, Volume 16, Issue 7, pp 1980-1988

Conversion of monolithic gels to glasses in a multicomponent silicate glass system

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Multicomponent silicate glasses of composition (wt%) 66SiO2-18B2O3-7Al2O3-6Na2O-3BaO were prepared by three sol-gel processes which differed primarily in the extent of hydrolysis of the metal alkoxide precursors. Gels which were prepared from solutions in which a stoichiometric excess of water was added, causing extensive replacement of OR groups (R ≡ (C x H(2x+1))s−1 by hydroxyl groups, were converted to fully dense, organic-free, monolithic glasses at temperatures near the glass transition temperature. Gels containing large numbers of OR groups showed enhanced densification at lower temperatures due to condensation reactions, but these gels could not be converted to fully dense, organic-free glasses. This investigation has shown that at least three possible densification mechanisms might be operative during the gel to glass conversion: volume relaxation, condensation reactions and viscous sintering.

A US Department of Energy Facility.