Correlation of the equilibrium adsorption isotherms of low temperature cryodeposits

The applicability of several existing adsorption theories for predicting the equilibrium isotherms for. the sorption of hydrogen by carbon dioxide cryodeposits has been examined in the pressure range from 10⁻⁸ to 10⁻³ torr (1 torr = 133 N m⁻²). It is demonstrated that the H₂ sorption capacity of CO₂ frost cryosorbents at temperatures between 12 and 20 K may be accurately predicted by an equilibrium isotherm equation proposed by Dybinin and Raduschkevich. This equation is then used to calculate families of sorption isotherms for CO₂ frosts formed at various conditions and consequently having different structures. These results may be used to estimate the H₂ capacity of cryosorption pumping systems which would employ CO₂ frost as a cryosorbent. The applicability of this semi-empirical method to other frost sorbent-sorbate combinations is also reviewed.