CALORIMETRIC STUDY OF ICES Ih DOPED WITH ALKALI HYDROXIDES AND OTHER IMPURITIES

Heat capacities of ices Ih doped with NaOH, KF and NH4F (0.1 mol dm-3) and Ba(OH)2 (0.04 mol dm-3) have been measured between 13 K and the melting temperature. The ice doped with NaOH underwent the order-disorder transition at 72 K. The entropy of the transition depended on the sample history. The largest value, 1.41 JK-1 mol-1, obtained on the most thoroughly annealed sample represents 42 % of the residual entropy. The other three dopants did not induce the phase transition. Among the dopants hitherto studied (HF, KOH, RbOH and KOD, besides those reported here) only the alkali hydroxides are the effective catalysts for the transformation of ice Ih to the low temperature ordered phase which we call the ice XI.