Enthalpy of mixing of mixed alkali glasses

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

“…This negative enthalpy of mixing was shown to correlate well with the molar volume difference of the corresponding two single alkali glasses with the same total alkali content as well as with the excess activation energy, ΔE, of electric conductivity for a mixed alkali glass system [3]. In the present paper, the effect of alumina addition on the enthalpy of mixing of two alkali silicate glasses was investigated by adding various quantity of Al 2 O 3 to alkali-silicate glasses containing Na 2 O and K 2 O as the alkaline oxide components.…”

“…The enthalpy of mixing, ΔH m , between two alkali-alumino-silicate glasses was determined by establishing ion-exchange equilibria in molten alkali nitrate melts, the same as was done in the previous paper [3] and by Wakabayashi [4]. The glasses employed had compositions of (33 − X)(R 2 O) • XAl 2 O 3 • 67SiO 2 where R 2 O stands for Na 2 O, K 2 O or (0.5Na 2 O• 0.5K 2 O) and X = 5.5, 9.4 and 16.5 mol% .…”

“…It is interesting to note that as the ratio of Al 2 O 3 /R 2 O increased, the molar volume of the single alkali potassium glass remained nearly constant, while the volume of the sodium glass steadily increased. In this paper, unlike the previous paper [3], ΔV, will be defined as the molar volume mismatch as defined below, instead of the absolute difference in molar volume. The volume mismatch is defined as:…”

“…It was previously shown that mixed alkali silicate glasses exhibit a negative enthalpy of mixing by using an ion-exchange method for silicates [3][4][5] and a calorimetric method for a borate system [6]. This negative enthalpy of mixing was shown to correlate well with the molar volume difference of the corresponding two single alkali glasses with the same total alkali content as well as with the excess activation energy, ΔE, of electric conductivity for a mixed alkali glass system [3].…”

“…While many proposed models can explain parts of the mixed alkali effect reasonably well, none can explain all of the anomalous behaviors. This paper seeks to build upon the previously proposed model invoking the thermodynamics of the mixed alkali glasses [3].…”