Open Collections

The thermodynamic behaviour of super-cooled water

University of British Columbia

A new statistical-mechanical, analytical equation of state for water is developed based on the Song and Mason equation of state and Poole et al.'s simple model of the free energy of open tetrahedral hydrogen bonds. Following Weeks et al. (1971b,a) the intermolecular potential is divided at its minimum into regions of attractive and repulsive force. Repulsive forces are modelled accurately using the algorithm of Ihm et al. (1991), and the attractive forces are modelled by (non-open tetrahedral) hydrogen bonds that contribute both energy and entropy to the free energy of water. Open tetrahedral hydrogen bonds are modeled explicitly using a simplified partition function. The resulting equation of state is 20 to 30 times more accurate than any equivalent simple cubic equation of state over a wide range of pressures (0.1 -» 3000 bar) and temperatures (—34 —> 1200 °C) including the supercooled region. A further extension of the equation of state down to virtually 0 K is possible because of its strong statistical-mechanical basis. The new equation of state predicts a second liquid-liquid critical point at pc — 101 kbar, pc> = 1.03 (g cm- 3 ) and Tc = 222.5 K. A liquid-liquid spinodal bounds a region in which a low-density (p « 0.93 g cm- 3 ), open tetrahedrally bonded liquid and a high-density (p w 1.1 —> 1.5 g cm- 3 ) liquid may exist. A detailed analysis of the physics of homogeneous nucleation using the density and entropy of water calculated from the new equation of state reveals that the homogeneous nucleation temperature above 1 kbar is determined solely by a high-density —> low-density phase transition.

Thesis/Dissertation

application/pdf

2009-02-14

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

http://hdl.handle.net/2429/4593

Physics

University of British Columbia

UBCV

DSpace