Water: Anomalous compressibilities to 1.9 kbar and correlation with supercooling limits

Abstract

A new high pressure volumetric technique, which employs a fine glass capillary as joint sample chamber and pressure vessel is described. Because of the small samples used, it is suitable for supercooled liquid studies. The compressibilities κT of water and of D2O have been determined over the applied pressure range 0.1–190 MPa (1–1900 bar) at temperatures in the range of 25–30°C. The anomalous low temperature increases in κT reported earlier for H2O at 1 bar are found at higher temperatures in D2O, as expected. In both liquids, increases in pressure cause the anomalous regions to be displaced to lower temperatures. The displacement per unit pressure change increases with increasing pressure. As found previously, the low temperature data conform to an empirical equation κT=A (Ts/T−1)−γ where Ts is a characteristic temperature now found strongly dependent on pressure. High pressure data are inadequate to yield both Ts and γ parameters reliably but, when γ is assigned a pressure-independent value, the best fit Ts values vary in each case with pressure in a manner strikingly similar to that of the homogeneous nucleation temperature, confirming a previously suspected relation between the two quantities. Preliminary attempts to separate the total compressibility into ’’normal’’ and ’’anomalous’’ parts suggest that the exponent γ is close to unity, as found previously for the anomalous component of the expansivity.