| 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 P[subscript cross] ~ 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 K[subscript T](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[superscript −3] K[superscript −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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