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

29Si and 23Na 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(Na2Si3O7), where x is varied from x=0 to x=1, (increasing CaO from 0 to 20 mol%) finally matching the Na2O fraction. The glass network becomes increasingly depolymerised by increasing CaO, and shows a changing distribution of Qn 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, Q2, Q3 and Q4 are present. Progressive changes in chemical shifts of Q2 and Q3 species, and changes in FWHM of all detected Qn 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 Q2 species rather than Q3.