DYNAMIC COMPRESSION EFFECTS AND PHASE TRANSFORMATION KINETICS OF FUNDAMENTAL MOLECULES

H2O and N2 play vital roles in the universe we find ourselves in and both have a set of complex phases and phase transition kinetics. H2O can directly solidify into metastable ice VII within the stability field of ice VI. Due to the presence of hydrogen bonding (HB), water displays a myriad of properties and is drastically affected by the rate pressure is applied or removed. Utilizing a dynamic-diamond anvil cell (d-DAC) combined with time-resolved x-ray diffraction (TR-XRD), time resolved ruby luminescence (TRR), and high-speed microphotography, it was found that the solidification pressure of metastable ice VII has a potential sigmoidal dependence upon compression rate with a turnover compression rate of roughly 80 GPa/sec. The preferential crystallization of ice VII in the phase region of ice VI is due to the increased nucleation rate of ice VII over ice VI at 1.77 GPa driven by the interfacial energy difference between the liquid and solid phases along with the change in Gibbs’ free energy of solidification. It is also found that the compression rate greatly affects the solid-solid phase transition between ice VI and VII but does not affect the liquid-solid transition between water and ice VI as much and minimally affects the solidification of β-N2 along with the solid-solid transition from β- to δ-N2 . This study also found that there was no significant change in c/a ratio with increasing pressure, even at the highest compression rates observed. Lastly, a third phase transition was found to occur after metastable ice VII transforms into high-density amorphous ice (HDA), which could be a disordered hydrogen bond network (HBN) configuration of ice VII forming out of HDA facilitated by the decoupling of the oxygen movement and reorientation of the H2O molecule.