Compressibility of melts in the CaO-Al2O3-SiO2 system

The effect of composition and temperature on the compressibility of melts in the CaO-Al2O3-SiO2 system has been investigated. The relaxed bulk moduli were measured using ultrasonic interferometric methods at frequencies of 3, 5, and 7 MHz. The measurements were carried out in the temperature range of 1350-1600 degrees C. For these melts, the bulk modulus increases with the addition of CaO and decreases with addition of SiO2 and Al2O3. The bulk moduli of the present alkaline-earth aluminosilicate melts are similar to 50% larger than the adiabatic bulk moduli of the sodium-aluminosilicate melts of Kress et al. (1988). The present data, together with literature data on the bulk moduli of silicate melts show that different structural mechanisms are responsible for the observed compressibility of CaO-Al2O3-SiO2 and Na2O-Al2O3-SiO2 melts.