New form of carbon dioxide: amorphous

Only carbon from the Group 14 elements forms stable double bonds with oxygen under normal conditions. When frozen, carbon dioxide is known as "dry-ice". A non-molecular single-bonded crystalline form of carbon dioxide (phase V) exists at high pressure according to Italian and French researchers.1

Amorphous forms of silica (a-SiO2) and germania (a-GeO2) are known at ambient conditions but only recently has an amorphous, silica-like form of carbon dioxide, a-CO2. This is labelled a-carbonia and made by compression of CO2 at room temperature at pressures between 40 and 48 GPa (that's a staggering 400-500 thousand atmospheres).

During this compression, infrared spectra at temperatures up to 680 K show the progressive formation of C–O single bonds and the simultaneous disappearance of all infrared bands associated with molecular CO2. Raman and synchrotron X-ray diffraction measurements confirm the amorphous character of the CO2. Vibrational and diffraction data for a-SiO2 and a-GeO2 are closely related and calculations also suggest shows that a-CO2 is structurally homologous to a-silica (a-SiO2) and a-germania (a-GeO2).

This research helps to understanding the nature of the interiors of gas-giant planets where carbon dioxide may be squeezed at very high pressures. Maybe it could be used to make very hard glass because it is expected to be very stiff rather like diamond. The researchers ponder whether "small amounts of these new glasses could be of interest for technology applications like hard and resistant coatings for micro-electronics, for example."

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