HR: 1340h
AN: MR13A-0080    [Abstracts]
TI: The partial molar sound speed of TiO₂ in sodium silicate melts: Evidence for an exceptionally compressible component
AU: * Liu, Q
EM: qiongl@umich.edu
AF: University of Michigan, 2534 C. C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109-1005 United States
AU: Ai, Y
EM: yuhui@umich.edu
AF: University of Michigan, 2534 C. C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109-1005 United States
AU: Lange, R A
EM: becky@umich.edu
AF: University of Michigan, 2534 C. C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109-1005 United States
AB: Longitudinal acoustic velocities were measured at one bar by an ultrasonic frequency sweep acoustic interferometer for ten Na₂O-TiO₂-SiO₂ (NTS) liquids for which previous density and thermal expansion measurements were made (Liu and Lange, 2001). This previous study showed that the partial molar volume of the TiO₂ component varied systematically with composition and reflected changes in the average coordination of Ti⁴⁺ from values of ~4.6 to ~5.4. Sound speed data were collected at frequencies of 4.5, 5, and 6 MHz between 1233 and 1896 K; in all cases, the sound speeds decrease with increasing temperature. Six of the liquids share a similar (~25 mol%) TiO₂ concentration, so that the effect of varying Na:Si ratio on the partial molar sound speed of the TiO₂ component can be evaluated. The results for these ten NTS liquids were combined with sound speed data on Na₂O-SiO₂ liquids from the literature to derive the partial molar sound speed of the TiO₂ component in these liquids. The results show that, at 1573 K, it is inversely correlated with SiO₂ concentration, from values as low as 571±56 m/s to those as high as 1235±54 m/s, a variation of more than 100%. Fitted values for the partial molar sound speeds of the SiO₂ and Na₂O components at 1573 K are constants at 2538±52 and 2713±52 m/s, respectively. When the sound speed data are combined with density data to calculate melt compressibility, the results show that the TiO₂ component is 3-15 more compressible than either the Na₂O or SiO₂ component. The partial molar compressibility of the TiO₂ component is also strongly correlated to its partial molar thermal expansivity. It is shown that the TiO₂ component is most compressible and most expansive when the average Ti⁴⁺ coordination in these sodium silicate liquids is near five, which strongly suggests that the abundance of five-coordinated Ti⁴⁺ enhances topological mechanisms of both compression and thermal expansion.
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3630 Experimental mineralogy and petrology
DE: 8411 Thermodynamics (0766, 1011, 3611)
DE: 8439 Physics and chemistry of magma bodies
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005