‐AC adsorption system with temperature and amount of adsorbed Xe were attributed to the transitions in the state of the adsorbate in the micropores of SiC‐AC from the bound state near the high‐energy adsorption sites to the molecular associates. −6 −