If a given liquid exhibits a density maximum anywhere in its phase diagram, thermodynamic consistency dictates that such a point cannot be isolated: a density maxima locus must necessarily exist. For a fluid that does not also exhibit density minima, the pressure‐temperature projection of such a locus is negatively sloped, and can only end at a stability limit. There exist two thermodynamically consistent ways in which such an intersection can occur, and they correspond, respectively, to the highest and lowest possible temperatures at which a liquid can exhibit a negative coefficient of thermal expansion. These theoretical predictions are confirmed by experimental observations. The existence of density anomalies anywhere in a liquid's phase diagram is shown to have a profound influence in determining the shape of such a fluid's stability boundary.

Comparison of the pseudospinodal to the transition from metastability to instability in a binaryliquid mixture J. Chem. Phys. 94, 8630 (1991); 10.1063/1.460050Erratum: On the nature of the tensile instability in metastable liquids and its relationship to density anomalies [J.Tensile instability is a hitherto unexplained phenomenon whereby a metastable liquid loses tensile strength as the temperature is reduced in the vicinity of its triple point. The thermodynamically consistent behavior which must be exhibited by any liquid in the vicinity of a tensile instability displays a variety of unusual phenomena: nonanalytic density maxima, spinodal retracing, and density anomalies (negative thermal expansion coefficient) in the vicinity of the spinodal curve. Loss of tensile strength implies (and is inseparable from) density anomalies in the vicinity of the spinodal curve. This important conclusion is derived here from first principles.

The thermodynamically consistent behavior of any fluid whose tensile strength exhibits a maximum with respect to temperature (tensile instability) is derived for the case where the isochore corresponding to the fluid density at such a maximum is single branched (i.e., a metastable solution exists only for temperatures higher than the tensile instability temperature). The resulting thermal and volumetric picture is considerably simpler than for the recently derived behavior corresponding to the case where the tensile instability isochore admits metastable solutions both above and below the tensile instability temperature (doublebranched limiting isochore). Density extrema are inseparable from tensile strength maxima: a tensile instability is, in fact, the low-pressure intersection of a spinodal curve and a locus of density extrema.

Several liquids exhibit an apparent loss of tensile strength (tensile instability) as their temperature is lowered. Assuming that such substances exhibit a true minimum in the PT projections of their spinodal curves, the thermodynamically consistent behavior that follows from this hypothesis displays a variety of unusual phenomena, of which the PVT aspects have been recently discussed. If, along the tensile instability isochore, the reciprocal compressibility vanishes linearly with respect to temperature (as is the case for a van der Waals fluid near the spinodal) an unusual metastable phase transition with discontinuous entropy and thermal expansion coefficient but continuous volume must occur if this isochore admits a metastable solution below the tensile instability temperature. The form of the specific heat divergence, as well as the equations of phase diagram loci of constant correlation length follow from the nature of the PVT surface in the vicinity of a tensile instability.

Erratum: Cluster formation of hydrogen cyanide in solid and liquid CCl4 matrices [J.On the nature of the tensile instability in metastable liquids and its relationship to density anomalies