Temperature Dependence of the Density of Stabilized Sodium Borate Glass at Temperatures Below the Glass Transition Tempe
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mperature Dependence of the Density of Stabilized Sodium Borate Glass at Temperatures Below the Glass Transition Temperature N. S. Yuritsyn* Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, 199034 Russia *e-mail: [email protected] Received December 26, 2019; revised March 16, 2020; accepted April 3, 2020
Abstract—The density of glass with a composition of 20Na2O ∙ 80B2O3 (mol %) (glass transition temperature Tg = 450°С) during stabilization in the temperature range 390−424°С and the temperature dependence of the density of the stabilized glass in the range 390–469°С are studied. We aim to study the temperature dependence of the density of stabilized glass ds lower than the glass transition temperature. The density is determined after quenching the samples at room temperature by hydrostatic weighing in kerosene with an accuracy of ±0.0005 g/cm3. It is found that, in the temperature range 450−420°C, density ds increases linearly with decreasing temperature. In the range 420−402°C, there is a deviation from the linear dependence ds(T) towards lower density values. At 390°C, after reaching the stabilized state of the glass, the density obtained is the same as at 402°C. For this glass, the existence of temperature Ts = 402°C (48°C less than Tg) is established, below which the structure of stabilized glass ceases to change. Keywords: sodium borate glass, glass stabilization, density DOI: 10.1134/S1087659620040148
INTRODUCTION Studies of the properties of stabilized glass at temperatures below the glass transition temperature Tg are important for understanding the nature of the glassy state. Stabilized glass below Tg can be considered as a highly viscous metastable liquid. The temperature dependence of the property of stabilized glass is a natural extension of the temperature dependence of this property of a metastable liquid at temperatures above Tg. The time to establish a stabilized glass structure increases rapidly with decreasing temperature as a result of an increase in viscosity. It is possible to trace the change in the properties of stabilized glass with decreasing temperature only a few tens of degrees below Tg. The temperature dependence of the density of stabilized glass in earlier studies showed that it increases approximately linearly with decreasing temperature [1–3]. The linear change in temperature with the other properties of stabilized glass led to attempts to extrapolate them to low temperatures. The Kauzmann paradox [4–6] is discussed in the literature, which manifests itself in the intersection of the temperature dependence of the entropy of a metastable liquid during its linear extrapolation to low temperatures with the temperature dependence of the crystal entropy. The solution to the paradox may lie in the assumption that as the temperature decreases the temperature dependence of the entropy of the metastable liquid gradually deviates from linear to the side, pre-
venting it from intersecting with the temperature dependence of the crystal entropy. Simi
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