The structure of Pyrex® glass investigated by correlation NMR spectroscopy.

ABSTRACT

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).