The structure of phase-separated sodium borosilicate glasses:
a quantitative thermodynamic approach
Natalia M. Vedishcheva1* & Adrian C. Wright2
It is well known that alkali borosilicate glasses can be used for manufacturing porous glasses.
Starting from the mid-1950s, thorough systematic studies at the Institute of Silicate Chemistry
(Leningrad/St. Petersburg) have indicated that high-quality porous glasses can only be
obtained if the phase-separated glasses used for producing porous glasses meet the following
requirements: (i) the phases enriched with SiO2
(spinodal decomposition), (ii) the silica-rich phase contains as much
and (iii) the M2
rich phase readily dissolves in acidic solutions. Here, these
requirements are analysed in terms of the intermediate-range order in the structure of
the initial single-phase glass, (0.08Na2
), as well as in the
chemically unstable phase, 14.8Na2
, and in the high-silica phase,
, into which the initial glass phase separates after heat
treatment at 823K for 140 h. In addition, a model developed on the basis of NMR data,
which shows the connection between the borate and silicate sub-networks in borosilicate
glasses , is used to explain, in structural terms, the origin of secondary dispersed silica
that is present inside the porous space in porous glasses after treatment of the respective
phase-separated glasses with acid.
A.P. Howes et al., Phys. Chem. Chem. Phys., 2011, vol. 13, p. 11919-11928.
1 Institute of Silicate Chemistry of the Russian Academy of Sciences,
Nab. Makarova 2, St. Petersburg, 199034, Russia
2 J.J. Thomson Physical Laboratory, University of Reading,
Whiteknights, Reading, RG6 6AF, U.K.