Glass Reflections
Cambridge 7th to 9th September



Presenting Author:
Natalia Vedishcheva
<ionatali386@gmail.com>

article posted 22 Mar 2015

Natalia Vedishcheva

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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 and M2O-B2O3 are interpenetrating (spinodal decomposition), (ii) the silica-rich phase contains as much SiO2 as possible, and (iii) the M2O-B2O3 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, (0.08Na2O 0.22B2O30.70SiO2), as well as in the chemically unstable phase, 14.8Na2O38.3B2O3 46.9SiO2, and in the high-silica phase, 0.19Na2O3.73B2O3 96.07SiO2, 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 [1], 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.

Reference:

A.P. Howes et al., Phys. Chem. Chem. Phys., 2011, vol. 13, p. 11919-11928.

Institutions:

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.