Heat capacity measurements of 75SiO₂–6B₂O₃–10Al₂O₃–9MO (M=Mg, Ca, Sr and Ba) glasses and melts

Abstract

Heat capacities of 75SiO 2 6B 2 O 3 10Al 2 O 3 9MO (M=Mg,Ca, Sr and Ba) glasses and melts were determined between 345 and 1877 K by differential scanning calorimetry and drop calorimetry. The heat capacities of glasses and melts increase with increasing field strength of alkaline-earth metals. The glass transition takes place when the heat capacity of glass reaches 9597% of Dulong-Petit harmonic limit. The configurational contribution to the melt heat capacity is about 20% and is independent of temperature. The partial molar heat capacity of B 2 O 3 (Cp B2O3 ) in borosilicate melts containing alkaline-earth metals approaches to constant value (110120 J·K ¹1 ·mol ¹1 ) above 1600 K and is consistent with heat capacity of pure B 2 O 3 liquid. This suggests that there are no significant differences in coordination state of boron and in BSi ordering among Mg, Ca, Sr and Ba-bearing alumino-borosilicate melts.

High-temperature heat capacity and density of simulated high-level waste glass

“…Experiments on the a-Al 2 O 3 indicate an internal precision of less than 0.3% for the enthalpies. The inaccuracies between the measured enthalpies for pseudo-wollastonite and those in previous study [17] are less than 0.4% between 1122 K and 1743 K [13]. The heat capacities of sample were determined from the temperature derivatives of the relative enthalpies.…”

“…Heat capacities of the glass melts was determined by drop calorimetry [13]. The drop calorimeter consists of a vertical furnace with LaCr 2 O 4 heating element, a temperature controller and an ice calorimeter [14,15] installed just below the furnace.…”

“…The Cp Conf of aluminosilicate melt increases with increasing temperature (An and Ne in the Fig. 6) and field strength of networkmodifier cations [13,32,33,53]. The positive dCp/dT for the aluminosilicate melts had been considered due to temperature-induced SiAAl disordering in the melts [29,33].…”

“…6b). Partial molar Cp of B 2 O 3 (Cp B2O3 ) varies from 100 to 400 J K À1 mol À1 depending on the temperature and composition [13]. This is in contrast to the alkali titanosilicate melts where the Cp Melt is an additive function of composition [31].…”

“…6b). Furthermore, it is interesting to note that heat capacities of alkali-free alumino-borosilicate melts (E-glass [23], LCD-glass [13]) are independent of the temperature regardless of high concentrations of alkaline-earth oxides. Therefore, it can be expected that interactions between coexisting alkali oxides (Na 2 O, Li 2 O) and alkaline-earth oxides (CaO, MgO) have a key role in the temperature dependence of Si-B network disorder (Eq.…”