Ice-nine

Those of you who have read Cat’s Cradle by Kurt Vonnegut may be familiar with the metastable form of solid water, ice-nine. In the book, when a crystal of ice-nine contacts liquid water, it acts as a seed crystal causing the formation of more ice-nine.

While ice-nine is a pure fiction, the molecular solid CO2-II is not. This compound forms a layered polymeric structure at pressures nearly 600,000 times atmospheric pressure and at temperatures around 600 Kelivn. Chemists are interested in this phase because it exhibits the interesting physical properties of “super-hardness.” The researches that conducted this study also believe their data predicts the existence of an amorphous form of CO2 with a structure similar to silicon dioxide. This phase forms under extremely high pressure (80 GPa) and at a temperature below 25ºC.

This research was done with a computer simulation method known as “metadynamics.” The researches combined data from the simulation with quantum mechanical calculations and interpreted the results.

The pressures at which these phases form are found only in the Earth’s mantle, where large amounts of oxidized carbon are believed to exist. Therefore, these and future results may increase our understanding of mantle chemistry.