| Summary: | The density maximum of water dominates the thermodynamics of the system under ambient
conditions, is strongly P-dependent, and disappears at a crossover pressure
Pcross ~ 1.8 kbar. We study this variable across a wide area of
the T–P phase diagram. We consider old and new data of both the
isothermal compressibility KT(T, P) and the coefficient of
thermal expansion αP(T, P). We observe that
KT(T) shows a minimum at T* ~ 315±5 K for
all the studied pressures. We find the behavior of αP to also be
surprising: all the αP(T) curves measured at different P
cross at T*. The experimental data show a “singular and universal expansivity
point” at T* ~ 315 K and αP(T*) ≃ 0.44
10−3 K−1. Unlike other water
singularities, we find this temperature to be thermodynamically consistent in the
relationship connecting the two response functions.
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