St. Catharines 2004
Technical Program


SS19:  Molecules to Planets: Infrared spectroscopy in geochemistry, exploration geochemistry and remote sensing 
Organizers / Organisateurs:  Penny King, Mike Ramsay, Gregg Swayze
Room / Salle:  AS 201

Date:  05/12/2004
Time:  8:00 AM
Presenter:  Anne M. Hofmeister


Physical properties of calcium aluminates from vibrational spectroscopy

Hofmeister, A.M. Department of Earth and Planetary Sciences, Washington University, St. Louis, MO, USA, 63130, hofmeist@levee.wustl.edu

Heat capacity (CV) and entropy (S) as a function of temperature were calculated from IR and Raman vibrational spectra for phases in the CaO-Al2O3 system using a quasi-harmonic model.  The calculated values of CV for the calcium aluminates at 298°K are more accurate that digital scanning calorimetry (3 percent), and may have uncertainties as small as 1 percent, based on the comparison of our calculations to published calorimetric data on CaO, Al2O3, and CaAl2O4. For hibonite (CaAl12O19), we predict CP as 519.3 J/mol-K and S as 391.7 J/mol-K, both at 298°K. For grossite (CaAl4O7), our calculated values of CP as 195.9 J/mol-K and of S as 172.0 J/mol-K (both at 298°K) are slightly smaller than the available calorimetric data, which is consistent with acquisition of thermodynamic data from samples containing small amounts of hibonite intergrown with grossite. Thermal conductivity at 298°K (k0) is predicted from peak widths of the vibrational modes using the damped harmonic oscillator model of a phonon gas. Calculations of k0 for CaO and Al2O3 differ from the measurements by 17 percent and 5 percent, respectively. The discrepancy for lime is larger due to uncertainties in its peak widths. This comparison suggests that our results for the calcium aluminates should be as least as accurate as conventional measurements, which provide k0 within ~25 percent.