PHYSICAL PROPERTIES OF CALCIUM ALUMINATES FROM VIBRATIONAL SPECTROSCOPY

Abstract

Heat capacity (CV) and entropy (S) as a function of temperature were calculated for phases in the CaO-Al2O3 system from vibrational spectra using a quasi-harmonic model. Calculated values of CV at 298 K for the calcium aluminates may have uncertainties as small as ±1%, based on comparison with published calorimetric data for CaO, Al2O3, and CaAl2O4. For hibonite (CaAl12O19), we predict CP as 519.3 J/mol-K and S as 391.7 J/mol-K, at 298 K. For grossite (CaAl4O7), calculated values of CP as 195.9 J/mol-K and of S as 172.0 J/mol-K are slightly smaller than the available calorimetric data at 298 K, consistent with calorimetric data having been obtained from samples containing ∼10 wt% hibonite impurities. 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% and 5%, 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 more accurate than conventional measurements of k0 which are commonly uncertain by ∼25%.