Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and ²⁷Al MAS NMR lineshape analysis

Abstract

Abstract The recent progress in NMR of glasses is demonstrated using both traditional and improved two‐dimensional (2D) NMR techniques. A novel approach for measuring connectivities Q n units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27 Al NMR investigations in mullites and Na 2 O‐SiO 2 ‐Al 2 O 3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO 4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na 2 O‐Al 2 O 3 ‐SiO 2 glasses we could prove the presence of two AlO 4 sites with Al being surrounded by four Q 3 units or possibly one terminal oxygen instead of a Q 3 unit (60 ppm) and by four Q 4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23 Na MQ NMR in a glass 22.7 Na 2 O 0.7 B 2 O 69.8 SiO 2 .