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Silicon carbonate phase formed from carbon dioxide and silica under pressure

Santoro, Mario, Gorelli, Federico, Haines, Julien, Cambon, Olivier, Levelut, Claire, Garbarino, Gaston
Proceedings of the National Academy of Sciences of the United States of America 2011 v.108 no.19 pp. 7689-7692
X-ray diffraction, carbon dioxide, carbonates, chemistry, infrared spectroscopy, porous media, silica, silicon, temperature, thermodynamics, zeolites
The discovery of nonmolecular carbon dioxide under high-pressure conditions shows that there are remarkable analogies between this important substance and other group IV oxides. A natural and long-standing question is whether compounds between CO₂ and SiO₂ are possible. Under ambient conditions, CO₂ and SiO₂ are thermodynamically stable and do not react with each other. We show that reactions occur at high pressures indicating that silica can behave in a manner similar to ionic metal oxides that form carbonates at room pressure. A silicon carbonate phase was synthesized by reacting silicalite, a microporous SiO₂ zeolite, and molecular CO₂ that fills the pores, in diamond anvil cells at 18-26 GPa and 600-980 K; the compound was then temperature quenched. The material was characterized by Raman and IR spectroscopy, and synchrotron X-ray diffraction. The experiments reveal unique oxide chemistry at high pressures and the potential for synthesis of a class of previously uncharacterized materials. There are also potential implications for CO₂ segregation in planetary interiors and for CO₂ storage.