Criterion for Estimating the Number of Phases in Phase-
separated Glass of the Na₂OK₂OB₂O₃SiO₂ System
by Dilatometric Analysis

S. V. Stolyar, M. Yu. Konon, I. A. Drozdova, and I. N. Anfimova

Grebenshikov Institute of Silicate Chemistry, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034 Russia

e-mail: stolser@yandex.ru

Received October 10, 2013

Abstract—The data of dilatometry and electron microscopy of four series of xNa₂O–(8 – x)K₂O–32B₂O₃–
60SiO₂, xNa₂O–(8 – x)K₂O–22B₂O₃–70SiO₂, xNa₂O–(6 – x)K₂O–34B₂O₃–60SiO₂, and xNa₂O–xK₂O–(40 –
2x)B₂O₃–60SiO₂ phase-separated glass heat-treated at 550C for 144 h (for glass containing 70 mol % SiO₂)
and 24 h (for glass containing 60 mol % SiO₂) for separation on phases are summarized. The comparison of
dilatometric data and electron microscopy allow one to conclude that glass with a difference between the onset
deformation temperature and a glass transition temperature of more than 100C is phase-separated; and glass
with a difference of less than 65C is single-phase. Curves for the glass transition temperature as a function of
the K₂O content reveal a mixed alkali effect, namely, minimums for glass containing 60% SiO₂, and maximums
for glass containing 70% SiO₂.

Keywords: Na₂O–K₂O–B₂O₃–SiO₂ system , phase separation, dilatometry, glass transition temperature, onset
deformation temperature, electron microscopy

DOI: 10.1134/S1087659614030213

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