Shrinkage behavior of Knoop indentations in silica and soda-lime-silica glasses

The annealing characteristics of Knoop-indented silica and soda-lime-silica glasses were investigated. These glasses were indented using a Knoop inden ter in water, and they were annealed at various temperatures below the glas s transition temperature. The major diagonal length of the Knoop indentatio n was measured before and after annealing, and the change of the diagonal l ength was determined. The change of diagonal length in silica glass was muc h larger than that in soda-lime-silica glass. This was attributed to the oc currence of more densification around the Knoop indentation in the silica g lass. The activation energy of the shrinkage of the Knoop indentation in th e silica glass, estimated from the temperature dependence of the relaxation time, was 46 kJ/mol, which was: much less than that of viscous flow in sil ica glass. This: suggested that the shrinkage of the Knoop indentation was caused by the structural relaxation of densified glass around the Knoop ind entation.