Volumetric and derived thermal characteristics of liquid D2O at low temperatures and high pressures

Abstract

Using a refinement of a capillary technique described earlier precise PVT data on D2O between 0.1 and 140 MPa and down to −30 °C have been obtained, and the pressure dependence of the volumetric behavior in the vicinity of the well-known density maximum has been examined. The ’’sharpness’’ of the density maximum, defined by dα/dT at α=0 K−1, decreases with increasing pressure in a simple linear manner. Extrapolations suggest that at about 250 MPa the density maximum would have the same sharpness as that known for the tetrahedral network liquid SiO2, but would occur at temperatures too low to be observed. A relation between volumetric anomalies and bridge-bond angles in liquids with tetrahedral network structures is suggested. The volumetric data are used to derive the effect of high pressure on the constant pressure heat capacities. From these it is argued that, on extended supercooling at 2 kbar, water could pass normally into the glassy state at about 140 K without encountering the entropy paradox which exists for water at normal pressures.