Magnesium carbonate–phosphate glass

Magnesium carbonate–phosphate glasses have been prepared by quenching melts in the MgO–P2O5–CO2 system at 1400–1550 °C and 2.0 GPa, using a piston-cylinder apparatus. Glass compositions extended along the join Mg3P2O8–MgCO3 from 0.167 to 1.0 M CO3/P2O5. Carbonate contents were confirmed using a novel procedure based on the intensity of the π∗ peak of carbon K  -edge XANES spectra. FTIR spectra show that only one carbonate environment is present in the glasses, and suggest that the glass structure consists of a network of isolated carbonate (CO32-) and orthophosphate (PO43-) anions interconnected by Mg2+ cations. The addition of 5 wt% water to the starting composition did not result in significant change in FTIR spectra, other than in the hydroxyl stretching region. However, a systematic upward shift in the X-ray scattering maximum for the wet glasses remains to be explained.