A Criterion for Evaluating the Thermal Stability of Glasses

Abstract

To evaluate the stability of glasses, a new criterion k f (T) ) ν exp[-E/RT‚(T p -T f )/T f ] is proposed, where T f is the inflection point temperature and T p is the maximum peak temperature on the differential thermal analysis curves. Not only the kinetic parameters of the crystallization of glasses, namely, activation energy, E, and frequency factor, ν, but also a thermodynamic factor (T p -T f )/T f have been taken into account in the k f (T) criterion. A higher value of k f (T) means a poor stability of glasses. Two glasses with the compositions of Li 2 O‚2SiO 2 and Li 2 O‚1.5SiO 2 were prepared by the conventional melting process and the validity of the proposed criterion is ascertained by applying it on these glasses. The stability of these two glasses was also evaluated by the existing criteria. The results indicate that all existing criteria are either affected by the heating rate or they are not suitable for evaluating the stability of these glasses. On the contrary, the new criterion is independent of the heating rate and gives consistent results on the evaluation of the stability of Li 2 O-SiO 2 glasses within a large temperature range. The Li 2 O‚1.5SiO 2 glass is less stable than the Li 2 O‚2SiO 2 glass.

Chemical compatibility between MgO–SiO2–B2O3–La2O3 glass sealant and low, high temperature electrolytes for solid oxide fuel cell applications

“…Frequency factors are listed in Table 3 and the value of frequency is obtained from the intercept of equation (3) by the least-squares fitting method [41,29]. Low n value and high E c for ML imply smaller crystallization tendency in these glasses which is in good agreement with X-ray diffraction pattern (discussed later).…”

“…Maximum value of n will indicate instability of glass. Apart from this, the rate of crystallization k has been evaluated using following relations [40,41]. …”

“…Minimum values of k indicate decrease in crystallization and hence increase in glass forming ability. The new k criterion as suggested by Cheng [41] takes (T c À T f ) into account, where T f is the inflection point temperature. DTA curves were differentiated and hence derivative differential thermal analysis (DDTA) was obtained.…”

Internal friction spectroscopy in Li2O–2SiO2 partially crystallised glasses

“…effect of variations in cooling rate is approximately þ13.5°C/logðK min À1 Þ obtained from DSC [17] and approximately þ35.6°C/logðK min À1 Þ obtained from DTA [16]. These variations in T g imply a significant increase in the shear viscosity with an increasing cooling rate from þ0:8 to þ1:93 logðPa sÞ= logðK min À1 Þ, respectively.…”

“…1). This cooling rate infers a T g of the glass matrix of %440°C according to DTA measurements [16]. DSC series on lithium disilicate glasses prepared at cooling rates between 0.3 and 2 K/min indicate T g % 445°C [17].…”