US EPA

608897 

Journal Article 

Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10 

Jacob, K; Shekhar, C; Kale, G 

2009 

Yes 

Journal of Phase Equilibria and Diffusion
ISSN: 1547-7037 

30 

1 

2-11 

10.1007/s11669-008-9423-8 

WOS:000263503100002 

An isothermal section of the system Al2O3-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca3CoAl4O10, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca3CoAl4O10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: $$ ( - ){\text{Pt}},{\text{CaAl}}_{ 2} {\text{O}}_{ 4} + {\text{Ca}}_{ 1 2} {\text{Al}}_{ 1 4} {\text{O}}_{ 3 3} + {\text{Ca}}_{ 3} {\text{CoAl}}_{ 4} {\text{O}}_{ 10} + {\text{Co//(CaO)ZrO}}_{ 2} {\text{//}} {\text{CoO}} + {\text{Co}},{\text{ Pt }}( + ). $$ From the emf of the cell, the standard Gibbs energy change for the Ca3CoAl4O10 formation reaction, CoO + 3/5CaAl2O4 + 1/5Ca12Al14O33 → Ca3CoAl4O10, is obtained as a function of temperature: $$ \Updelta G_{r}^{\text{o}} $$/J mol^{−1} (±50) = −2673 + 0.289 ( T/K). The standard Gibbs energy of formation of Ca3CoAl4O10 from its component binary oxides, Al2O3, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca3CoAl4O10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al2O3-CaO-CoO at 1500 K are presented based on the results... [ABSTRACT FROM AUTHOR] Copyright of Journal of Phase Equilibria & Diffusion is the property of Springer Science & Business Media B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts) 

BINARY systems (Metallurgy); PHASE diagrams, Ternary; SCANNING electron microscopy; ELECTROMOTIVE force; GIBBS' free energy; ISOTHERMAL transformation diagrams; ENTROPY; THERMODYNAMIC potentials; ELECTROMETALLURGY; chemical potential; electromotive force (emf); enthalpy of formation; experimental thermodynamics; Gibbs energy; ternary phase diagram