The structure of Pyrex® glass investigated by correlation NMR spectroscopy

The structure of the important technological glass Pyrex® was investigated by 1D- and 2D-correlation NMR techniques. Its local order was analysed in a first step by 1D ²³Na, ²⁷Al, ¹¹B and ²⁹Si MAS-NMR performed at 9.4 and 18.8 T. In a second step, its medium range order was documented using homo- and, for the first time, hetero-nuclear correlation NMR techniques: (i) the presence and the nature of BOB bonds were analysed using 2D ¹¹B DQ-SQ map; (ii) the silicate speciation was probed using 2D ²⁹Si/X (X = ¹¹B, ²³Na and ²⁷Al) D-HMQC maps and (iii) the ²⁷Al/¹¹B interaction was studied using TRAPDOR-NMR experiments. Altogether, the set of NMR data was used to extract accurate NMR parameters, to rule out the presence of diborate and danburite superstructural units and to provide an updated structural model based on B³ based groups attached to a T⁴ network (T = Si, B, Al).