Gradual crossover in molecular organization of stable liquid H{sub 2}O at moderately high pressure and temperature
- Department of Chemistry, The University of British, Columbia, Vancouver, BC, Canada V6T 1Z1, and Suitekijuku, Vancouver, BC, Canada V6R 2P5 (Canada)
- NSM, Research Unit for Functional Biomaterials, Roskilde University, Roskilde, Denmark DK-4000 (Denmark)
- Research Center for Structural Thermodynamics, Osaka University, Toyonaka, Osaka, Japan 560-0043 (Japan)
Using the literature raw data of the speed of sound and the specific volume, the isothermal compressibility, κ{sub T}, a second derivative thermodynamic quantity of G, was evaluated for liquid H{sub 2}O in the pressure range up to 350 MPa and the temperature to 50 ºC. We then obtained its pressure derivative, dκ{sub T}/dp, a third derivative numerically without using a fitting function to the κ{sub T} data. On taking yet another p-derivative at a fixed T graphically without resorting to any fitting function, the resulting d{sup 2}κ{sub T}/dp{sup 2}, a fourth derivative, showed a weak but clear step anomaly, with the onset of the step named point X and its end point Y. In analogy with another third and fourth derivative pair in binary aqueous solutions of glycerol, dα{sub p}/dx{sub Gly} and d{sup 2}α{sub p}/dx{sub Gly}{sup 2}, at 0.1 MPa (α{sub p} is the thermal expansivity and x{sub Gly} the mole fraction of solute glycerol) in our recent publication [J. Solution Chem. 43, 663-674 (2014); DOI:10.1007/s10953-013-0122-7], we argue that there is a gradual crossover in the molecular organization of pure H{sub 2}O from a low to a high p-regions starting at point X and ending at Y at a fixed T. The crossover takes place gradually spanning for about 100 MPa at a fixed temperature. The extrapolated temperature to zero p seems to be about 70 – 80 °C for points X and 90 – 110 °C for Y. Furthermore, the mid-points of X and Y seem to extrapolate to the triple point of liquid, ice Ih and ice III. Recalling that the zero x{sub Gly} extrapolation of point X and Y for binary aqueous glycerol at 0.1 MPa gives about the same T values respectively, we suggest that at zero pressure the region below about 70 °C the hydrogen bond network is bond-percolated, while above about 90 ºC there is no hydrogen bond network. Implication of these findings is discussed.
- OSTI ID:
- 22299770
- Journal Information:
- AIP Advances, Vol. 4, Issue 9; Other Information: (c) 2014 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 2158-3226
- Country of Publication:
- United States
- Language:
- English
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