New acoustic velocity measurements on CaO‐MgO‐Al₂O₃‐SiO₂ liquids: Reevaluation of the volume and compressibility of CaMgSi₂O₆‐CaAl₂Si₂O₈ liquids to 25 GPa

Abstract

[1] Relaxed sound speed measurements on 12 liquids in the CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) system have been performed from 1410 to 1620°C at 1 bar with a frequency sweep acoustic interferometer. In all liquids, the sound speeds either decrease or remain constant with increasing temperature. These data are combined with those in the literature to calibrate models for b T and (@V/@P) T as a function of composition and temperature for CMAS liquids. CaO is the only oxide component that contributes to the temperature dependence of compressibility. The new compressibility models permit the bulk modulus (K T,0 ) of CaMgSi 2 O 6 (Di), CaAl 2 Si 2 O 8 (An), and the Di 64 -An 36 eutectic liquid to be directly obtained. These results are used to uniquely constrain values for the pressure dependence of the bulk modulus (K 0 0 = dK 0 /dP) in a third-order Birch-Murnaghan equation of state (EOS) for these three liquids from shock wave data in the literature. The revised K 0 0 value is 6.8 (versus 6.9) for CaMgSi 2 O 6 liquid, 4.7 (versus 5.3) for CaAl 2 Si 2 O 8 liquid, and 5.6 (versus 4.85) for Di 64 -An 36 liquid. Information on both K T,0 and K 0 0 allows the density and compressibility for each of these three liquids to be calculated as a function of pressure to 25 GPa. Both the molar volume and isothermal compressibility of CaMgSi 2 O 6 -CaAl 2 Si 2 O 8 liquids mix ideally between 0 and 25 GPa. The dominant mechanism of compression at low pressure (0-5 GPa) for all three liquids (CaMgSi 2 O 6 , CaAl 2 Si 2 O 8 , and the Di 64 -An 36 eutectic) is topological, whereas gradual Al/Si coordination change plays an increasingly important role at higher pressure as topological mechanisms of compression are diminished.

The K₂CO₃ fusion curve revisited: New experiments at pressures up to 12 GPa

“…However, the error diminishes as the pressure decreases. Figure 3 also illustrates the density versus pressure curves for CaCO 3 liquid (Genge et al, 1995;Vuilleumier et al, 2014), KAlSi 3 O 8 liquid (Lange, 2007), and CaMgSi 2 O 6 liquid (Ai and Lange, 2008). The density of liquid K 2 CO 3 is still significantly lower than those of silicate liquids, which is consistent with that suggested by Liu et al (2007).…”

The compressibility of CaCO3–Li2CO3–Na2CO3–K2CO3 liquids: application to natrocarbonatite and CO2-bearing nephelinite liquids from Oldoinyo Lengai

“…The apparatus was originally designed for application to silicate melts in a reducing atmosphere (e.g., Liu et al 2007a;Ai and Lange 2008), but was adapted in this study for use on CaCO 3 -bearing alkali carbonate liquids in a pure CO 2 atmosphere. The basic design includes both an upper and lower rod in the interferometric circuit, which were originally made of molybdenum metal.…”

Shock compression of preheated silicate liquids: Apparent universality of increasing Grüneisen parameter upon compression

“…The value of γ at ambient conditions is 0.356 [11]. The value at high P was tightly constrained by Asimow and Ahrens [12] from the combination of several pre-heated liquid Hugoniot data and a single high-precision Hugoniot point on an isochemical room-temperature solid aggregate of diopside and anorthite.…”