| When soda-lime-silica glass is heated in contact with zinc chloride
and lead nitrate melts around strain point of the glass, it is observed
that ZnZ+ and PbZ+ ions are introduced in surface layers of
the glass (up to 101-). Average ZnO content up to 41- from the surface
is as high as 5.5 %. Depletion of Ca 2+ ions is also observed. The
phenomenon of bivalent ion exchange in glass is ascribed to the
higher ionic field strengths of ZnZ+ and Pb2+ in comparison to CaZ+,
SEM studies of the thermo-chemically treated samples also reveal
compositional changes in the surface layers whereas X-ray diffraction
patterns do not indicate the presence of any crystalline phase. |
