Quantitative silicon‐29 NMR investigations of highly concentrated high‐ratio sodium silicate solutions

In concentrated alkaline sodium silicate solutions a consistent decrease in the amount of silicate monomer Q 0 , end‐groups Q 1 , cyclic trimer Q groups and middle groups Q 2 , and also branching groups in ring formations Q , is observed with increasing molar ratio of SiO 2 to Na 2 O ( R M), whereas for branching groups Q 3 and cross‐linking groups Q 4 a consistent increase is found. The interest of this work is particularly focused on the Q 4 region, which may indicate the formation of colloidal silicate particles. For this region the 29 Si background signal from the NMR probe and the glass tube can cause problems, so the subtraction technique was used. Spin‐lattice relaxation times, not previously reported for silicate solutions of concentrations and molar ratios as high as those studied here, are given for all structural units, including Q 4 . It was found that sodium silicate solutions of R M = 2.0 do contain a Q 4 region when they are extremely highly concentrated in SiO 2 (38 wt% SiO 2 ) or aged.