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THERMODYNAMIC PROPERTIES OF CaO-Al2O3 MELTS

Shornikov S.I. Center of Isotopic Research, Karpinsky All-Russian Geological Institute (VSEGEI), SaintPetersburg
s_shornikov@hotmail.com Key words: CaO-Al2O3 system, thermodynamic properties of melts, theory of ideal solutions of complex components

Thermodynamic properties of the CaO-Al2O3 are of interest in ceramic and cement technologies, as well as in metallurgy and material science. The high-alumina region of this system is especially interesting for the cosmochemical study of the selective evaporation and condensation of the primitive solar nebula [1]. This work presents the calculation of the thermodynamic properties of the CaO-Al2O3 melts at temperature from 1800 to 2500 K in the framework of the ideal associated solutions theory. The simplified lattice model accounts for the intermolecular interactions using the semi-phenomenological parameters, which were determined on the base of the experimental thermodynamic data [2, 3]. In contrast to the previous calculations made in the frameworks of the sublattice and quasichemical models [4, 5], the initial thermodynamic data considers 12 condensed phases (8 solid and 4 liquid) and 12 gas species; these components are listed in the Table. The same Table gives the calculated values of the Gibbs formation energies for the compounds and the vapor species over the CaO-Al2O3 system, which are used for the calculation of the equilibrium conditions in the system at a given composition and temperature. The equation solution for the integral Gibbs energy for the system studied was found by the widely used approach, namely the Gibbs energy minimization method [6]. The obtained results are shown in Figure and compares with the experimental data obtained by the mass spectrometric Knudsen effusion method in the temperature range 1800-2100 K [7, 8]. As seen from the figure, the deviations in the calculated oxide activities was less than 5 %; resulting in the errors in the Gibbs energies of the melts formation in the CaO-Al2O3 system of 1 kJ/mole with respect to the experimental data heaving the errors of the same order of magnitude. Table The Gibbs energies of formation of condensed phases and vapor species over CaO-Al2O3 melts at 1933 K calculated in the present study on the base of the experimental data [2, 3] Condensed phases fG1933, Liquid phases kJ/mole -1055.518 Al2O3 -428.777 CaO -1545.027 CaAl2O4 -2616.481 -6849.686 -2417.464 -5527.788 -13024.521 Ca12Al14O33 Gas phase Vapor species fG1933, kJ/mole Al 92.545 AlO -70.953 AlO2 -99.424 Al2 199.593 Al2O -279.329 Al2O2 -388.134 Al2O3 -410.309 Ca -15.231 CaO -71.497 O 126.135 O2 0.000 O3 269.935

Solid phases Al2O3 CaO CaAl2O4 CaAl4O7 CaAl12O19 Ca3Al2O6 Ca5Al6O14 Ca12Al14O33

fG1933, kJ/mole -1037.330 -416.203 -1546.931

-13088.549

0.0

a

7

6 5

b
1 2 3 4 7 5 6

0.0

-0.5

-0.5

log a(CaO)

log a(Al2O3 )

-1.0

-1.0

-1.5

-1.5

-2.0

-2.0

-2.5 20 40 60 80 20 40 60 80

-2.5

x(Al2O3 ) , mole %

-10

c
5 6 7 8
20 40 60 80

f GT , kJ/mole

-20

-30

-40

1 2 3 4

x(Al2O3 ) , mole %

Fig. Activities of Al2O3 (a), CaO (b), and the Gibbs energies of formation of the melts of the CaO-Al2O3 system () at 1833 (1, 5), 1933 (2, 6), 2033 (3, 7), and 2060 K (4, 8), obtained by mass spectrometric method (1-3 in [7], 4 in [8]) and calculated in the present study (5-8).

References 1. Yakovlev O.I., Dikov Yu.P., Gerasimov M.V. // Geokhimiya. 2000. 10. P. 1027-1045. 2. Glushko V.P., Gurvich L.V., Bergman G.A., Veitz I.V., Medvedev V.A., Khachkuruzov G.A., Yungman V.S. Thermodynamic Properties of Individual Substances / Ed. V.P. Glushko. M.: Nauka. V. 1-4. 1978-1982. 3. Shornikov S.I., Stolyarova V.L., Shultz M.M. // Russian J. Phys. Chem. 1997. V. 71. 1. P. 23-27 4. Hallstedt B. // J. Amer. Ceram. Soc. 1990. V. 73. 1. P. 15-23. 5. Eriksson G., Pelton A.D. // Metall. Trans. B. 1993. V. 24. 4. P. 807-816. 6. Saxena S.K. // Adv. Phys. Geochem. 1982. V. 2. P. 225-241. 7.Shornikov S.I., Stolyarova V.L., Shultz M.M. // Russian J. Phys. Chem. 1997. V. 71. 1. P. 19-22. 8. Allibert M., Chatillon C., Jacob K.J., Lourtau R. // J. Amer. Ceram. Soc. 1981. V. 64. 5. P. 307314.
Electronic Scientific Information Journal "Herald of the Department of Earth Sciences RAS" 1(21)2003 Informational Bulletin of the Annual Seminar of Experimental Mineralogy, Petrology and Geochemistry 2003 URL: http://www.scgis.ru/russian/cp1251/h_dgggms/1-2003/informbul-1_2003/magm-11e.pdf Published on July 15, 2003 © Department of the Earth Sciences RAS, 1997-2003 All rights reserved