Structural details of aqueous attack on a phosphate glass by ¹H/³¹P cross-polarization NMR

One- and two-dimensional heteronuclear correlation solid-state nuclear magnetic resonance experiments allow a direct study of the chemistry of water incorporation into a simple phosphate glass network. One main pathway for water incorporation into phosphate glass networks is through the formation of P-OH groups, and previous ¹H magic-angle-spinning NMR investigations of proton environments in silicate and phosphate glasses suggest that hydroxyl groups are involved in multiple hydrogen-bonding motifs with backbone units within the glass networks. The presence of multiple proton environments presents more complex structural issues for aqueous incorporation into glass systems, which have yet to be explained unambiguously. The spectral editing capabilities of two-dimensional cross-polarization NMR identify specific subunits in modified sodium phosphate glasses, and strong evidence is presented for the formation of intramolecular as well as weaker intermolecular hydrogen bonds. Using a combination of one- and two-dimensional ¹H/³¹P cross-polarization NMR studies, a total of five distinct phosphate units are identified in a near-metaphosphate glass after aqueous treatment.