Densification kinetics of binary borosilicate glass composite

Densification kinetics and mechanism of a binary borosilicate glass composite, containing low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses, have been studied. Apparent activation energy of densification varies from 200 to 400 kJ/mol, and decreases with increasing BSG content at a given densification factor. At a given BSG content, the activation energy of densification initially remains relatively unchanged with increasing densification factor (DF), but increases with densification when DF reaches a critical value (DF^∗). Moreover, the value of DF^∗ increases with increasing BSG content. From the activation energy estimates of densification, it is concluded that the predominant densification mechanism for BSG ≥ 30 vol. % with DF < DF^∗ is viscous flow of low-softening BSG. For BSG ≥ 30 vol. % with DF < DF^∗ and BSG ⋚ 20 vol. % with all DF investigated, the activation energies are within the range governed by viscous flow of both BSG and HSG, indicating that the densification is controlled by viscous flow of a new glass with a composition between BSG and HSG. The latter evidence stems from the microstructural observation that as sintering proceeds, the HSG particle undergoes an extensive dissolution process.