Water and gallium at absolute negative pressures. Loci of maximum density and of melting

Several physical properties of liquids as well as those of the coexistence between liquid and solid can be determined at absolute negative pressures. Examples for this include thermal pressure coefficients, loci of temperatur e of maximum density, melting lines, speed of propagation of low-intensity sound waves, and (p, T, x) conditions of occurrence of liquid/liquid phase separation. Three model temperature-pressure cycles, which allow for the me asurement of temperature-pressure conditions of the occurrence of maxima of liquid density, negatively sloped fusion lines, and the upper critical sol ution temperature (UCST) of liquid solutions in these metastable regimes ar e described. A new apparatus for measuring negative pressures was developed . The temperature and pressure are determined within an uncertainty of +/-0 .05 degreesC and +/-5 bar, respectively. Water and heavy water have been us ed as testing systems with respect to the location of their temperatures of maximum density (TMD) loci. Empirical equations of state whose parameters have been fitted to experimental data located in the normal positive pressu re region have proven to extrapolate well to the negative pressure regime. Furthermore, an attempt was made to use SAFT in order to provide a more the oretically founded framework. Preliminary results for gallium have shown th at a TMD exists 45 K inside the supercooled regime, and that the continuati on of its melting line down to -80 bar evolves with a slope of -515 +/- 25 bar.K-1.