THERMODYNAMIC PROPERTIES OF THE CeO₂-B₂O₃ SYSTEM

Shugurov S.M.⁽¹⁾, Zhinkina O.A.⁽¹⁾, Lopatin S.I.^(1,2)

⁽¹⁾ St. Petersburg State University

198504, St. Petersburg, p/o Staryi Petergof, Universitetskii av., 26

⁽²⁾ Branch of Petersburg Nuclear Physics Institute named by B.P. Konstantinov
of National Research Centre «Kurchatov Institute» – Institute of Silicate Chemistry

199034, St. Petersburg, Makarova emb., 2

The various CeO₂ based systems is of practical interest because their high ion conductivity and potential using for SOFC. On other hand B2O3 containing system uses as glasses for special purposes. Prediction of the behavior at high temperatures of such systems require the information of quantitative composition of vapor as well as thermodynamic properties (such as activities, activity coefficients and partial thermodynamic functions) for all components. In this study CeO₂-B₂O₃ system was studied by Knudsen effusion mass spectrometry (KEMS) as well as thermodynamics of the gaseous cerium oxyacid salt CeBO₂. Investigation was done using MS 1301 mass spectrometer at the ionization energy equaled to 30 eV. Vaporization of the samples under consideration was carried out from molybdenum and tungsten effusion cells heated by the electron bombardment. Temperature was measured by optical pyrometer EOP-66 with the accuracy ±10. Samples were obtained by heating mixtures of CeO₂ and orthoboric acid.

The B₂O₃⁺, CeO⁺ and CeO₂⁺ ions were detected in mass spectra above the system under study in the temperature range 1500-2100 K. The mass spectrum analyses and appearance energies of ions in mass spectrum shown that the vapor over the systems consist of B₂O₃, CeO, CeO₂ and O molecules. The partial pressures of these vapor species were obtained using the ion current comparison method with silver as inner standard. Additionally gaseous molecule CeBO₂ was detected in the vapor. For this species standard formation enthalpy was derived.

In the studied system ceria is stabilized by second component and decomposition to Ce₂O₃ in the condensed phase wasn't observe. The thermodynamic activities of CeO₂ and B₂O₃ at the temperature 1600 K were found by the differential mass spectrometric method using ceria and B₂O₃ as the standard of the determination of the component activities. The CeO₂-B₂O₃ system demonstrate strong negative deviation from ideal case for boron oxide and weak negative deviation for ceria.