High pressure kinetics studies of water solidification in dynamic-DAC

Abstract

The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H 2O phases attests the versatility of hydrogen bonded network structures that include kinetically stable amorphous ices. In addition, natural gas hydrates are observed upon cooling and/or pressurization. The structures of gas hydrates are quite different from ices, yet guest molecules are enclathrated inside hydrogen bonded water cages. Hence, the presence of small impurity molecules can affect strongly the behaviours of hydrogen bonding and alter the phase diagram and phase boundaries of H2O. In this paper, we report the effect of methane impurity on solidification and melting of H2O under dynamic loading conditions. The presence of impurity mainly affects the growth rate of metastable ice VII, slowing down from 1.4 m/s in pure H 2O to 0.26 m/s in impure H2O, neither the occurrence of metastable ice VII nor the melting of ice VI.