Differences in molecular species present in aqueous potassium silicate solutions and their efficiency as adhesives for phosphors on glass

Potassium silicate liquors of very similar composition (SiO₂/K₂O ratios approximately 3.mD4:1) prepared from Aerosil, acid-washed silica-gel fines or potash glass have been examined by (a) light scattering, (b) reaction with molybdate and (c) use of the metachromatic effect with pinacyanol chloride. Definite differences between the molecular weights of the samples were obtained from the light-scattering results. These differences correlated well with the interaction observed between the silicate and pinacyanol chloride and the wet adhesion shown by the silicate; the samples containing more of the very high molecular weight polysilicate showing poor adhesion. The actual molecular weights have been estimated, but the determination of these involved dilutions of the silicate liquors and, over the range of dilution used, the reaction with molybdate showed that rapid depolymerisation of the silicate polyanion occurred on dilution. The results indicate that liquors prepared from potash glass contain more high-molecular-weight material than liquors prepared from silica gel or Aerosil.