Structural studies in aluminophosphosilicate glasses and in cold-pressurized borosilicate glasses by Nuclear Magnetic Resonance in the solid state

Abstract

P]/[Si] ratios, was formed. This structure is likely suppressed by the strong interaction between phosphorus and aluminum, which was measured by 27 Al-31 P double resonance dipolar recoupling experiments. Dipolar recoupling techniques also facilitated the analysis of the 31 P MAS-NMR spectra in terms of two distinct components with different chemical shifts: one interacting more strongly with Na, the other one interacting more strongly with Al. The NMRbased structural information can provide insights about the non-linear composition dependence of the weathering resistance of the glasses. In (iii) the cold pressurized borosilicate glasses, 11 B MAS-and 23 Na MAS-NMR illustrated together a counterintuitive structural effect: the average B coordination number decreases upon compression. This effect exposes a behavior not previously reported in the literature: the applied pressure induces a closer approximation between Na + ions and oxygen species bridging between tetrahedral boron and silicon, causing a breaking in B(IV)-O-X (X = B, Si) linkages. As a result, new B(III) units are formed, as well as new non-bridging oxygens predominantly attached to silicon (later compensated by Na + ions). These results clearly document an insightful detailed structural picture provided by solidstate NMR, which was used to suggest possible and multiple structural origins for each macroscopic effect investigated.