MAS NMR study of soda-lime–silicate glasses with variable degree of polymerisation

29 Si and 23 Na magic angle spinning (MAS) NMR has been used as an atomic probe for structural characterisation of soda-lime–silicate glasses. The glasses studied are based on the composition (CaO) x (Na 2Si 3O 7), where x is varied from x=0 to x=1, (increasing CaO from 0 to 20 mol%) finally matching the Na 2O fraction. The glass network becomes increasingly depolymerised by increasing CaO, and shows a changing distribution of Q n species. Two Q species have been observed co-existing for compositions, where x=0, 0.2 and 1, while for compositions, where x=0.4 and x=0.8, Q 2, Q 3 and Q 4 are present. Progressive changes in chemical shifts of Q 2 and Q 3 species, and changes in FWHM of all detected Q n species accompany the addition of CaO. The addition of CaO introduces a greater distortion into the structure, and there is evidence to suggest preferential arrangement of Ca in the vicinity of Q 2 species rather than Q 3.