Calorimetric study on pure and KOH-doped argon clathrate hydrates

Pure and KOH (x=1.3×10^?3)-doped argon clathrate hydrates were synthesized in an adiabatic high-pressure calorimetric cell from one mole of water and 200 MPa of Ar gas. The heat capacities of the hydrates were measured from 12 to 130 K. No anomaly was found in the pure sample but a glass transition considered to be related to a proton-configurational mode of the host hydrogen-bonded lattice was observed for the first time at 55 K in the doped sample. Comparison with the results on pure and KOH-doped tetrahydrofuran clathrate hydrates indicated that the thermodynamic properties of a hydrogen-bonded system depend on the kind of guest molecule. The heat capacity of argon in the hydrate cages was adequately analyzed with the one-dimensional Pöschl-Teller potential as used in the Ar-β-quinol clathrate and the addivity of heat capacities of the guest and host was shown to be valid in the temperature range 12–130 K.